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http://wwa.colorado.edu
Future climate risks for Colorado’s water
Findings and insights from the updated WWA-CWCB Climate
Change in Colorado report
AWRA Colorado – Lunch Presentation
October 28, 2014 – Denver Water
Jeff Lukas, Research Integration Specialist
CIRES Western Water Assessment
University of Colorado Boulder
http://wwa.colorado.edu
2014 revision of the 2008 Climate Change in
Colorado (2008) report
•
The observed record of Colorado’s climate
•
A primer on climate models, emissions scenarios,
and downscaling
•
Linking Colorado’s climate trends and events to
global climate change
•
Projections of Colorado’s climate for the mid-21st
century (~2050); implications for water resources
•
Incorporating climate change information into
assessment and planning
•
PDF available via http://wwa.colorado.edu or
http://cwcb.state.co.us/
http://wwa.colorado.edu
Traditional risk assessment for water supply
•
Estimate the probability of a particular outcome; i.e., 10%
chance that runoff will be <50% average any given year
•
Assumption of stationarity
http://wwa.colorado.edu
Colorado has warmed significantly, 2°F over the past 30 years
Observed
Figure ES-1 & 2-8
http://wwa.colorado.edu
Annual precipitation, statewide: No significant long-term trends
Observed
Not in report; see Fig. 2-6
http://wwa.colorado.edu
April 1 SWE low since 2000, but 30-yr & 50-yr trends not sig.
Observed
Figure 2-9
http://wwa.colorado.edu
Annual
streamflow in
major river
basins in CO:
No significant
trends
Observed
Figure 2-10
But runoff
timing has
shifted earlier
by 1-4 weeks,
due to
warming, duston-snow, lower
SWE since
2000
http://wwa.colorado.edu
Statewide summer Palmer Drought Index (PDSI): significant
trend towards more drought in past 30 years
Figure 2-11
Observed
http://wwa.colorado.edu
Multiple paleodroughts more severe and sustained than any
observed drought
Figure 2-15
http://wwa.colorado.edu
Long-term observed statewide climate trends
Heat waves
more frequent
Cold waves
less frequent
Frost-free season
longer
April 1 SWE
no significant trends
Annual streamflow
no significant trends
Snowmelt
earlier
Peak runoff timing
earlier
Palmer Drought Index
more drought
Heavy precipitation events no significant trends
Floods
no trends?
Observed
http://wwa.colorado.edu
Colorado observed warming: “in step with” global and regional
warming that has been linked to anthropogenic influences
Figure 4-3
http://wwa.colorado.edu
Global climate models (GCMs): supercomputer-based
representations of our knowledge of the climate system
Image: Nicolle Rager Fuller, NSF
http://wwa.colorado.edu
Different climate models will give you somewhat
different answers about the future climate
Colorado will be
3.5°F warmer by
2050
•
•
4°F
warmer
5°F
warmer
2.5°F
warmer
The group (ensemble) of latest model projections (>200
projections from >30 models) is collected in the CMIP5 archive
Previous-generation ensemble was CMIP3 used in 2008 report,
CRWAS, Joint Front Range Study, and Basin Study
http://wwa.colorado.edu
And multiple emissions scenarios, since we don’t know
how greenhouse gas emissions might evolve over time
Figure 3-3
http://wwa.colorado.edu
The resolution of the GCMs is too coarse to capture CO’s
mountains, so downscaling needed for hydrologic modeling
Figure 3-4
http://wwa.colorado.edu
Colorado continues to warm in all projections, by 2.5°F to 5°F
by 2050
CMIP5
shows
similar
warming
for CO
vs.CMIP3
37 model
projections under
RCP 4.5
Projected
Figure ES-1; Figure 5-1
http://wwa.colorado.edu
By 2050, typical year will be warmer than the
warmest years of the past century
Projected
Figure 5-2
http://wwa.colorado.edu
Higher RCP # (more GHG forcing) = more warming
12
Temperature departure/change,
°F
10
8
RCP 8.5
6
4
RCP 4.5
2
0
-2
-4
-6
1950 1960 1970 1980 1990 2000 2010 2020 2030 2040 2050 2060 2070
Projected
Adapted from Figure 5-2
http://wwa.colorado.edu
The projected warming alone will tend to have an overall drying
effect on natural and managed landscapes
Transpiration
Moisture losses from plants, soils,
water surface, and snowpack will
tend to increase with warming
•
Variation in streamflow is
driven mainly by
variability in annual
precipitation
•
Temperature, humidity,
and winds affect evapotranspiration (loss of
water from the surface
and vegetation)
Tendency towards
decreased snowfall,
snowmelt, and runoff
http://wwa.colorado.edu
Colorado statewide precipitation change by 2050 uncertain;
we’re between regions expected to get drier and wetter
+5%
CO a little
wetter in
CMIP5 vs.
