Download Extreme Storms in Michigan

EXTREME STORMS
IN MICHIGAN
Principal Authors
Stephen Saunders and Tom Easley
The Rocky Mountain Climate Organization
Contributing Authors
Melissa Mezger and Dan Findlay
The Rocky Mountain Climate Organization
Theo Spencer
Natural Resources Defense Council
December 2014
About RMCO
About the Authors
The Rocky Mountain Climate Organization (RMCO)
works to reduce climate disruption and its impacts.
We do this in part by spreading the word about what
a disrupted climate can do to us and what we can do
about it. Visit www.rockymountainclimate.org to learn
more about our work.
Stephen Saunders is the president, Tom Easley is the
director of programs, and Melissa Mezger and Dan
Findlay are senior fellows at RMCO. Theo Spencer is a
senior advocate in NRDC’s Climate Center.
About NRDC
Acknowledgements
The Natural Resources Defense Council (NRDC) is an
international nonprofit environmental organization
with more than 1.3 million members and online
activists. Since 1970, our lawyers, scientists, and
other environmental specialists have worked to
protect the world’s natural resources, public health,
and the environment. NRDC has offices in New York
City; Washington, DC; Los Angeles; San Francisco;
Chicago; Bozeman, Montana; and Beijing. Visit us at
www.nrdc.org.
The authors express their appreciation to the
following people for reviewing drafts of this report
or providing information or other assistance: Haris
Alibašić, Office of Energy and Sustainability, City of
Grand Rapids; Daniel Brown, Graham Sustainability
Institute, University of Michigan; Lorraine Cameron,
Division of Environmental Health, Michigan
Department of Community Health; Steve Hamilton,
Department of Zoology and Kellogg Biological Station,
Michigan State University; Stephen Handler, Northern
Institute of Applied Climate Science, U.S. Forest
Service; Charles Hill, Water Resources Division,
Michigan Department of Environmental Quality;
Christopher Hoving, Wildlife Division, Michigan
Department of Natural Resources; Kenneth Hozak,
Water Resources Division, Michigan Department of
Environmental Quality; Michael Notaro, Center for
Climatic Research, Nelson Institute for Environmental
Studies, University of Wisconsin-Madison; and Donald
Scavia, Graham Sustainability Institute, University of
Michigan.
The cover photo, of Grand River floodwaters outside
an office building in Grand Rapids in April 2013, is
copyright by Cory Morse, MLive.com, and reproduced
by permission; all rights are reserved. The map in
Figure 4 on page 5 was prepared by Juan DecletBarreto, NRDC, using a base map by Esri.
The Rocky Mountain Climate Organization
P.O. Box 270444, Louisville, CO 80027
303-861-6481
www.rockymountainclimate.org
Natural Resources Defense Council
40 West 20th Street, New York, NY 10011
212-727-2700 / Fax 212-727-1773
www.nrdc.org
© 2014 by the Rocky Mountain Climate Organization and
the Natural Resources Defense Council.
Table of Contents
Executive Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
Section 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Section 2. More Extreme Storms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Storms by Size
Total Precipitation
Extreme Storms: Regional Trends
Extreme Storms: Seasonal Trends
Consistency with Previous Studies
Section 3. Floods and Other Impacts . . . . . . . . . . . . . . . . . . . . . . . . . Floods
Effects on Public Health
Other Impacts
9
Section 4. More Pollution, More Storms . . . . . . . . . . . . . . . . . . . . . . . 16
Section 5. Actions to Address Extreme Storms . . . . . . . . . . . . . . . . . . 19
Appendix: Research Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Attribution to Human-Caused Climate Change
Future Extreme Storms
Climate Preparedness
Emission Reductions
Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
i
List of Tables
List of Figures
Table ES-1. Michigan Precipitation Changes by
Storm Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
Figure ES-1. Michigan Frequency of 2-InchesPlus Storms, 1964–2013 . . . . . . . . . . . . . . . . . . iv
Table 1. Michigan Precipitation Changes by Storm
Size. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Figure ES-2. Projected Changes in Decadal
Frequency of Michigan 2-Inches-Plus Storms . . . . vi
Table 2. Regional Frequencies by Storm Size . . . . . 6
Figure 1. Michigan Frequency of 2-Inches-Plus
Storms, 1964–2013 . . . . . . . . . . . . . . . . . . . . . 3
Table 3. Seasonal Frequencies of 2-Inches-Plus
Storms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Figure 2. Michigan Frequency of 1–2 Inches
Storms, 1964–2013 . . . . . . . . . . . . . . . . . . . . . 4
Table 4. Locally Largest Combined Sewer
Overflows in Michigan. . . . . . . . . . . . . . . . . . . . . 13
Figure 3. Michigan Frequency of Under 1–Inch
Storms, 1964–2013 . . . . . . . . . . . . . . . . . . . . . 4
Table App-1. Analyzed Weather Stations . . . . . . . 22
Figure 4. Weather Stations and Regions for
Regional Analysis . . . . . . . . . . . . . . . . . . . . . . . 5
Figure 5. Southern Michigan Frequency of
2-Inches-Plus Storms, 1964–2013 . . . . . . . . . . . 7
Figure 6. Total Precipitation, June 1–15, 2008 . . . . 10
Figure 7. Projected Changes in Decadal
Frequency of Michigan 2-Inches-Plus Storms . . . . 18
ii
EXECUTIVE SUMMARY
T
This report presents new evidence that in Michigan large storms have become much more frequent over
the past half century. This information comes from a new analysis done for this report of daily precipitation
records from 37 weather stations in Michigan. Those stations were selected for having complete or nearly
complete records for the period of analysis and for having a geographic distribution that makes them
representative of the state and the regions within it. This analysis is unique in its focus on Michigan, its
inclusion of enough geographically distributed weather stations to support not only statewide but sub-state
conclusions, and its inclusion of data through the end of 2013.
MORE EXTREME STORMS
This new analysis shows that the annual frequency of Michigan storms of two inches or more of precipitation in
a single day has increased by 89% between 1964 and 2013. This is a far larger change than is true for smaller
storms, as shown in Table ES-1.
Michigan Precipitation Changes by Storm Size
Trends in Annual Values, 1964–2013
2-Inches-Plus Storms
1–2 Inches Storms
Under-1-Inch Storms
Table ES-1. Trends over 50 years (1964-2013) in the annual frequencies of Michigan storms by size:
those with two inches or more of precipitation in a day, at least one inch but less than two inches, and less
than one inch. These trends are all statistically significant with a 95 percent confidence level.
The largest storms, those with two inches or more of precipitation in a day—called extreme storms in
this report—are rare. Over the 50 years of this analysis, a location in Michigan averaged two of these large
storms every three years. While rare, these extreme storms can be highly destructive, which makes the large
increase in their frequency of great significance in Michigan.
Figure ES-1 on the next page shows Michigan’s annual rates of extreme storms for 1964 through 2013
(the circles), as well as the linear trend—the straight line that is the best statistical fit with those annual
frequencies.
iii
Michigan Frequency of 2-Inches-Plus Storms, 1964–2013
Trend 1964 to 2013:
89% increase over 50 years
1.0
2010
2005
2000
1995
1990
1985
1980
1975
1970
0.5
1965
Storms per station per year
1.5
Figure ES-1. Average frequency of days with 2 inches or more of precipitation per station per year. Dots indicate annual values of
average frequency per station, and the dark red line the 1964-2013 linear trend line.
The analysis done for this report also considered changes in precipitation patterns in different parts of
Michigan:
• the Upper Peninsula;
• the northern Lower Peninsula–north of latitude 44° north, or essentially north of the tip of the Thumb; and
• southern Michigan–the southern half of the Lower Peninsula, south of latitude 44° north.
From 1964 through 2013, the annual frequency of extreme storms in southern Michigan more than doubled,
with a 128% increase over 50 years—nearly half again as large as the 89% increase for the entire state, and
much higher than the rates of increase in the other parts of the state. The sharp increase in the frequency of
extreme storms in southern Michigan is especially important because this is where most people in the state
live.
FLOODS, HEALTH EFFECTS, AND OTHER IMPACTS
Extreme storms matter in Michigan because of their impacts—most importantly, destructive flooding. Floods
are to Michigan and other states in the Midwest what hurricanes are to the Atlantic coast areas—the most
destructive type of regularly occurring natural disaster in the region. Across the United States, flooding
is the second most costly type of natural disaster, ranking behind only hurricanes and ahead of drought,
earthquakes, coastal disasters (including storm surges, coastal flooding, and erosion), tornadoes, and other
types of natural disasters.
Michigan’s vulnerability to flooding caused by extreme storms is illustrated by 2013. In that year, which
had the fourth most two-inches-plus storms in Michigan in the past half century, extreme storms in April
iv
2013 caused flooding so extensive that it led to a federal disaster designation covering 16 counties in the
state. In 2008, the year out of the past 50 years with the most extreme storms, those storms led to flooding
destructive enough to have 11 Michigan counties designated by the federal government as a major disaster
area.
A particular vulnerability that Michigan has to extreme storms stems from the state’s reliance on combined
sewer systems, an older type of system which carries both storm water and sewage in the same pipes.
Michigan has 46 combined sewer systems, the third-largest total in the nation. Combined sewer systems are
designed to overflow when stormwater exceed their capacities, discharging untreated sewage and stormwater
directly to nearby water bodies. These combined sewer overflows (CSOs) can spread untreated human and
industrial wastes, and people can become sick by drinking or being exposed to the contaminated water.
For this report, a new analysis was made of how many of a representative sample of recent overflows
from combined sewers in Michigan were linked to this report’s definition of an extreme storm—one with two
inches or more of precipitation in a single day. Of the largest recent CSOs from each of 17 combined sewer
systems in Michigan having overflows, 13 were associated with two inches or more of precipitation in a day.
