Download Udall - Western State Colorado University

An Overview of Climate and its
Relationship to Water in Colorado
29th Colorado Water Workshop
July 28-30, 2004
Gunnison, Colorado
Brad Udall
Managing Director
CU-NOAA Western Water Assessment
[email protected]
Western Water Assessment
http://sciencepolicy.colorado/wwa
What is the Western Water Assessment?
The mission of the Western Water
Assessment is to identify and characterize
regional vulnerabilities to climate variability
and change,
and,
to develop information, products and
processes to assist water-resource decisionmakers throughout the Intermountain West.
Why Western Water Assessment?
Help NOAA Consider and Implement Future
“Climate Services”, an analog to the National
Weather Service but Different…
Who?
University of Colorado Scientists
Legal and Policy
Snow and Geography
Water Quality
Economics
Climate Diagnostics Center Scientists
Policy
Climatologists
Snow Scientists
Paleoclimatologists
Colorado State University Scientists
Some Current Projects…
1. South Platte Regional Assessment Tool
2. Streamflow Reconstructions using Tree Rings
3. Climate Services Clearinghouse
4. Improved “Week 2” Streamflow Forecasts
5. Seasonal Forecasts for Drought Task Force
Long Term Climate Trends
Enormous Climate Variability
Source: NOAA
Climate Variability and
Colorado Compact
Issues??
The reconstruction of streamflow
at Lees Ferry is the
reconstruction most well-known
to western U.S. water managers.
.
Source: Woodhouse, 2003
Predicting Climate Variability in Colorado –
ENSO – Based Seasonal Forecasts
Source: Wolter Website, 2004
http://www.cdc.noaa.gov/people/klaus.wolter/SWcasts/index.html
New Research on Climate Variability
1. “Perfect Ocean for Drought” -Science Magazine,
2003
2. Atlantic Multidecadal Oscillation and Pacific
Decadal Oscillation - Proceedings of the National
Academy of Sciences, 2004
3. 2000 Years of Drought Variability in the Central
United States, American Meteorological Society,
1998
4. Declining Mountain Snowpack – Various
2003,2004
Perfect Ocean for Drought – La Nina and Warm Indian Ocean
Source: Hoerling, 2003
Perfect Ocean
for Drought -Models vs.
Actual 19982002
Source: Hoerling, 2003
2000 Years of Drought Variability in Central United States
•20th Century Droughts not Representative of the full range of droughts
over the last 2000 years
•Multidecadal Droughts of the late 13th and 16th Centuries were of
much greater duration and magnitude than 20th Century Droughts
Evidence suggests that droughts before the 13th Century were
decades in duration
•Droughts since the 13th Century have tended to be a decade or less in
duration, with exception of 16th Century drought
•Droughts of the 20th Century have been moderate severity and short
duration relative to entire record
Source: Woodhouse, Overpeck 1998
Reconstructed Upper Colorado
Streamflow
Drought Frequency
Brown = 1437-2002
Yellow = 1900-1999
Here, drought is
defined as one or
more consecutive
years below longterm average.
Source: Woodhouse, 2004
Reconstructed Upper Colorado River Streamflow, 1437-2002
smoothed with a 5-weight filter
Blue River
Source: Woodhouse, 2003
The early 20th century wet period does not appear matched in prior
centuries. However, drought similar to the 1950s drought have occurred.
Blue River
Source: Hoerling, 2003
Source: Woodhouse, 2003
Blue River
Presentation Slide w/o bottom
General Public – CU and NOAA
Source: Woodhouse, 2003
Declining Mountain Snowpack in Western North
America
• Much of the Mountain West has lost April 1 Snowpack in the
period 1950 to 1997
• Largest Decreases where temperature is mild, Northern CA and
Cascades
Source: Mote, et al, 2004
Less April 1 SWE Since 1950
Source: Mote, et al, 2004
1916 to 1997 Change in Timing of Peak
Snowpack
Source: Mote, et al, 2004
March 2004 Climate
Variability? Or
Something Else?
Source: Mote, et al, 2004
AMO
and
PDO
Climate Change – Albritton Congressional Testimony
•There is a natural greenhouse effect. It keeps the Earth warmer than it
would be otherwise. Confidence index = 10.
•Greenhouse gases are increasing in the atmosphere because of human
activities, and they are increasingly trapping more heat. Confidence index
= 9.
•There is a collective picture of a warming world, and human activities have
likely contributed. Confidence index = 7.5.
•A continued growth in greenhouse gases is projected to lead to very
significant increases in global temperatures and sea level. Confidence
index = 6.
