The Drying of the Colorado River Basin: Lessons from the past 25 years applied to the next 25 years. Blue Mesa Reservoir

Transcription

1 The Drying of the Colorado River Basin: Lessons from the past 25 years applied to the next 25 years Upper Colorado River Basin Water Forum: Bridging Science, Policy & Practice Colorado Mesa University November 7, 2018 Grand Junction, CO Blue Mesa Reservoir Animas River Brad Udall Senior Scientist/Scholar Colorado State University

2 In Large Parts of Colorado, 2018 was the Warmest and Driest in 123 Years of Record Keeping Water Year 2018 Precipitation Water Year 2018 Temperature

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4 Key Points Climate Change already impacting the basin Temps for sure, maybe precipitation Impacts will get Worse New Normal inadequate to convey challenges Aridification underway not a drought Plan on Heat! More and More as the Century Proceeds Shifting runoff patterns South (Dry) and North (Less Dry to Perhaps Wet) Earlier within-year runoff More WX Variability year to year, within-year Substantial Flow Reduction Risk Substantial Megadrought Risk Flood Risks Localized Likely Basin-wide -?? Higher Water Temperatures More Fires Opportunity for Change

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6 Climate Change Myths Climate is always changing It s the sun You said it was going to cool in the 1970s Winter Related It s cold and snowy We just set a cold record Can t predict weather, so can t predict climate Models are not any good 1930s were warmer... It s the Urban Heat Island Effect It s volcanoes

7 Colorado 2018 Temperature Records ~6x Difference Lesson: We can still set cold records

8 IPCC Special Report on 1.5 C Warming Warming is already ~1 C 1.5 C likely ~2040 at current rate Existing warming persist to 100s to 1000s of years Warming of 2 C worse than 1.5 C for human and natural systems Pathways to 1.5 C either require rapid and far reaching transitions or unprecedented large scale Carbon Dioxide Removal (CDR) Current Paris Targets if achieved get us to ~3.5 C My Take: Alarming but not Alarmist 1.5 or 2 C miss the mark need net 0 emissions as soon as possible (decades) Negative Emissions are Needed Regardless of the Pathway

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12 % of 20 th Century Mean Lee Ferry Flow 85 Most Severe Colorado River Low Flow Sequences Worst Sequence from each century % of 20th century mean Lee Ferry flow Lowest 21st Century Sequence Lowest 20th Century Sequence The Millennium Drought is very, very different from previous droughts in the historic record Length Length Of Low of Low Flow Sequence Years-- Years

13 Most Severe Colorado River Low Flow Sequences Worst Sequence from each century % of 20th century mean Lee Ferry flow % of 20 th Century Mean Lee Ferry Flow The outlier Represents 6 maf loss over 18 years relative to worst 20 th century drought Lowest 21st Century Sequence Lowest 20th Century Sequence Length of Years Length Of Low Flow Sequence -- Years

14 Millennium Drought is the worst drought in the gaged record maf Colorado River Flows 1950s Dry Drought 2000s Hot Drought ~ 20%/yr decline 10 Long-term trend, too 5 Annual Data Average Linear Trend Running Average Udall and Overpeck, WRR, 2017

15 Millennium Drought is the worst drought in the gaged record maf Colorado River Flows 1950s Dry Drought 2000s Hot Drought ~ 20%/yr decline 10 Long-term trend, too 5 Annual Data Average Linear Trend Running Average Lakes Powell and Mead have lost 50% of their volume maf a Mead + Powell Volume 1950s Dry Drought Only Lake Mead L. Powell Fills Both Reservoirs 2000s Hot Drought Udall and Overpeck, WRR, 2017

16 Millennium Drought Precipitation declines only partially explain ~ 2/3 of the loss inches Colorado River Basin Precipitation 1950s Dry Drought 2000s Hot Drought Annual Data Average Linear Trend Running Average Udall and Overpeck, WRR, 2017

17 Millennium Drought Precipitation declines only partially explain ~ 2/3 of the loss inches Colorado River Basin Precipitation 1950s Dry Drought 2000s Hot Drought Temperature increases explain the remainder ~ 1/3 of the loss Why? More Evaporation Thirstier Atmosphere Temperature-Induced Losses Now = ~6% 2050 = ~20% 2100 = ~35% F Annual Data Average Linear Trend Running Average Colorado River Basin Temperatures 1950s Dry Drought Annual Data Average Linear Trend Running Average Udall and Overpeck, WRR, s Hot Drought