This illustrates the importance of extreme storms in driving CSOs and threatening the health of the people of
Michigan.
MORE POLLUTION, MORE STORMS
The increase in extreme storms documented in this report is part of a global increase in heavy precipitation
that scientists say stems from human disruption of the natural climate. Under the laws of physics, warmer air
holds more moisture than cooler air does, increasing the likelihood for extreme precipitation when a storm
does occur in a hotter climate. Scientists have documented, across the nation and the planet, larger change in
extreme precipitation than in median precipitation. That this expected change is already underway has added
to the confidence of scientists that human influences are already changing Earth’s climate.
Scientists also project that if emissions of heat-trapping pollution continue to grow, further increases in large
storms will result, especially in the Midwest. Climate projections commissioned by the Michigan Department
of Natural Resources and others include that with low future emissions of heat-trapping pollution, by midcentury the frequency of Michigan two-inches-plus storms could be one or two storms per decade higher
than in 1961-2000, and by late in the century about two or three storms per decade higher, with variations in
different parts of the state. With medium-high future emissions, by mid-century the increases could instead
be about one to three storms per decade and by late in the century about three to six storms per decade.
The important point from these projections, shown in Figure ES-2 on the next page, is that the frequency of
extreme storms in Michigan is expected to increase more if future emissions in heat-trapping pollution are
higher, and less if future emissions are lower.
v
Projected Changes in Decadal Frequency of Michigan 2-Inches-Plus Storms
A. 2046-2065
Low Emissions
B. 2046-2065
Medium-High
Emissions
D. 2081-2100
Medium-High
Emissions
C. 2081-2100
Low Emissions
Change
in number
per
decade
7
3
6
2
5
1
4
0
Figure ES-2. Projected changes in the frequency of Michigan two-inches-plus storms, in the average number of storms per
decade compared to 1961-2000. Averages of downscaled results from nine global climate models each for low and for mediumhigh future emissions.
vi
ACTIONS TO ADDRESS EXTREME STORMS
To address the increase in extreme storms and floods, Michigan can both prepare for those events and limit
its emissions to do its part to reduce the future severity of those events. Actions by both the state and local
governments can play a role in limiting the worst effects of climate change and the extreme storms it fuels,
and will be most effective if undertaken with a framework of national (and global) actions and in concert with
actions by the private sector.
Some specific steps have been taken by the state government and by some local governments in Michigan
to prepare for a further increase in extreme storms and their impacts, but more actions are needed. An
important first step in preparing for climate change impacts is assessing local vulnerabilities. Many states have
prepared statewide vulnerability assessments, but no comprehensive statewide assessment of climate change
impacts has yet been prepared specifically focused on Michigan’s vulnerabilities.
Holding down future emissions of heat-trapping pollution would lead to smaller future increases in the
frequency of extreme storms, so emission reduction actions ultimately are important to address extreme
storms. Again, some specific steps have been taken by the state government, by some local governments
in Michigan, and by others, but more actions are needed for Michigan to do its part to reduce emissions
enough to help avoid unacceptable impacts from extreme storms and other events being fueled by a disrupted
climate.
vii
1. INTRODUCTION
A
An August 2014 storm deluged Detroit with up to six
Extreme weather has become more
inches of rainfall in eight hours, flooding the metro
common in recent decades. This report
area, causing about $1.1 billion in damages, and
leading to a federal disaster designation.1 In April
documents the change in extreme weather
2013, widespread storms dropped more than two
most important to the Midwest: an increase
inches of rainfall in a day, flooding sixteen Michigan
in the frequency of heavy storms.
2
counties, and also prompting a disaster designation.
These events are part of a pattern documented
in this report, which presents new evidence that
in Michigan large storms have become much more frequent over the past half century. For Michigan, the
increasing number of extreme storms is one of the state’s greatest vulnerabilities to human-caused climate
change.
The increase in the number of extreme storms in Michigan is part of a pattern of more extreme weather,
across the globe and in the United States. Increasingly, scientists are concluding that many types of extreme
weather are being driven by human alteration of the climate.3 In Michigan, the most significant form of
extreme weather is heavy precipitation, as it is the primary cause of major floods, which in the United States
are second only to heat waves as the most deadly type of extreme weather and second only to hurricanes as
the most costly type of natural disaster.4
Section 2 of this report documents the changing pattern over the past half century of precipitation in
Michigan, presenting the results of a new analysis showing that extreme storms in the state have become
much more frequent since 1964, while the frequencies of smaller storms have changed much less. The
greatest increase in extreme storms has been in southern Michigan, where most Michiganders live.
Section 3 links extreme storms to Michigan floods, showing why it matters so much that extreme storms
there are becoming more frequent. The section also includes a new analysis linking extreme storms to
combined sewer overflows, showing how an increase in extreme storms is a public health risk.
Section 4 documents that the large increases in extreme storms detailed here are consistent with worldwide
and regional increases in extreme precipitation that have been attributed to human-caused climate change.
The section also documents that extreme storms are projected to continue becoming more frequent, with
future changes depending on emission levels of heat-trapping pollution.
Section 5 identifies actions that can be taken in Michigan to address the increase in extreme storms.
An Appendix details the sources and methodologies for the new analysis reported here.
“Observations show that heavy downpours have already increased
nationally. . . . For the heaviest, most rare events, there is strong
evidence from observations and models that higher temperatures
and the resulting moister atmosphere are the main cause of these
observed and projected increases.”
U.S. Global Change Research Program5
1
2. MORE EXTREME STORMS
B
Big storms can mean big floods, and the largest of
Statewide across Michigan, the annual
storms are coming much more often in Michigan.
frequency of extreme storms has increased
The annual frequency of storms of two inches or
more of precipitation in a single day has increased by
by 89 percent over the past 50 years. In
89% between 1964 and 2013. In southern Michigan,
southern Michigan, the increase has been
where most of the state’s people live, the change has
128 percent.
been much greater—a 128% increase over those 50
years. We consider these to be the most important
changes in Michigan’s precipitation patterns over the
last half century.
This information comes from a new analysis done for this report of daily precipitation records from 37
weather stations in Michigan. Those stations were selected for having complete or nearly complete records for
the period of analysis and for having a geographic distribution that makes them representative of the state
and the regions within it. (See the Appendix for details on the weather stations and the methodology used in
the analysis.) This analysis is unique in its focus on Michigan, its inclusion of enough geographically distributed
weather stations to support not only statewide but sub-state conclusions, and its inclusion of data through the
end of 2013.
STORMS BY SIZE
The most significant change in statewide Michigan precipitation trends is revealed by an analysis of changes in
storms by size. Large storms have become more frequent by a far greater rate than is true for smaller storms.
Table 1 shows the changes over 50 years in the annual frequencies of Michigan storms of different sizes: those
with less than one inch of precipitation in a single day, those with at least one and less than two inches, and
those with two inches or more. All such trends identified in this report are the change over 50 years, from
the start (in 1964) to the end (in 2013) of a linear trendline representing the best statistical fit with the data
(as illustrated in figures 1, 2, and 3.) Unless indicated otherwise, all such trends identified in this report are
statistically significant with a 95 percent confidence level.
Michigan Precipitation Changes by Storm Size
Trends in Annual Values, 1964–2013
Frequency
Of Storms
Precipitation
Per Day
Annual
Precipitation
Amount
2-Inches-Plus Storms
+ 89%
+ 4%
+ 94%
1–2 Inches Storms
+ 24%
no change
+ 25%
Under-1-Inch Storms
+ 12%
- 6%
+5%
Storms by Size
Table 1. Trends over 50 years (1964-2013) in the annual frequencies of Michigan storms by size:
those with two inches or more of precipitation in a day, at least one inch but less than two inches, and
less than one inch. See the Appendix for details on sources and methodology.
2
The largest of storms, those with two inches or more of precipitation in a day—called extreme storms in this
report—are rare. Over the 50 years of this analysis, a typical location in Michigan averaged two of these large
storms every three years. While rare, these extreme storms can be highly destructive, which makes the large
increase in their frequency of great significance in Michigan. (See Section 3 of this report for details of the
impacts of these storms.)
Figure 1 below shows Michigan’s annual rates of extreme storms for 1964 through 2013 (the circles),
as well as the linear trendline, as described above. That line in the figure displays the same 89% increase
over 50 years shown above in Table 1. The rate of change was not uniform over this period; of the five nonoverlapping 10-year periods within these 50 years, the largest change was in 1974-1983, which had a 67%
increase over 10 years, and the second largest change was in 2004-2013, which had a 22% increase.
Michigan Frequency of 2-Inches-Plus Storms, 1964–2013
Trend 1964 to 2013:
89% increase over 50 years
1.0
2010
2005
2000
1995
1990
1985
1980
1975
1970
0.5
1965
Storms per station per year
1.5
Figure 1. Average frequency of days with 2 inches or more of precipitation per station per year. Dots indicate annual values of
average frequency per station, and the dark red line the 1964-2013 linear trend line. See the Appendix for details of sources
and methodology.
Of the 10 years with the most two-inches-plus storms, five have been in the first 14 years of the 21st
century, including three of the top four: 2008 (the top year), 2010 (third highest), and 2013 (fourth). Of
these, 2008’s number of extreme storms was far ahead of all other years, with 26% more than 1986 (the
second-place year).
Section 3 presents accounts of the flooding that occurred in the years with the most extreme storms—
especially in 2013, 2008, and 1986, years which had not only many extreme storms but also some of the
worst floods in Michigan’s history. The information in that section makes it clear that the increasing frequency
of extreme storms is of great consequence to the people of Michigan.