•It is a complex planet and we have imperfect knowledge; so, prediction of
further details suffers. A more vigorous hydrological cycle is likely,
however other regional changes cannot be predicted reliably.
Confidence index = 4.
Albritton Summary…
•The climate change issue is a real one.
•The first signs of human-caused climate change have likely occurred.
•Some degree of further changes appears inevitable due to the CO2 already
in the atmosphere.
•Exactly which regions, how quickly, and the magnitude of climate change
are all hard to predict.
•Human-caused climate change would be slow to reverse.
More Vigorous Hydrologic Cycle – A Brief Technical Discussion
How can we have both more droughts and more floods?
–Increased temperatures means both more evaporation and more
precipitation
•Modeling suggests 1% to 2% increase in Evaporation per 2F increase
–Increased temperatures increase the ability of the atmosphere to
hold moisture
•Physics suggests that moisture holding ability increases by 7% per 2F
increase
–Rainfall intensity will increase at the 7% rate
•Rainfall is the ‘inverse’ of moisture holding ability – when
atmosphere cools it rains and loses moisture at this higher rate
–But because our new evap rate is much less than this new rainfall
rate, there will be decreases in number of rainfall events.
–And the increased evaporation means increased drying
Summary Climate Variability
Normal Climate Variability is Huge! Will likely swamp
climate change ‘signal’ for some time.
Current Ability to Predict Seasonally based on El Nino
conditions, with some skill.
Tree Rings provide good look back to 1400 or so.
Tree Rings indicate that we are likely to have more
variability in the future, not less.
By studying oceans we may have predictive breakthroughs in next few years.
Summary Climate Change
Science is Real, No Matter what you read.
Huge Uncertainties! Especially amount and timing of
warming.
At this time, not “actionable” for water managers.
Read IPCC, National Assessment, Skeptics; don’t rely on
the popular press ( with apologies to members of the 4th
Estate) – www.ipcc.ch
IPCC 4th Assessment Due 2006/07.
High Certainty of:
Warmer Temperatures
More Droughts and Floods
Earlier Runoff
Could be either wetter or drier
Graphic: Scientific American, 2004
Overall Summary
Get Used to Uncertainty!
Future may be very different from the past.
Be careful what you hope for: climate predictions may
lead to better operations, but at a price of increased
vulnerability.
Population pressures are more significant than
Variability or Change.
Order of concerns on a 10-year horizon: population
pressures, climate variability, climate change.
Order of concerns on a 100-year horizon: population
pressures,climate change, climate variability.
Overall Summary
The End…..
Get Used to Uncertainty!
Past may not be guide to the future
Be careful what you hope for: predictions lead to more
efficiency, but at a price of increased vulnerability.
Population pressures are more significant than Variability or
Change.
Order of concerns on a 10-year horizon: population pressures,
climate variability, climate change.
Order of concerns on a 100-year horizon: population
pressures,climate change, climate variability.
Bibliography
To Be Completed..
Additional Material
Antarctic Ice
Core Data Back
400,000 Years
Source: Petit, et al, 1999
1000 Year Temperature Data
Source: IPCC, 2001
IPCC Extreme Weather and Climate Events
Presentation Slide w/o bottom
General Public – CU and NOAA
Source: IPCC, 2001
CO2, CH4,
N20 Changes
Since 1000
AD
Source: IPCC, 2001
Key Messages for Water Managers from National Assessment
•
•
•
•
•
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Climate is not static and assumptions made about the future based on the climate of the recent past
may be inaccurate. Water managers should factor in the potential for climate change when
designing major new infrastructure.
Assumptions about the probability, frequency, and magnitude of extreme events should be
carefully reevaluated.
There is substantial stress on the water sector even in the absence of climate change. There are
numerous watersheds that are already over-appropriated,and new stresses are coming from
population dynamics,land use changes,and changes in international economies. In some areas,the
new demands associated with instream flow needs for habitat protection and Indian water rights
settlements may cause major shifts in water supply and water rights. Climate change may pose
additional stresses and could result in thresholds being reached earlier than currently anticipated.
Waiting for relative certainty about the nature of climate change before taking steps to reduce risks
in water supply management may prove far more costly than taking proactive steps now. (The
suggested risk-reducing or “no regrets”steps are those that would have other beneficial effects and
so are appropriate regardless of climate change.)
The types of changes encountered in the future may not be gradual in nature. Non-linearities and
surprises should be expected, even if they cannot be predicted.
The problems that are likely to result from climate change are intergenerational. Decisions made
today will commit future generations to certain outcomes. It is important to e valuate benefits of
projects over long time frames,and develop an educated citizenry.
Source: National Assessment, 1999