18 Udall and Overpeck, WRR, 2017

19 Colorado River Future Flow Losses 0% 5% 10% Loss Range 0% +2% +4% Climate Change a combination of 1. For-Sure Temperature Rise -> Flow Losses 2. Not-Sure Precipitation Change -> Flow Gains or Losses Annual Flow Loss 15% 20% 25% 30% 35% 40% 45% 50% 55% 60% 65% Low Sensitivity Medium Sensitivity High Sensitivity +6% +8% +10% +12% +14% +16% +18% +20% +22% +24% +26% Precipitation Required to Equal Flow Loss 70% +28% 75% 80% Mid Century Moderate Emissions Mid Century High Emissions End Century Moderate Emissions +30% End Century High Emissions +32% Temperature Increase C

20 Temperature can be a major flow driver in addition to precipitation Since 1988 flows have been less than expected given winter precipitation Warm temperatures exacerbated modest precipitation deficits in the Millennium Drought

21 Model-based Study using Historical Data Model vs Natural Flow Model vs Natural Flow Model and Data Long-term Trend Analysis (-16.5% Decline) No Precipitation Trend Large Basin Warming >2.5 F Model Experiments Temperature De-trend Model Experiment 1950s vs 2000s Drought Analysis 2017 Forecast Analysis Precipitation Precipitation Temperature 4 Key Basins (Green + Blue) produce ~55% of all runoff

22 Findings ~50% of Decline due to Higher Temperatures More Evaporation ~50% of Decline due to Changing Precipitation Patterns Shift to less productive basins 4 Key Basins (Green + Blue) produce ~55% of all runoff

23 Denver Water Forecast Inflow vs Runoff 2018 Colorado River Headwaters snowpack peaked at 107% of normal South Platte River snowpack peaked at 85% of normal April through July Natural Streamflow Percent of Average South Platte at South Platte Blue River at Dillon Williams Fork Fraser at Winter Park May 1 NRCS Forecast 48% 99% 81% 99% Actual Natural Volume 38% 71% 71% 77% Source: Denver Water using Snotel and Gage Data

24 Denver Water Forecast Inflow vs Runoff 2018 Colorado River snowpack peaked at 107% of normal South Platte River snowpack peaked at 85% of normal April through July Natural Streamflow Percent of Average South Platte at South Platte Blue River at Dillon Williams Fork Fraser at Winter Park May 1 NRCS Forecast 48% 99% 81% 99% -10% -28% -10% -22% Actual Natural Volume 38% 71% 71% 77% Source: Denver Water

25 New Normal? It clearly will get hotter Expansion of the Wet/Dry Axis = more variability Hint of more occurrences of extreme wet than extreme dry Note: precipitation is not runoff Dave Pierce, Scripps

26 Aridification not a drought Declining Snowpack and earlier runoff Higher Temperatures Drying Soil Thirsty Atmosphere Moving storm tracks Shorter Winter/Longer Fall Greening? Megadrought? Aridity Index (P/PET) Changes Seager et al., 2018

27 Changing Precipitation Patterns: Dry South, Less Dry North Changes in Soil Moisture in 2100 Climate models: north is wetter, and south is drier Wet: Wind Rivers + Unita Mountains Dry: Most of Colorado Key: Where is the hinge point? CRB Mainstem critical

28 Evapotranspiration Increases in Natural Systems Now Future In the future, plants move up slope, increasing evapotranspiration. By 2100 ET increases by 28% and Kings River flows decline by 26%.

29 The Upper Colorado River Basin is Megadrought Country 1200 years of Colorado River flow thanks to tree rings Meko et al., (Geopysical Research Letters, 2007)

30 Cook Science In both Central Plains and Southwest, Multidecadal Drought Risk* exceeds 80% in 21 st Century * Defined as Drought lasting 35 or more years Percent Chance of Multi- Decadal Drought Risk, Southwest US

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32 P = +10% P = +20%

33 P = +10% Risk = 70% w/ P=+10% Risk = 35% w/ P=+20% P = +20%

34 Other Supporting Aridification Studies Response of Colorado River runoff to dust radiative forcing in snow Painter, et al., 2010 Hydrologic Sensitivities of Colorado River Runoff to changes in Precipitation and Temperature Vano et al., 2014 Climatology, Variability, and Trends in the U.S. Vapor Pressure Deficit, an Important Fire-Related Meteorological Quantity Seager et al, 2015 Running Dry: The US Southwest s Shift to a drier climate Prein et al., 2016 Relative impacts of mitigation, temperature, and precipitation on 21st-century megadrought risk in the American Southwest Ault et al., 2016 Evidence that Recent Warming is Reducing Upper Colorado River Flows McCabe et al., 2017 The Curious Case of Projected Twenty-First-Century Drying but Greening in the American West Mankin et al., 2017 Dramatic declines in snowpack in the western US Mote et al., 2018 The More Extreme Nature of North American Monsoon Precipitation in the Southwestern United States as Revealed by a Historical Climatology of Simulated Severe Weather Events Luong, et al., 2018 Vapor Pressure Deficit Trends = Atmosphere Thirst Seager et al., 2015 Snow Water Equivalent Trends Mote et al., 2018