Figures 2 and 3 on the next page show the annual rates and trends for storms of at least one inch but less
than two inches of precipitation in a day, and for storms of less than one inch. Figures 1, 2, and 3 are all
3
sized so that the steepness of the trend lines is shown according to a consistent scale. A trend line showing,
for example, a 50% increase over 50 years would be as steep in any one figure as in the others. As a result,
these figures, taken together, visually illustrate how extreme storms have increased in Michigan much more
than have smaller storms.
Michigan Frequency of 1–2 Inches Storms, 1964–2013
6
4
2010
2005
2000
1995
1990
1985
1980
1975
1970
2
1965
Storms per station per year
Trend 1964 to 2013:
24% increase over 50 years
Figure 2. As Figure 1, but with respect to storms of at least one inch and less than two inches of precipitation in a day.
Michigan Frequency of Under-1-Inch Storms, 1964–2013
150
100
2010
2005
2000
1995
1990
1985
1980
1975
1970
50
1965
Storms per station per year
Trend 1964 to 2013:
12% increase over 50 years
Figure 3. As Figure 1, but with respect to storms of less than one inch in a day.
TOTAL PRECIPITATION
The total amount of annual precipitation (from storms of all sizes) in Michigan has increased at a rate of 12%
over 50 years (the analyzed period of 1964-2013). This increase was driven by a similar change in the annual
number of days with precipitation, which increased by a 13% rate over those 50 years. The average amount
of precipitation in an individual wet day did not change significantly over the 50-year period. Similarly, the size
of extreme storms in Michigan did not become significantly larger, when measured in terms of the amount of
4
precipitation per event for a storm with two inches or more of precipitation in a day. Over the 50 year period
analyzed here, the average size of these storms increased by only 4%. However, storms lasting for hours
but not a full day (which can sometimes cause flash floods) or for two or more consecutive days could have
different trends than those reported here.
EXTREME STORMS: REGIONAL TRENDS
The analysis done for this report also considered changes in precipitation patterns in different parts of
Michigan:
• the Upper Peninsula;
• the northern Lower Peninsula–north of latitude 44° north, or essentially north of the tip of the Thumb; and
• southern Michigan–the southern half of the Lower Peninsula, south of latitude 44° north.
Figure 4 below shows the demarcation between the northern Lower Peninsula and southern Michigan for this
analysis and the location of the weather stations used in this analysis. (For the identification of the stations,
see the Appendix.) The regional analysis is based on 10 stations in the Upper Peninsula, nine in the northern
Lower Peninsula, and 18 in southern Michigan.
Weather Stations and Regions for Regional Analysis
Figure 4. Location of weather stations analyzed for this report, and the diving line (latitude 44°
north) between the northern Lower Peninsula and Southern Michigan as those regions are
defined for the regional analysis in this report.
5
Table 2 below shows that over the 50-year period analyzed for this report, the annual frequency of extreme
storms in southern Michigan more than doubled, with a 128% increase over 50 years— nearly half again as
large as the 89% increase for the entire state, and much higher than the rates of increase in the other parts of
the state. The sharp increase in the frequency of extreme storms in southern Michigan is especially important
because this is where most people in the state live.
Regional Frequencies by Storm Sizes
Trends in Annual Rates, 1964–2013
Upper Peninsula
2-Inches-Plus Storms
+ 62%
1–2 Inches Storms
+ 6%
Under-1-Inch Storms
+ 9%
Northern Lower Peninsula
2-Inches-Plus Storms
+ 42%
1–2 Inches Storms
+ 25%
Under-1-Inch Storms
+ 21%
Southern Michigan
2-Inches-Plus Storms
+ 128%
1–2 Inches Storms
+ 29%
Under-1-Inch Storms
+ 9%
Table 2. Trends over 50 years (1964-2013) in the annual frequencies of storms of
different sizes (as in Table 1 on page 2) for regions in Michigan (see the text for
descriptions). Trends are statistically significant except for all trends in the Upper
Peninsula, for 2-inches-plus storms in the northern Lower Peninsula, and for 1-2
inches storms in southern Michigan. See the Appendix for details of sources and
methodology.
Figure 5 on the next page shows the frequency of two-inches-plus storms in southern Michigan and the
trend line over the period 1964-2013. This figure is similar to Figure 1 (on page 3), except with respect to the
region rather than to the entire state, and is scaled the same as that figure for accurate comparison between
them. As with the statewide change, the increase was not steady throughout the period, with the largest
change over the last ten years (2004-2013), which had a 58% increase over those 10 years, and the second
largest change in 1974-1983, which had a 48% increase.
6
Southern Michigan Frequency of 2-Inches-Plus Storms, 1964–2013
2.5
Trend 1964 to 2013:
128% increase over 50 years
Storms per station per year
2.0
1.5
1.0
2010
2005
2000
1995
1990
1985
1980
1975
1970
1965
0.5
Figure 5. As Figure 1 on page 3, except with respect only to southern Michigan, defined here as the Lower Peninsula south of
latitude 44 north. See the Appendix for details of sources and methodology.
Over the past 50 years, the ten with the most extreme storms in southern Michigan include five in the 21st
century: 2008 (the top year), 2000 (third most), 2013 (fifth), 2011 (sixth), and 2009 (ninth).
7
EXTREME STORMS: SEASONAL TRENDS
The analysis for this report also considered changes in the seasonal frequencies of Michigan’s two-inchesplus storms. Table 3 below shows that the frequency of extreme storms has increased in all seasons, with the
largest increase—and the only one that is statistically significant—in spring. (A general rule of thumb is that it
takes about 10 inches of snow to equal one inch of water, so a two-inches-plus storm made up of snow would
be a snowfall of about 20 inches or more.)
Seasonal Frequencies of 2-Inches-Plus Storms
Trends in Annual Rates, 1964–2013
Winter
+130%
Spring
+ 335%
Summer
+ 44%
Fall
+ 114%
Table 3. Trends over 50 years in the seasonal frequencies of 2-inches-plus
Michigan storms from 1964 through 2013. Seasons are December-February
(winter), March-May, June-August, and September-November. Only the
spring trend is statistically significant. See the Appendix for details of
sources and methodology.
The large percentage increase in spring extreme storms shown in Table 3 is consistent with projections by
scientists that in the Upper Midwest human-caused climate change will particularly increase spring and early
summer extreme precipitation. This may be considered one piece of evidence, along with others (see Section
4), that the increase in Michigan’s extreme storms is being fueled by human-caused climate change.
CONSISTENCY WITH PREVIOUS STUDIES
Many previously published scientific studies have found for the planet as a whole, the conterminous United
States, and for the Midwest the same trends this new analysis shows for Michigan—that extreme precipitation
has increased at a higher rate than has total precipitation. As a 2008 U.S. government interagency scientific
report on climate and weather extremes summarized, “All studies indicate that changes in heavy precipitation
frequencies are always higher than changes in precipitation totals.”6
In a 2012 report, the Rocky Mountain Climate Organization (RMCO) and the Natural Resources Defense
Council (NRDC) documented that across the eight midwestern states the frequency of three-inches-plus
storms more than doubled between 1961 and 2011.7 That report was similar in many respects to this one, but
focused on three-inches-plus storms, which represent the top 0.3% of all wet days across the full Midwest—
about the same percentage as two-inches-plus storms in Michigan, which represent the top 0.4% of wet days
in that state. Three-inches-plus storms in Michigan, by contrast, represent only 0.08% of wet days, too few for
reliable analysis of trends. This report also is based on an analysis of 37 Michigan weather stations, compared
to 23 in the RMCO-NRDC Midwest report (out of a total of 227 across the region).
For Wisconsin, the Wisconsin Initiative on Climate Change Impacts reported that the frequency and
magnitude of heavy rainfall events have increased in that state. Madison, for example, had nine days with
three inches of precipitation in the last decade, compared to three such days in the decade with the most such
storms out of the five previous decades.8
8
3. FLOODS AND OTHER IMPACTS
E
Extreme storms matter in Michigan because of their
An increase in extreme storms in Michigan
impacts—most importantly, destructive flooding.
is important because they can lead to
One particular consequence of flooding in Michigan
can be overflows of outdated combined sewer/
destructive flooding, harm to people’s
stormwater systems, which handle both sewage and
health, power outages, and adverse effects
stormwater runoff in a single system. When runoff is
on transportation and agriculture.
heavy enough, the systems can overflow, potentially
contaminating nearby drinking water supplies and
cause public health problems. A new analysis done
for this report, detailed below, links large combined sewer overflows (CSOs) with extreme storms, illustrating
how the increase in large storms documented in this report is a risk to the health of Michigan residents.
FLOODS
Floods are to Michigan and other states in the Midwest what hurricanes are to the Atlantic coast areas—the
most destructive type of regularly occurring natural disaster in the region. Across the United States, flooding
is the second most costly type of natural disaster, ranking behind only hurricanes and ahead of drought,
earthquakes, coastal disasters (including storm surges, coastal flooding, and erosion), tornadoes, and other
types of natural disasters.9
An increased frequency of extreme storms, as documented for Michigan in this report, can increase soil
moisture and thereby reduce the water holding capacity of the soil for subsequent storms. The result is that
more rainfall becomes surface runoff, which can cause flooding.10
2013 Flooding
In 2013, the year with the fourth most two-inches-plus storms in Michigan in the past half century, storms
in April 2013 caused flooding so extensive that it led to a federal disaster designation covering 16 counties
in the state.11 This disaster illustrates well the impacts of the heaviest precipitation events. On April 10, four
Michigan weather stations had storms of more than two inches that set record amounts of rainfall for the date,
and helped create the conditions for the flooding of later in the month.12 Then, on April 18, eight Michigan
stations had record-breaking rainfall of two inches or more, and on April 19, one more did.13 Fortunately,
another 3 to 4 inches of rain forecast for April 20 did not materialize.14 Still, much of southern Michigan
received a total of more than eight inches of rain in the month.15 Widespread flooding resulted, with the Grand
River in Grand Rapids peaking at its highest level ever, nearly two feet above the previous record level reached
in 1985.16
Just one of the 16 counties covered by the federal disaster designation—Kent County—had $10 million in
damages.17 Just one action by the City of Grand Rapids to protect its citizens, the emergency construction as
the 2013 flooding was underway of a wall to keep floodwaters out of the city’s wastewater treatment plant,
cost $700,000.18 The Grand River ended up falling just short of overtopping the emergency wall, averting
flooding that could have put the wastewater plant out of business for perhaps a month or more, but 435
million gallons of partially-treated sewage still overflowed from the plant and into the river.19
“Weathering models for the future suggest that rain events
like this one will come more frequently and with greater
severity than before.”