CMIP3
0%
-5%
Projected
Figure ES-1; Figure 5-1
http://wwa.colorado.edu
Any future change in annual precipitation will be
difficult to detect as such against the high variability
Projected
Figure 5-4
http://wwa.colorado.edu
Seasonal: overall, projections suggest more winter,
but less summer precip
Projected
Figure 5-5
http://wwa.colorado.edu
General approach for projecting basin-scale changes to
hydrology -- as used in CRWAS, Basin Study, and new CMIP5based hydrology projections (USACE, NCAR, Reclamation, et al.)
Projected
Figure 5-19
http://wwa.colorado.edu
BCSD downscaling method imparts wettening effect on
CMIP5 in interior West; effect larger than with CMIP3
Projected
Figure 3-5
http://wwa.colorado.edu
Projected changes to key aspects of water resources
1) Annual streamflow – decreases in majority of projections
• Warming alone would reduce runoff, but uncertainty in
precipitation means a wide range of projected
outcomes, tending towards decreases
• More projections show decreases in San Juan and Rio
Grande basins
Projected
http://wwa.colorado.edu
For annual streamflow warming counterbalances precipitation
increases in many projections (Colorado R. near Cameo)
Figure 5-14
http://wwa.colorado.edu
New CMIP5-based streamflow projections using the Basin Study
methodology are shifted wetter than comparable CMIP3-based
Projected
Figure 5-13
http://wwa.colorado.edu
Projected streamflows for Colorado near Cameo (30-year running
averages): Broader range of possible futures vs. historical or paleo
90th
10th
Projected
Figure 5-15
http://wwa.colorado.edu
Risk assessment?
•
•
One could construct a PDF for each model run
But collapsing the ensemble of runs into a single
distribution is fraught with danger
http://wwa.colorado.edu
Projected changes to key aspects of water resources
2) Peak runoff timing – shifts earlier
• April 1 SWE and runoff timing more sensitive to
warming than annual streamflow is
• Peak runoff projected to shift another 1-3 weeks earlier
(+ dust-on-snow impact), decrease in late summer flows
Projected
http://wwa.colorado.edu
Observed vs. projected monthly runoff, Colorado near Cameo
Figure 5-16
Projected
http://wwa.colorado.edu
Projected changes to key aspects of water resources
3) Ag/outdoor water demand - increases
• Crop irrigation requirement and urban outdoor demand
projected to increase ~5-30% by mid-century (CMIP3)
• Due to both warming, and decrease in summer
precipitation in most projections
• Likely to be similar in CMIP5
Projected
http://wwa.colorado.edu
Summary - Projected climate and hydrology changes
Annual streamflow
Peak runoff timing
Crop water use
April 1 snowpack
Palmer Drought Index
Heat waves
Cold waves
Frost-free season
Wildfires
Projected
decreases in majority of projections
earlier in all projections
increases
decreases in most projections
more drought
more frequent
less frequent
longer
more frequent
http://wwa.colorado.edu
Planning for an uncertain climate future for Colorado
•
•
•
•
•
Continued warming will tend to push both supply and
demand in the wrong direction
Increased average precipitation could partly or mostly
compensate on the supply side
But systems will tend to bend/break during drought, and
future droughts will be more severe for a given
precipitation deficit
Traditional risk assessment not readily compatible with the
projections
Given the uncertainty in future precipitation and
streamflows, consider multiple scenarios that cover the
range of projected outcomes
http://wwa.colorado.edu
Scenario planning at Denver Water: Create several
narratives of plausible, multi-faceted futures
Source: M. Waage, Denver Water
(Marc Waage, Denver Water)
http://wwa.colorado.edu
Comments? Questions? Please contact me at
[email protected]