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37 Progress (or lack) to Date with Managing Climate Change 2007 Interim Guidelines Appendix U Colorado Water Plan No real explicit climate change plans Basin Plans especially good DCP is all about climate change But only veiled acknowledgement No one stepping up on Greenhouse Gas Reductions not my responsibility doesn t cut it Water Community needs to lead Water Managers generally get the problem Some state agencies not so much

38 2026 UB-LB Renegotiations - 1 Should approach as if the worst will happen It will get worse as it warms, especially with large warming 75 maf/ 10 Year Obligation Understanding UB well under III (a) promised 7.5 maf CU Need Plan to cut both UB and LB demands if flows decline to 12/11/10 maf DCP promotes later recovery of saved water but also need bankruptcy Differing UB and LB responses New demands should not add to risk of existing demands No Net Demand Growth or Very Stringent Rules on when diversions allowed UB Lake Powell Insurance Account Some Resolution of III ( e ) Deals with unused UB Water

39 2026 UB-LB Renegotiations -2 Some resolution of Muni and Ag differing vulnerabilities to cut off Munis: can conserve, but need 100% reliability for some base supplies Ag: in many, but not all, cases less need for 100% reliability, but also have long-term issues with markets, labor, etc. Acknowledgement of CAP need for some water Can not be cut to zero unless horrendous conditions Not just a LB problem

40 Science to Assist Renegoitations New Hydrologies Stress Test s no longer appropriate Climate Change factor in known temp impact More Paleo Not optimistic about past climate model approaches to using precipitation Realistic Future Scenarios of all aspects Supplies, Demands, Rules Out of the Box Operational Rules Better Communication of Ongoing Work

41 Key Points Climate Change already impacting the basin Temps for sure, maybe precipitation Impacts will get Worse New Normal inadequate to convey challenges Aridification underway not a drought Plan on Heat! More and More as the Century Proceeds Shifting runoff patterns South (Dry) and North (Less Dry to Perhaps Wet) Earlier within-year runoff More WX Variability year to year, within-year Substantial Flow Reduction Risk Substantial Megadrought Risk Flood Risks Localized Likely Basin-wide -?? Higher Water Temperatures Fires Opportunity for Change

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43 Increasing Heat Content Everywhere 90% into the ocean

44 FOLU = Forestry, Other Land Use

45 Climate Change is Water Change Heat Drives the Water Cycle 1000 km3 evaporates daily from the oceans The Water Cycle mixes heat from areas of too much to too little As the Atmosphere Warms it Holds More Moisture: ~5F warming is 20% increase Heating Up the Earth (and uneven heating) results in Water Cycle changes More Evaporation, More Precipitation, More Moisture Changes in weather patterns Wet Wetter, Dry Drier Standard Rule More Intense Floods and Droughts All Kinds of Water Changes Already Noted More rain/less snow, Earlier Runoff, Higher Water Temps, More Intense Rain

46 American Geophysical Union Fall Meeting San Francisco December every Year 24,000 Earth Scientists Fully Accepted Science Earth is Warming Humans are the Cause Very Risky to Burn Carbon unabated Water Cycle will be Impacted Theory vs Belief

47 Almost every Major Scientific Organization has statement affirming Anthropogenic-caused Warming AND the need to act National Academy of Science All International Academies of Science American Association for the Advancement of Science American Geophysical Union American Meteorological Society The Geological Society of America Many, many others..(but not AAPG)

48 Colorado River Drought Worst Drought in Colorado River Gage Record maf Colorado River Flows 1950s Precipitation Dominated Drought 2000s Temperature Dominated Drought ~ 1/3 of the Decline due to Higher Temperatures % Loss by 2050 Possible due to higher temperatures Colorado River Basin Precipitation Increases in precipitation may counteract losses somewhat inches Increased risk of megadrought in 21 st century reinforces loss potential Colorado River Basin Temperatures F 44 Sources: Udall and Overpeck, 2017; Woodhouse et al., Annual Data Average Linear Trend Loess Smooth