George Heartwell, Mayor of Grand Rapids20
9
2008 Flooding
Of the 50 years covered by the precipitation analysis done for this report, the year with the most extreme
storms was 2008, for both Michigan as a whole and southern Michigan. That year’s extreme storms were
concentrated in the first half of June, and were destructive enough to have 11 Michigan counties designated by
the federal government as a major disaster area.21 From June 1 through June 15, parts of the northern Lower
Peninsula had 8 inches or more of rain, and parts of southern Michigan had 6 inches or more. The heaviest
storms were on June 12, when two of the Michigan stations analyzed for this report each had their highest
rainfall amounts for any day in the past 50 years—over 7 inches at Manistee, and over 5 inches at Lake City.
Some other areas in Manistee and Mason counties had as much as 11 inches of rain over six hours. Trees were
knocked down, buildings damaged, parts of roads were washed away, and some bridges were made unstable
or impassable.22 Two people were drowned when they drove off a washed-out road and into a creek, where
their car sank.23 Flooding on the Big Sable and Little Manistee rivers exceeded a 500-year flood event, and on
the Pine River was between a 200- and 500-year flood event. Ludington State Park was evacuated and closed
for four days for fear of a possible collapse of the dam from the high water and because of flooding in the
campground.24
The June 2008 extreme storms and flooding in Michigan were part of a region-wide episode of extreme
storms and flooding that, in all states, caused a staggering $16.2 billion (in 2013 dollars) in damages, with
even greater rainfall totals and worse flooding in several other states.25 Figure 6 below shows rainfall totals
across the Midwest for the first half of June, which in some places exceeded 12 inches. The most devastating
flooding across the region was precisely in these areas or just downstream of them.26 This illustrates one
of the significant dangers of more frequent extreme storms—when they occur in close succession, the first
storms can fully saturate the ground, so the later storms are especially likely to lead to flooding.
Total Precipitation, June 1–15, 2008
Figure 6. Total precipitation in inches, June 1-15, 2008. Source: Midwestern Regional Climate Center.27
10
1986 Flooding
Michigan’s second-place year for extreme storms was 1986, when those storms caused “the worst flooding
event ever recorded in the state,” according to the National Weather Service (NWS).28 Over three days in
September of that year, 6 to as much as 11 inches of rain fell on the Saginaw Valley and the Thumb, causing
extensive flooding. The town of Vassar was hardest hit—“inundated,” the NWS said. There, the Cass River
rose to nearly 25 feet, five times its normal height and more than 10 feet above flood stage.29 There also was
substantial flooding in Saginaw, Midland, and Bay City. Damages were estimated at $400 to $500 million, 30
counties were declared a federal disaster area, and 10 people in the state were killed.
Infrastructure damage from the Great Flood of 1986 included the failure of 14 dams, flooding or structural
damage to about 30,000 homes, and failures of four bridges on primary highways and hundreds of secondary
road bridges and culverts, making 3,600 miles of roadway impassable. Agricultural damage was substantial,
especially in the Saginaw River basin, where dikes were breached and thousands of acres of crops were
ruined. Altogether, more than 10% of the state’s crop land was affected, and more than 1,200 farm-related
structures were flooded.30
EFFECTS ON PUBLIC HEALTH
Extreme storms can kill people. For example, the Great Flood of 1986 led to at least 10 deaths in Michigan—a
hunter, a woman who drove her car off a road and into a flooded river, two children swept away by a flooded
stream, two boaters who drowned, and two men who were electrocuted while using sump pumps to empty
flooded buildings. Two farmers, seeing the loss of all their crops, committed suicide.31
More often, though, extreme storms cause a myriad of public health problems, as summarized below.
Contamination of Drinking Water
Consumption or exposure to contaminated water can cause illnesses and even deaths. According to a U.S.
government report, floods can lead to transmission of water-borne diseases, both directly by contaminating
freshwater sources with untreated or partially treated sewage, and indirectly by causing the breakdown of
water supply and sewage treatment infrastructure facilities.32 More than 100 different types of waterborne
bacteria, viruses, and protozoa can enter drinking water systems and cause infections in people.33 The
importance of floods—and the storms that cause them—are underscored by calculations that over half of all
waterborne disease outbreaks in the United States are triggered by storms in the top 10% of precipitation
magnitude.34
An extreme example was in Milwaukee in 1993, following the city’s heaviest rainfall in half a century,
which caused flooding believed to have washed a disease-causing parasite into Lake Michigan, contaminating
water used by city residents for drinking water. The result was the largest drinking-water contamination ever
documented in the United States, with 54 people killed and over 400,000 sickened. This outbreak also led to
$31.7 million in medical costs and $64.6 million in productivity losses.35
Although adequate data are lacking on the extent of waterborne disease in the country, it is believed to be a
growing problem.36 By increasing the frequency of extreme storms, climate change is expected to make water
contamination an even more serious problem in the future.37
Combined Sewer Overflows
In Michigan and other midwestern states, health-threatening water quality problems often stem from
combined sewer systems, an older type of systems which carry both stormwater and sewage in the same
pipes. Michigan has 46 combined sewer systems, the third-largest total in the nation.38 Combined sewer
systems, to avoid backing sewage and stormwater into basements and onto streets, are designed to overflow
when stormwater exceeds their capacities, discharging untreated sewage and stormwater directly to nearby
water bodies. These are called combined sewer overflows (CSOs), which can spread untreated human and
industrial wastes containing dangerous pollutants, including bacteria, toxic chemicals, pesticides, oil and
grease, sediment, nutrients, and trash, all of which can harm water quality.39 People can become sick by
drinking CSO-contaminated water, eating contaminated shellfish, or from contact with contaminated water
either in flooded streets and basements or when recreating in downstream water bodies.40
“It is common for local rivers and streams to be
considered dangerous to human health after heavy
rains due to CSO pollution.”
U.S. Environmental Protection Agency41
11
Extreme storms also can cause failures worse than designed discharges from an overtaxed combined
sewer system. In the Michigan flooding of June 2008, excessive stormwater caused Ludington’s sewer main
and a 50-feet section of a road to collapse, sending 90% of the city’s raw sewage flowing directly into Pere
Marquette Lake for 60 hours. An estimated 15 million gallons of untreated sewage and 10 million gallons of
storm water went into the lake. The health department closed three public beaches and three boat launches
near Ludington.42
New Analysis of CSOs and Storms
For this report, a new analysis was made of how many of a representative sample of recent combined sewer
overflows in Michigan were linked to this report’s definition of an extreme storm—one with two inches or
more of precipitation in a single day. Of the 17 CSOs in the sample, 13—or 76 percent—were associated with
extreme storms.
The analysis is based on data supplied to the authors of this report by the Michigan Department of
Environmental Quality (MDEQ).43 The analysis covers the largest reported single overflows for each of the 17
wastewater treatment plants that had at least one combined sewer overflow event with 50 million gallons or
more of overflow per event in Michigan in 2008 through 2012, as reported by MDEQ, and information on local
precipitation amounts associated with those CSO events, as compiled by Rocky Mountain Climate Organization
(RMCO) from daily precipitation records for the weather stations closest to the plants. (There were a total of
292 Michigan CSOs of this size in 2008-2012, and only the single largest event in each system was analyzed.)
As stated above, of these 17 representative large CSOs, 13 were caused at least in part by storms of two
inches or more of precipitation in a day (sometimes in conjunction with other storms). This powerfully
illustrates how extreme storms in Michigan lead directly to CSOs and the public health effects they can
cause, and how continuing increases in the frequency of extreme storms can increase risks to public health in
Michigan.
The results of this analysis are shown in Table 4 on the next page.
Of the largest combined sewer overflows in
recent years at 17 Michigan sewer districts,
three-quarters were associated with storms
of more than two inches of rainfall in a day.
12
Locally Largest Combined Sewer Overflows in Michigan
And Associated Rain Storms, 2008-2011
Overflow
(millions of
gallons)
Dates
Detroit
8,817
Nov. 27–Dec. 9, 2011
2.1 on Nov. 23, then 5.0 over Nov.
27–Dec. 9 (single-day high of 1.6).
Southeastern Oakland
County Sewage
Disposal System
1,304
May 25–27, 2011
3.0 on May 25-26.
Southgate/ Wyandotte
461
Nov. 27–Dec. 2, 2011
2.1 on Nov. 23, then 3.8 over Nov. 27–
Dec. 2 (single-day high of 1.6).
Saginaw
375
Aug. 10–11, 2012
2 on Aug. 10, then 3 the next day.
Dearborn
361
Jun. 11–21, 2009
3.7 on June 11.
8 1/2 Mile Relief Drain
Drainage District
308
May 25–27, 2011
3.5 on May 26.
Milk River Intercounty
Drainage Board
270
May 25–28, 2011
3.3 on May 26.
