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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]