The Drying Climate in the American West...• Response of Colorado River runoff to dust radiative...
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Brad Udall Senior Scientist/Scholar Colorado State University [email protected] The Drying Climate in the American West 63 rd Annual New Mexico Water Conference October 17, 2018 Las Cruces, NM Lake Creek, Colorado September 8, 2018 https://bit.ly/2NKGnsD
Transcript of The Drying Climate in the American West...• Response of Colorado River runoff to dust radiative...
Brad Udall Senior Scientist/ScholarColorado State [email protected]
The Drying Climate in the American West
63rd Annual New Mexico Water ConferenceOctober 17, 2018Las Cruces, NM
Lake Creek, ColoradoSeptember 8, 2018
https://bit.ly/2NKGnsD
Water Year 2018 Temperature
Water Year 2018 Precipitation
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
The 2000-18 Millennium Drought is very, very different from previous droughts in the historic record…
Represents 6 maf loss over 18 years relative to worst 20th century drought
Millennium Drought 2000—2018
• 2000-2017 is the worst drought in the gaged record
• ~ 20%/yr decline
• Long-term trend, too
Udall and Overpeck, WRR, 2017
Millennium Drought 2000—2018
• 2000-2017 is the worst drought in the gaged record
• ~ 20%/yr decline
• Long-term trend, too
• Lakes Powell and Mead have lost 50% of their volume
Udall and Overpeck, WRR, 2017
Millennium Drought 2000—2018
• Precipitation declines only partially explain
• ~ 2/3 of the loss
Udall and Overpeck, WRR, 2017
Millennium Drought 2000—2018
• Precipitation declines only partially explain
• ~ 2/3 of the loss
• Temperature increases explain the remainder
• ~ 1/3 of the loss• Why?
• More Evaporation• Thirstier
Atmosphere
• Temperature-Induced Losses
• Now = ~6%• 2050 = ~20%• 2100 = ~35%
Udall and Overpeck, WRR, 2017
Udall and Overpeck, WRR, 2017
• Temperature can be a major flow driver• Since 1988 flows have been less than expected given winter precipitation• Warm temperatures exacerbated modest precipitation deficits in the
Millennium Drought
Model-based Study using Historical Data– Long-term Trend Analysis
(-16.5% Decline)– Temperature De-trend Model
Experiment– 1950s vs 2000s Drought Analysis– 2017 Forecast Analysis
• Findings– ~50% of Decline due to Higher
Temperatures– ~50% of Decline due to Changing
Precipitation Patterns4 Key Basins (Green + Blue) produce ~55% of all runoff
Denver Water Forecast Inflow vs Runoff 2018
• Colorado River snowpack peaked at 107% of normal
• South Platte River snowpack peaked at 85% of normal
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%
April through July Natural Streamflow Percent of Average
Source: Denver Water
-22%
Denver Water Forecast Inflow vs Runoff 2018
• Colorado River snowpack peaked at 107% of normal
• South Platte River snowpack peaked at 85% of normal
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%
April through July Natural Streamflow Percent of Average
Source: Denver Water
-22%-10%-28%-10%
New Normal?
Dave Pierce, Scripps
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…
Aridification – not a drought
• Declining Snowpack and earlier runoff
• Higher Temperatures• Drying Soil• Thirsty Atmosphere• Moving storm tracks• Shorter Winter/Longer Fall• Greening ?• Megadrought?
Seager et al., 2018
Aridity Index (P/PET) Changes
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
Changing Precipitation Patterns: Dry South, Less Dry North
Changes in Soil Moisture in 2100
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)
Cook Science
In both Central Plains and Southwest, Multi-decadal Drought Risk* exceeds 80% in 21st
Century
* Defined as Drought lasting 35 or more years
Percent Chance of Multi-DecadalDrought Risk,Southwest US
P = +10%
P = +20%
P = +10%
P = +20%
Risk = 70% w/ +10%
Risk = 35% w/ +20%
Other Supporting 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
Seager et al., 2015
Mote et al., 2018
Snow Water Equivalent Trends
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
Increasing Heat Content Everywhere
90% into the ocean
FOLU = Forestry, Other Land Use
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
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”
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)
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
Climate Change a combination of …
1. For-Sure Temperature Rise -> Flow Losses
2. Not-Sure Precipitation Change -> Flow Gains or Losses
Colorado River Future Flow Losses
In the future, plants move up slope, increasing evapotranspiration.
By 2100 ET increases by 28% and Kings River flows decline by 26%.
Evapotranspiration Increases in Natural Systems
Now Future
Colorado River Drought 2000-2014
Sources: Udall and Overpeck, 2017; Woodhouse et al., 2016
• 2000-2014 Worst Drought in Colorado River Gage Record
• ~ 1/3 of the Decline due to Higher Temperatures
• 20% Loss by 2050 Possible due to higher temperatures
• Increases in precipitation may counteract losses somewhat
• Increased risk of megadrought in 21st century reinforces loss potential