Bay City
164
Apr. 26–May 3, 2009
1.6 on Apr. 26.
South Macomb
Sanitary District
153
Mar. 7–9, 2009
1.3 on March 8, then 0.7 the next day.
Lansing
138
Sep. 12 –14, 2008
2.7 on Sep. 13, then 2.7 the next day.
Wayne County/
Redford/Livonia
118
May 26, 2011
2.6 on May 26.
Niles
90
Jan. 7–15, 2008
0.9 on Jan. 7, then 1.7 the next day.
Grand Rapids
80
July 2–3, 2008
3.2 on July 2.
North Houghton Co.
Water and Sewage
Authority
58
Apr. 7–30, 2008
0.3 maximum daily totals (twice)
during the CSO event.
Wayne County/
Dearborn Heights
58
May 26, 2011
2.6 on May 26.
Bloomfield Twp/
Bloomfield Hills/
Birmingham
54
Sept. 13–15, 2008
3.4 on Sept. 14.
Wayne County/Inkster
53
Jun. 5–6, 2010
3.3 on June 6.
Wastewater Plant
Precipitation
(inches)
Table 4. Combined sewer overflows (CSOs) with the largest outflows in selected Michigan wastewater treatment systems from 2008
through 2012, and associated rainfall totals. Listed for each system with a CSO of at least 50 million gallons of outflow in 2008-2012
is the single largest such event, and associated precipitation information for the closest Global Historical Climatology Network weather
station. Because precipitation records typically are taken in the morning and cover the previous 24 hours, the precipitation totals shown
for a date usually cover a portion of that day and a portion of the previous day. Data sources: Michigan Department of Environmental
Quality and NOAA.44
13
Threats to Private Wells
Michigan has more than one million households, more than any other state, served by private drinking water
wells.45 Private wells are at risk of contamination from flooding, which can cause health problems for people
drinking from them.46 The Michigan Department of Environmental Quality urges residents whose private water
wells have been exposed to flooding to immediately refrain from using the water until it has been tested
and found to be free of coliform bacteria, which represents an acute health threat, as floodwater can contain
bacterial contaminants such as fecal coliform and Escherichia coli (commonly known as E. coli) bacteria, which
represent an acute health risk. Floodwater also can contain other contaminants from sewage systems and
other sources, as well as fertilizers, pesticides, and other chemicals.47
Contamination of the Great Lakes
Contaminants washed into the Great Lakes by extreme precipitation can cause dangerous levels of both
bacteria and algae.
Michigan has more than 600 public beaches stretching along more than 3,200 miles. In 2012, according to
the Natural Resources Defense Council’s annual Testing the Waters report on water quality at public beaches
across the nation, 20% of Michigan beaches had at least one water sample exceed state water quality
standards, and there were a total of 324 instances in which Michigan beaches were closed or subject to public
health advisories (counting each such day at one beach as one instance).48 Contamination of water quality at
beaches in Michigan, as well as throughout the Great Lakes region, often results from extreme precipitation.
Of beaches studied in 12 Great Lakes cities, closures in eight, including Detroit, were significantly linked to
heavy storms the prior day.49
Extreme storms also are one of the major factors that can cause the layers of green, toxic algae that have
covered Lake Erie in recent years. In 2011, a record-setting algae bloom covered 2,000 square miles, from
Detroit to Cleveland. A team of scientists recently identified its causes:
• long-standing agricultural practices that regularly yield phosphorus runoff from farms;
• extreme precipitation that carried much more of the phosphorus than normal into the lake;
• and a reduction, caused by separate weather conditions, in the normal circulation of lake waters.
The study also found “that all of these factors are consistent with expected future conditions.” Unless
something is done, “we can therefore expect this bloom to indeed be a harbinger of future blooms in Lake
Erie.” For March through June, the critical months when agricultural run-off of phosphorus into Lake Erie
can set up algal blooms, the scientists projected that with a high level of future emissions of heat-trapping
pollution storms of about 1.2 inches or more per day could be twice as common by 2080-2099 as in 19862005.50
These conclusions also underscore the importance of the conclusion from the original research done for this
report that spring has had the largest increase of any season in the frequency of Michigan extreme storms
(see Table 3 on page 8.)
Some of algae blooms in the Great Lakes are harmless, but when the blooming organisms contain toxins,
other noxious chemicals, or pathogens, they can cause the death of nearby fish and foul up nearby coastlines,
and produce harmful conditions to aquatic life as well as humans.51 In people, consumption of large amounts
of harmful algae can result in muscle cramps, twitching, paralysis, and cardiac or respiratory failure.52
Indoor Air Pollution
Flooding in homes and other buildings can create breeding grounds for mold, viruses, and bacteria, which can
cause disease, trigger allergic reactions, and pose health risks long after the flood.53 Basements, of course, are
particularly susceptible to flooding. In Chicago, some of the largest economic impacts of extreme precipitation
in the Chicago area in recent years have been property damage from basement flooding, and city officials
are now aware that more frequent and destructive basement flooding could result from climate change.54 In
Michigan, where many communities have long had problems with basement flooding, this could be an issue,
too.
OTHER IMPACTS
Power Outages
The major threat to the reliable delivery of electricity to customers is from storms, especially from storms
accompanied by lightning strikes or high winds and from power line interruptions from heavy snowfalls.55
Such storms can cause power outages. The extreme storms in southern Michigan in April 2013 (see page 9)
caused a loss of power to nearly 100,000 customers of DTE Energy that lasted up to three days.56 Nationwide
14
since 2000, the number of storm-related power outages has increased, increasing repair and other costs for
utilities and consumers and causing economy-wide costs from work interruptions, lost productivity, and other
consequences. National costs have been estimated at $20 to $55 billion annually.57
Transportation
Transportation, vital both to the needs and convenience of individuals and to operation of Michigan’s
economy, can be disrupted by extreme storms, which can flood and wash out highways, roads, and bridges
and disrupt air and rail travel.58 According to an article written by staff members of the state’s Department
of Transportation, in Michigan, closure of a typical freeway for an hour can cost $200,000 in lost economic
activity, and the closure of all state roadways for a day would cost the state’s economy about $250 million.59
In the Michigan flooding of June 2008, numerous roads in the region were affected. A quarter mile of the
highway between Manistee and Ludington was washed out, forcing an 80-mile detour and costing $250,000
to rebuild. In Mason County, stretches of 42 roads were closed, and in Manistee County nine were. Other road
washouts occurred in Missaukee, Wexford, and Osceola counties.60
A greater tale of destruction comes from the Chicago area, where a record-breaking 24-hour rainstorm in
July 1996 caused widespread flash flooding across the metro area, damaging highways, roads, and railroads,
keeping many commuters from being able to reach Chicago for up to three days, and delaying or rerouting
more than 300 freight trains.61
Agriculture
Agriculture can be harmed by extreme storms in several ways. Spring storms can delay crop planting, field
flooding can cause crop losses, heavy rainfall can create excess soil moisture and erode soil, and storms with
strong winds can flatten crops.62 In Michigan, of the $400 million to $500 million in damages caused by the
Great Flood of 1986, about $120 million was from damages to crops, which were near harvest time.63 Another
example of agricultural damage from extreme storms comes from the July 1996 downpours in and around
Chicago, which, although centered on the metropolitan area, reduced crop yields in surrounding rural areas
enough to cause a $67 million loss of farm income.64
15
4. MORE POLLUTION, MORE STORMS
T
The increase in extreme storms documented in
this report is part of a global increase in heavy
precipitation that scientists say stems from human
disruption of the natural climate. Scientists also
project that if emissions of heat-trapping pollution
continue to grow, further increases in large storms
will result, especially in the Midwest.65
Human-caused climate change has been
identified on global and national scales as
a cause of the types of increased extreme
precipitation documented here. Scientists
project that continued climate change will
lead to further increases in extreme storms,
including in Michigan.
ATTRIBUTION TO HUMAN-CAUSED
CLIMATE CHANGE
Human actions are already changing the climate, both through increases in temperatures and also through
related changes, including increases in extreme precipitation. That global temperatures are now higher and
that human activities are causing them are now well-established. In 2013, the Intergovernmental Panel on
Climate Change (IPCC) reported that, “It is extremely likely [a 95 to 100% probability] that human influence
has been the dominant cause of the observed warming since the mid-20th century.”66 According to both the
IPCC and a national climate assessment prepared by the U.S. government in 2014, natural factors would
have led to global cooling over the past 50 years, except those natural factors were trumped by heat-trapping
pollution.67
For years, scientists have pointed out that, under the laws of atmospheric physics, higher air temperatures
should lead to more extreme precipitation. This is because, as a result of “very basic physics,” warmer air
holds more moisture than cooler air does, increasing the likelihood for extreme precipitation when a storm
does occur in a hotter climate.68 Scientists therefore expect that temperature increases will lead to a larger
change in extreme precipitation than in median precipitation.69 Observations that this projected change is
underway—across the planet and in the United States have added to the confidence of scientists that human
influences are already changing Earth’s climate.70
“The increase in heavy precipitation events is associated
with an increase in water vapor, and the latter has been
attributed to human-induced warming.”
U.S. Climate Change Science Program71
In 2011, the first study was published demonstrating that human increases in heat-trapping gases have
contributed to increases in heavy precipitation.72 The authors based their conclusions on a “fingerprinting”
technique of climate scientists—using climate models and statistical analysis to separate the likely influences
of heat-trapping pollutants from natural climate variability. Comparing observed precipitation extremes at
6,000 Northern Hemisphere weather stations from 1951-1999 with simulated reconstructions for the same
time period by multiple climate models, they found that:
[H]uman-induced increases in greenhouse gases have contributed to the observed intensification of heavy
precipitation events found over approximately two-thirds of data-covered parts of Northern Hemisphere land
areas.73
Detecting a clear human role in changing extreme precipitation patterns at a smaller geographic scale is
much more difficult, and scientists have not yet reported any such conclusions for Michigan or any similarly
sized area in North America.74 However, with respect to flooding caused by extreme precipitation in the United
Kingdom in the fall of 2000, scientists performed such a “detection and attribution” study, which showed
that the likelihood of that flooding having occurred was approximately doubled by human influences on the
climate.75
16
The number of dots that can be connected is rising. Perhaps most importantly, as a leading climate scientist,
Kevin Trenberth, recently wrote, when the question is whether any particular extreme event is caused by
human-driven climate change, “The answer is that all weather events are affected by climate change because
the environment in which they occur is warmer and moister than it used to be.”76
A threshold may already have been crossed, so
that major floods perhaps now should no longer
be considered purely natural disasters but
instead mixed natural/unnatural disasters.
FUTURE EXTREME STORMS
The Intergovernmental Panel on Climate Changes projects with “high confidence” that across the world as
a whole extreme precipitation will increase with further climate change.77 According to both the IPCC and
the U.S. government’s 2014 national climate assessment, the higher the levels of future emissions of heattrapping gases, the greater the changes in heavy precipitation are projected to be.78
The Michigan Department of Natural Resources and the Upper Midwest and Great Lakes Landscape
Conservation Cooperative of the U.S. Department of the Interior, using methods developed by the Wisconsin
Focus on Energy, recently commissioned projections of future Michigan climatic conditions. These projections,
by the Center for Climatic Research of the Nelson Institute for Environmental Studies at the University of
Wisconsin-Madison, include projected increases in the frequency per decade of Michigan two-inches-plus
storms, based on three different possible levels of future emissions of heat-trapping pollution.79 The reported
results represent average projections from nine downscaled global climate models for each emission scenario.
Figure 7 on the next page shows the results from the low and medium-high emission scenarios (but not from
the third, intermediate scenario).
As Figure 7 shows, the projections are that with low future emissions, by mid-century the frequency of
Michigan two-inches-plus storms could be one or two storms per decade higher than in 1961-2000, and by
late in the century about two or three storms per decade higher, with variations in different parts of the state.
With medium-high future emissions, by mid-century the increases could instead be about one to three storms
per decade and by late in the century about three to six storms per decade. However, current climate models
are not as reliable in projecting the frequency of extreme events as they are in projecting changes in average
conditions, and they also appear to generally underestimate extreme precipitation.80 (For comparison, the
data on actual occurrences of extreme storms in Michigan presented in Section 2, when translated into terms
comparable to those shown in Figure 7, reveal that the first years of this century (2000-2013) have already
seen an increase of about two storms per decade compared to a 1961-2000 baseline.) The projections shown
in Figure 7 therefore should be taken as illustrations of possible future conditions, not as firm predictions. The
important point from these projections is that the frequency of extreme storms in Michigan is expected to
increase more if future emissions in heat-trapping pollution are higher, and less if future emissions are lower.
On this point, the Michigan projections are strongly consistent with other projections, nationally and globally.81
The major role that future levels of heat-trapping pollutants will play in determining the future extent of
heavy storms illustrates how important it is to reduce emissions to avoid unacceptable climate changes. The
good news is that with new policies designed to reduce heat-trapping pollution, we can, in fact, realize a better
future—if we choose to. (See Section 5.)
17
Projected Changes in Decadal Frequency of Michigan 2-Inches-Plus Storms
A. 2046-2065
Low Emissions
B. 2046-2065
Medium-High
Emissions
D. 2081-2100
Medium-High
Emissions
C. 2081-2100
Low Emissions
Change
in number
per
decade
7
3
6
2
5
1
4
0
Figure 7. Projected changes in the frequency of Michigan two-inches-plus storms, in the average number of storms per decade
compared to 1961-2000. Averages of downscaled results from nine global climate models each for low and for medium-high
future emissions.82 Source: Center for Climatic Research, Nelson Institute for Environmental Studies, University of WisconsinMadison.83
18
5. ACTIONS TO ADDRESS EXTREME STORMS
T
To address the increase in extreme storms and
floods, Michigan can both prepare for those events
and limit its emissions to do its part to reduce the
future severity of those events. Actions by both the
state and local governments are important, and will
be most effective if undertaken with a framework
of national (and global) actions and in concert with
actions by the private sector.
State and local governments and others
can undertake both climate preparedness
actions to reduce the adverse effects
of more extreme storms, and emission
reductions to limit future increases in
extreme storms.
CLIMATE PREPAREDNESS
Climate change preparedness (or adaptation), in the words of a report by the National Academy of Sciences,
involves “deciding how to cope with climate changes that we cannot, or do not, avoid so that possible
disruptions and damages to society, economies, and the environment are minimized and—where possible—so
that impacts are converted into opportunities for the country and its citizens.”84 The central recommendation in
that National Academy report is that all decision makers—in national, state, tribal, and local governments and
in the private sector, should identify their vulnerabilities to climate change impacts and the adaptation actions
that would make them more resilient to current and projected impacts.85
Key steps are assessing risks faced in a state or locality, and developing plans to address them.
Vulnerability Assessments
Many states have prepared statewide vulnerability assessments, of which an excellent example is that
prepared in Wisconsin in 2011 by the University of Wisconsin-Madison, the Wisconsin Department of Natural
Resources, and others.86 However, no comprehensive statewide assessment of climate change impacts has
been prepared specifically focused on Michigan’s vulnerabilities, although the Michigan Climate Action Council
(see below), unanimously recommended that: “The state of Michigan should undertake a comprehensive
planning effort to assess and address the state’s vulnerability to climate change and adaptation
opportunities.”87 Nor has a focused assessment been prepared of the Michigan impacts of a continuing increase
in extreme precipitation in the state.
However, state agencies are involved in the Michigan Climate Coalition (MCC), founded in 2010 to gather
stakeholders from across Michigan to help tackle climate change impacts. The MCC is sponsored by Michigan
State University with in-kind support from the Michigan Department of Environmental Quality to facilitate
climate adaptation in the state by tracking climate-related projects, translating technical reports into more
user-accessible information, and identifying research gaps to further target. The MCC includes members
from the private, public, and nonprofit sectors in Michigan, including the departments of Natural Resources,
Environmental Quality, Agriculture, and Transportation; the University of Michigan and Michigan State
University; and nonprofit organizations.88
Apparently the only systemic assessment of climate change vulnerabilities being conducted by the Michigan
state government is by the Michigan Department of Community Health (MDCH), which used a grant from the
federal Centers for Disease Control and Prevention to develop a strategic plan to address the public health
effects of climate change in Michigan.89 The plan explicitly recognizes “that more flooding and water pollution
due to heavy rainstorms” will result “in increased waterborne diseases outbreaks.”90 With additional federal
grants, the department is working to implement more detailed assessments and adaptation plans to address
the top risks.
Some local governments in the country have prepared their own assessments of local climate change risks.
An example is one prepared by a team of outside experts and local government staff for the City of Chicago
as part of its process in developing a local climate change action plan.91 Apparently the only Michigan example
of a comprehensive local climate change assessment and plan is from Grand Rapids, where the West Michigan
Environmental Action Council, in partnership with the Grand Rapids Office of Energy and Sustainability and
19
others in the community, prepared for the city government a Grand Rapids Climate Resiliency Report.92 The
report is a comprehensive overview of local vulnerabilities and actions that can be taken to address them.
Preparedness Planning and Management
Future climate impacts need to be factored into a range of plans and decision making processes employed
by state and local governments. Many states, but not Michigan, have completed comprehensive climate
adaptation plans, and others have developed sector-specific plans to address particular climate change
impacts.93 With respect to sector-specific plans relevant to increases in extreme storms, first and foremost,
these impacts need to be considered in disaster preparedness plans that are approved by the Federal
Emergency Management Agency (a requirement FEMA is in the process of developing).94 But decisions
regarding funding, financing, and designing an array of water, stormwater, and wastewater infrastructure,
transportation, energy, housing, and land use decisions would all benefit. Some states, like Wisconsin and
New York, have developed fairly detailed climate plans, but still fall short, as Michigan has done, in integrating
these findings into real decisions.
At the local level in Michigan, the City of Grand Rapids addresses climate change risks and preparedness in
its sustainability plan.95 The City of Ann Arbor is working to factor climate changes issues into the full range of
its various local plans.96 As just one example of a specific local policy, the city gives residents credits on their
utility bills for green infrastructure measures that reduce stormwater runoff from their property.97
Some of the most important actions in Michigan to reduce the risks from more extreme storms are those
that lessen the chances of combined sewer overflows. With respect to CSOs, some examples of the progress
being made are:
• By 2011, Michigan communities had avoided 77% of the number of CSOs that occurred in 1988, and
additional control plans measures are planned to eliminate other CSOs, primarily the installation of
retention basins to capture and hold combined sewage and rain water that otherwise would overflow into
surface waters.98
• Detroit, a historically major contributor to CSO events, is subject to a special phased Long Term Control
Plan.99 Work completed in 2005 at a cost of $166.5 million dollars has achieved significant reductions in
CSO volumes.100
• Once Lansing’s CSO control plan, adopted in 1991, is completed, 1.65 billion gallons of combined sewage
should be prevented from release into the Grand and Red Cedar Rivers.101
Doubtless, though, more actions than those now underway will be needed to prevent future CSOs, in large
part because current remedies rarely (perhaps never) are sized to prevent overflows from larger storms
anticipated due to climate change.
Often the best way to avoid runoff-related pollution and overburdening water infrastructure is to reduce the
volume of stormwater flowing to the storm drains. Green infrastructure restores or mimics natural conditions,
so rainwater can go into the soil or evaporate into the air rather than going down drains. Examples of green
infrastructure techniques are using porous pavement materials and planting rooftops with vegetation.102
The City of Grand Rapids, for example, has installed at its water treatment facility a rain garden which has
successfully captured all of the stormwater from major storms, preventing the stormwater from entering
and affecting the treatment facility, at a cost of only about half what conventional infrastructure would have
cost.103
EMISSION REDUCTIONS
Holding down emissions of heat-trapping pollution reduces the extent of climate change, which fuels increases
in extreme storms; so emission reduction actions are an important way to limit the worst storms. Across the
nation, many state and local governments have adopted climate initiatives and energy policies that reduce
emissions.104
A 2008 Michigan law, the Clean, Renewable and Efficient Energy Act, established a Renewable Energy
Standard requiring electric utilities to use renewable energy to produce at least 10 percent of their electricity
by 2015, or to negotiate the equivalent using tradable renewable energy certificates. The state’s two largest
utilities, Consumers Energy Company and DTE Energy, must achieve higher targets. The law also included an
Energy Optimization (energy efficiency) standard requiring natural gas and electric utilities to reduce overall
energy usage by specified targets. For 2012, utilities exceeded the law’s targets for that year by about 25%,
which will lead to customer savings of about $936 million, compared to utility expenditures of $246 million,
and reductions of about one million tons of heat-trapping carbon dioxide emissions.105
A Michigan Climate Action Plan was developed in 2009 by a stakeholder group, the Michigan Climate Action
Council, appointed by then-governor Jennifer Granholm.106 The plan includes measures to reduce emissions
20
of heat-trapping pollution, which, if fully implemented, could save Michigan residents an estimated $10
billion between 2009 and 2025.107 That plan, however, is not now being pursued. In 2013, Governor Rick
Snyder announced his vision for a “no regrets” energy future by 2025, calling for an emphasis on eliminating
energy waste, and replacing coal with newer, cleaner technologies, including the use of both natural gas and
renewable energy resources.108
Some local governments in Michigan are reducing emissions. The City of Grand Rapids has exceeded its
emission reductions goal by bringing down emissions from city operations by more than 7% below 1990
levels.109 With grants from the Michigan Department of Environmental Quality and in partnership with the
Michigan Suburbs Alliance, the smaller cities of Ypsilanti, Hazel Park, and Southgate each developed local
climate action plans to reduce emissions and a model process for small-city climate action.110
Although these and other examples show that some significant steps are being taken in Michigan to reduce
climate-changing pollution, more actions are needed for Michigan to do its part to reduce emissions enough to
avoid unacceptable impacts from extreme storms and other extreme events being fueled by climate change.
21
APPENDIX: RESEARCH METHODOLOGY
This Appendix details the sources and methodology for the RMCO analysis of precipitation data reported in
Section 2.
The authors analyzed all daily precipitation records for 1964 through 2013 from 37 Michigan weather
stations in the Global Historical Climatology Network (GHCN), using data obtained from the National Climatic
Data Center (NCDC) of the National Oceanic and Atmospheric Administration.111 The stations were selected
based on the completeness of the data records for the analyzed period and to be generally geographically
representative of the entire state of Michigan. With respect to data completeness, the stations have reported
data with no identified quality issues (see below) for an average of 95.2 percent of all days in the full analyzed
period. With respect to geographic representation, the stations were selected through the following process.
First, the state was divided into grids of one degree of latitude by one degree of longitude. Such grids have
previously been used in scientific studies to achieve geographic representativeness of weather stations in
an analysis.112 For the nine grids that were entirely or nearly entirely comprised of Michigan land area, two
stations per grid were selected for the analysis, one from the northern half of the grid and one from the
southern half of the gird. For the grids with less Michigan land area, one station per grid was selected, except
where the grid contained barely any Michigan land area or where no station with sufficient data was available.
In three cases, no station with sufficient data was available within a particular half of a grid (in one case) or
within a grid (in two cases), and in those cases stations just outside the half-grid or the grid were analyzed
instead. The 37 analyzed stations are listed below. (The station locations are shown in Figure 4 on page 5.)
Analyzed Weather Stations
Upper Peninsula
Northern Lower Peninsula
Southern Michigan
Champion Van Riper
Alpena Wastewater Plant
Albion
Bergland Dam
Charlevoix
Alma
Hancock Houghton County Airport Cheyboygan
Ann Arbor University of Michigan
Iron Mountain Kingsford
Wastewater
Battle Creek 5 NW
East Tawas
Manistique Wastewater Treatment Grayling
Plant
Big Rapids Wastewater Plant
Marquette
Lake City Experimental Farm
Dearborn
Munising
Manistee 3 SE
Gladwin
Sault Ste. Marie Sanderson Field
Maple City
Grand Ledge 1 NW
Stambaugh 2 SSE
West Branch 3 SE
Grand Rapids Ford International
Airport
Whitefish Point
Hart
Hillsdale
Kent City
Lapeer Wastewater Treatment
Plant
Port Huron
Saginaw MBS International
Airport
South Haven
Three Rivers
Yale
Table App-1. Weather stations used for this report’s analysis of daily precipitation records.
22
The time period analyzed was the 50 years from 1964 through 2013. Previous scientific analyses have
showed there was no significant trend to changes in very heavy precipitation prior to about 1970, either
across the contiguous United States or in the Midwest.113 As one team of scientists wrote after laboriously
analyzing daily precipitation data since 1893, “it is probably a paradox that so much effort was made to
collect, quality control, pre-process, and analyze data for the full 110 years, only to reveal that during the first
80 years no systematic changes occurred in very heavy precipitation frequency.”114
The daily precipitation data from GHCN stations are reviewed by NCDC for various possible errors, and
if the records for a day suggest the possibility of one, a quality flag is attached to that day’s data denoting
the type of potential error. In the analysis for this report, daily data with any type of embedded quality flag
were discarded from the analysis, and those days were treated as ones with missing data. This excluded data
deemed suspect for having failed any of several NCDC quality checks, which include checks for accumulation
totals, duplicates, gaps, internal consistency, streaks or frequent values, mega-consistency, naught values,
climatological outliers, lagged ranges, spatial consistency, temporal consistency, temperature too warm for
snow, and values beyond bounds. Data with measurement or source quality flags were not discarded, as those
flags do not relate to the accuracy of the data but instead to such matters as how values were calculated and
the sources for them. Missing data for particular days were addressed by converting the values for all reported
days of a year to equivalent values for 365.25 days.
Trends identified in the report are statistically significant with a 95% confidence level, based on an ordinary
least squares regression analysis, unless indicated otherwise.
23
NOTES
1. Midwest Regional Climate Center (MRCC), “Midwest
weekly highlights - August 11–17, 2014,” http://mrcc.isws.
illinois.edu/cliwatch/1408/week2.htm; Office of Congressman
John D. Dingell, “Michigan delegation pushes for emergency
disaster declaration,” 2014, http://dingell.house.gov/
press-release/michigan-delegation-pushes-emergencydisaster-declaration; Federal Emergency Management
Agency (FEMA), “President declares disaster for Michigan,”
news release, Sept. 25, 2014, http://www.fema.gov/newsrelease/2014/09/25/president-declares-disaster-michigan.
Change in the Midwest: Impacts, Risks, Vulnerability, and
Adaptation (Bloomington and Indianapolis: Indiana University
Press, 2012).
2. FEMA, “President declares disaster for Michigan,”
news release, June 18, 2013, http://www.fema.gov/newsrelease/2013/06/18/president-declares-disaster-michigan;
MRCC, “Midwest daily precipitation records for a specific
date,” http://mrcc.isws.illinois.edu/cliwatch/1304/records/
dailyprec1.html#Week2.
13. MRCC, “Midwest records” (see previous note).
11. FEMA, “President declares disaster for Michigan,”
news release, June 18, 2013, http://www.fema.gov/newsrelease/2013/06/18/president-declares-disaster-michigan.
12. MRCC, “Midwest daily precipitation records for a specific
date,” http://mrcc.isws.illinois.edu/cliwatch/1304/records/
dailyprec1.html#Week2.
14. M. Vande Bunte, “2013 Flood: Experts describe how close
Grand Rapids was to crippling floodwall breach,” mlive.com,
Jan. 5, 2014, http://www.mlive.com/news/grand-rapids/index.
ssf/2014/01/2013_flood_experts_describe_ho.html.
15. W. Marino, “April 2013 climate summary for southwest
lower Michigan,” NWS, 2013, http://www.crh.noaa.gov/
images/grr/climate/CS201304.pdf.
3. Intergovernmental Panel on Climate Change (IPCC),
“Summary for policymakers,” L. Alexander and others,
authors, p. 13, in IPCC, Climate Change 2013: The Physical
Science Basis, T. F. Stocker and others, editors (Cambridge,
U.K., and New York: Cambridge University Press, 2013),
http://www.climatechange2013.org/images/uploads/WGIAR5SPM_Approved27Sep2013.pdf; J. Walsh and others,
“Chapter 2: Our changing climate,” p. 23, in U.S. Global
Change Research Program (USGCRP), Climate Change
Impacts in the United States: The Third National Climate
Assessment, J. M. Melillo, T. C. Richmond, and G. W. Yohe,
editors (Washington: USGCRP, 2014), available at http://
nca2014.globalchange.gov/downloads.
16. Associated Press, “Mayor: Grand Rapids avoids disaster
in downtown floods,” Detroit News, Apr. 22, 2013, http://www.
detroitnews.com/article/20130422/METRO/304220359.
17. M. Vande Bunte, “By the dollars: A look at the damage
caused by the 2013 Flood,” mlive.com, Jan. 5, 2014, http://
www.mlive.com/news/grand-rapids/index.ssf/2014/01/by_the_
dollars_a_look_at_the_d.html.
18. Vande Bunte, “By the dollars” (see previous note).
19. M. Vande Bunte, “How quickly Grand Rapids could have
lost its sewage plant in 2013 Flood,” mlive.com, Jan. 8, 2014,
http://www.mlive.com/news/grand-rapids/index.ssf/2014/01/
how_quickly_grand_rapids_could.html.
4. National Weather Service (NWS), National Oceanic
and Atmospheric Administration (NOAA), “National hazard
statistics,” http://www.nws.noaa.gov/os/hazstats.shtml;
T. C. Peterson and others, “Why weather and climate
extremes matter,” p. 16, in U.S. Climate Change Science
Program (USCCSP), Weather and Climate Extremes in
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Hawaii, Caribbean, and U.S. Pacific Islands, T. R. Karl and
others, editors (Washington: NOAA, 2008), http://downloads.
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20. G. Heartwell, “Mayor George Heartwell: What did we
learn from the great flood of 2013? (guest column),” Grand
Rapids Press, Apr. 23, 2013, http://www.mlive.com/opinion/
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what_di.html#incart_river.
21. FEMA, “President declares major disaster for Michigan,”
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5. J. Walsh and others, “Appendix 3: Climate science
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22. S. Conradson, “Friday the 13th flooding in Northern
Michigan,” in Flood News for Michigan Floodplain Managers
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deq/lwm-nfip-summer-2008_248403_7.pdf.
6. Peterson, “Why extremes matter” (see note 4), p. 49.
7. S. Saunders, D. Findlay, and T. Easley, “Doubled trouble:
More midwestern extreme storms,” report of the Rocky
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23. MRCC, “Midwest weekly highlights - June 1–9, 2008,”
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24. Conradson, “Friday the 13th flooding” (see note 22), pp.
2-3, 25.
8. Wisconsin Initiative on Climate Change Impacts (WICCI),
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26. U.S. Geological Survey (USGS), Flooding in the United
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9. Peterson, “Why extremes matter” (see note 4), p. 18.
10. C. J. Anderson, “Local adaptation to changing flood
vulnerability in the Midwest,” in S. C. Pryor, editor, Climate
24
27. Image by MRCC, available in NCDC, “2008
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39. C. Kloss and C. Calarusse, Rooftops to Rivers: Green
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28. NWS Forecast Office, Detroit/Pontiac, MI, “Memorable
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gov/dtx/?n=dtxHistory2. Except as noted, all facts in this
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40. EPA, Screening Assessment (see note 38), p. 9.
41. EPA, Screening Assessment (see note 38), p. 8.
42. Conradson, “Friday the 13th flooding” (see note 22), pp.
2-3.
29. B. Deedler, NWS Forecast Office, Detroit/Pontiac, MI,
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43. K. Hozak, Southeast Michigan District Office, Water
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to M. Metzer, RMCO), Mar. 28, 2013.
30. All facts in this paragraph are from Michigan Water
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—Floods and droughts: Michigan,” http://mi.water.usgs.gov/
fdfloods.php.
44. CSO data from K. Hozak, Southeast Michigan District
Office, Water Resources Division, MDEQ, personal
communication (email to M. Metzer, RMCO), Mar. 28,
2013; precipitation analysis by the authors, using daily
precipitation data from the weather stations closest to
the identified wastewater treatment plants, obtained from
NCDC, “Daily Observational Data,” http://gis.ncdc.noaa.
gov/map/cdo/?thm=themeDaily; for documentation, see
NCDC, “GHCN (Global Historical Climatology Network) –
daily documentation,” ftp://ftp.ncdc.noaa.gov/pub/data/cdo/
documentation/GHCND_documentation.pdf.
31. All facts in this paragraph are from Deedler, “Thumbnail
sketch” (see note 29).
32. Peterson, “Why extremes matter” (see note 4), pp. 26–27.
33. J. A. Patz and others, “Climate change and waterborne
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47. MDEQ, “Caution urged for wells impacted by flooding,”
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85. NRC, Adapting to Impacts (see previous note), p. 15.
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70. Gutkowski, “Causes” (see previous note), pp. 89–90, 98.
26
88. Michigan Climate Coalition, “Michigan Climate Coalition,”
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105. Michigan Public Utilities Commission, 2013 Report on
the Implementation of P.A. 295 Utility Energy Optimization
Programs, 2013, http://www.michigan.gov/documents/
lara/2013_Energy_Optimization_Report_to_the_
Legislature_11_26_13_449360_7.pdf, and 2012 Report on
the Implementation of P.A. 295 Utility Energy Optimization
Programs, 2012, http://www.michigan.gov/documents/
mpsc/2012_EO_Report_404891_7.pdf.
90. MDCH, “Michigan climate and health adaptation plan,”
2012, p.2, http://www.michigan.gov/documents/mdch/MDCH_
climate_change_strategicPlan_final_1-24-2011__343856_7.
pdf.
91. K. Hayhoe and others, Climate Change and Chicago:
Projections and Potential Impacts (Chicago: City of
Chicago, 2007), available in several parts at http://www.
chicagoclimateaction.org/pages/research___reports/8.php.
106. Michigan Climate Action Council, “Climate action plan”
(see note 87).
92. West Michigan Environmental Action Council, “Grand
Rapids climate resiliency report,” 2013, available at https://
wmeac.org/climate-resiliency-report/.
107. Michigan Climate Action Council, “Climate action plan”
(see note 87).
108. State of Michigan, “Governor Snyder sets goals for ‘no
regrets’ energy future by 2025,” media release, Dec. 13,
2013, http://michigan.gov/snyder/0,4668,7-277--318423--,00.
html.
93. R. Bierbaum and others, “Chapter 28: Adaptation,” p. 676,
in USGCRP, Climate Change Impacts (see note 3).
94. FEMA, “State mitigation plan review guide: Highlights of
key concepts: Draft for external review,” 2014, http://www.
fema.gov/media-library-data/1410365092470-4dcaea7180
7b36f564f8e7841be4ff6b/State%20Mitigation%20Plan%20
Review%20Guide_Key%20Concepts.pdf.
109. City of Grand Rapids, “2011–2015 Sustainability plan”
(see note 95).
110. For example, City of Southgate, “Climate action plan”
(draft), 2012, https://s3.amazonaws.com/uploads.uservoice.
com/assets/042/979/461/original/CAP_SG_CAP_Report_
Draft_for_PC_Review_8_8_2012.pdf?AWSAccessKeyId=14
D6VH0N6B73PJ6VE382&Expires=1357925270&Signature=y
WdG4pCcbjH2GiUnel6lVRA4C64%3D, and other documents
available at Michigan Suburbs Alliance, “Climate Action
Planning,” http://climateplan.uservoice.com/forums/149518resources-how-are-you-creating-these-climate-acti.
95. City of Grand Rapids, Office of Energy and
Sustainability, “2011–2015 sustainability plan and progress
reports,” available at http://grcity.us/enterprise-services/
officeofenergyandsustainability/Pages/default.aspx.
96. J. M. Kershner, “Climate adaptation in the City of Ann
Arbor, Michigan,” in R. Gregg and others, The State of
Climate Change Adaptation in the Great Lakes Region
(Bainbridge Island, WA: EcoAdapt, 2012), pp. 103-105.
111. Data obtained from NCDC, “Daily Observational Data,”
http://gis.ncdc.noaa.gov/map/cdo/?thm=themeDaily; for
documentation, see NCDC, “GHCN (Global Historical
Climatology Network) – daily documentation,” ftp://ftp.
ncdc.noaa.gov/pub/data/cdo/documentation/GHCND_
documentation.pdf.
97. Kershner, “Adaptation in Ann Arbor” (see previous note),
pp. 103-105.
98. MDEQ, Combined Sewer Overflow (CSO) and Sanitary
Sewer Overflow (SSO) 2011 Annual Report (State of
Michigan, 2012), p. 21, http://www.michigan.gov/documents/
deq/wrd-cso-sso-2011-report_406303_7.pdf.
112. T. R. Karl and R. W. Knight, “Secular trends of
precipitation amount, frequency, and intensity in the United
States,” Bulletin of the American Meteorological Society,
vol. 79 (1998), pp. 231–241; P. Ya. Groisman and others,
“Contemporary changes of the hydrological cycle over
the contiguous United States: Trends derived from in situ
observations,” Journal of Hydrometeorology, vol. 5 (2004),
pp. 64–85; P. Ya. Groisman and others, “Trends in intense
precipitation in the climate record,” Journal of Climate, vol. 18
(2005), pp. 1326–1350.
99. MDEQ, Combined Sewer Overflow (CSO) &
Sanitary Sewer Overflow (SSO) 2007 Annual Report,
2008, http://www.michigan.gov/documents/deq/deq-wbcsossoreport07_243725_7.pdf, p. 17.
100. MDEQ, 2011 Annual Report (see note 98), pp.15– 17.
101. City of Lansing, “The CSO story,” http://www.lansingmi.
gov/pubserv/cso/the_cso_story.jsp; City of Lansing, “Greater
Lansing Go Green! initiative,” http://www.lansingmi.gov/
gogreen/.
113. Groisman, “Contemporary changes” (see previous note),
pp. 64-85; Groisman, “Trends in intense precipitation” (see
previous note), p. 1336.
102. N. Garrison and K. Hobbs, Rooftops to Rivers II: Green
Strategies for Controlling Stormwater and Combined Sewer
Overflows (New York: NRDC, 2011), http://www.nrdc.org/
water/pollution/rooftopsii/files/rooftopstoriversII.pdf.
114. Groisman, “Trends in intense precipitation” (see note
112), p. 1336.
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