Climate change and snowfed rivers in southwestern United States

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1 Climate change and snowfed rivers in southwestern United States Climatic and hydrologic setting Declining snowpack declining streamflow? Uncertainties in climate impacts assessments David S. Gutzler University of New Mexico UNAM 11 Oct 2018

2 J.W. Powell (1891) Hydrogeography of the Interior Western U.S. Snow-fed rivers High elevation headwaters basins Rivers supply surface water to arid lands downstream snow dominated Upper Rio Grande basin rain dominated 2/19

3 The Upper Rio Grande basin Annual Precipitation Runoff Generation (snow) CO Albuquerque (rain, or not) NM El Paso/Juarez CH TX 3/19 Phillips et al. (2011)

Annual Snow Climatology inches of snowfall 1961-1990 data snow is now decreasing,

4 Annual Snow Climatology inches of snowfall data snow is now decreasing, especially along the snowpack margin days of snow cover 4/19 maps: Colorado State University

5 Reconstructed precipitation variability, northern NM 140% based on tree ring data NM Climate Division 2 80% Taos Pueblo NMOSE (2006), from G. Garfin (U. Arizona) 5/19 ±20% changes on decadal time scales is typical

6 Proxy Rio Grande streamflow: Otowi gage Reconstructed Rio Grande Streamflow at Otowi 11-year running average ±20% based on tree ring data flow (million acre-feet) Otowi gage 6/ year 2000 Huge multidecadal fluctuations in precipitation and streamflow treeflow.org Gutzler (2012)

correlated with winter/ spring precipitation across the

7 Pacific Decadal Oscillation warm phase; AK salmon PNW salmon cold phase; AK salmon PNW salmon wet wet correlated with winter/ spring precipitation across the Southwest dry dry /19 Mantua et al. (1997)

8 Projected Temperature Change A1B scenario * Enhanced polar warming * Continents warm more than oceans IPCC AR4 * US Mountain West is a "hot spot" for warming (already happening) 8/19

9 Projected Change in Precipitation CMIP3 global models, A2 scenario Winter Spring Fall: Strong South-North gradient in Δprecip Much drier across northern Mexico Summer: Weaker trends, but more variable precip and more extreme events Considerable model disagreement 9/19 US NCA3 (2014)

projected decrease in mean winter snowpack especially where temperature is barely cold enough for

10 How much snow can we expect in a warmer climate? CMIP3 CMIP5 Brutel-Vuilmet et al. (2013) Brown and Mote (2009) IPCC Assessment: "Medium Confidence" 10/19 Large projected decrease in mean winter snowpack especially where temperature is barely cold enough for snow Diminished snowpack also melts earlier in the year... hence earlier timing of snowmelt runoff peaks in seasonal hydrographs

11 How much will snow-fed rivers diminish? Projected mid-century change in streamflow Older projections "Middle" (NM) Rio Grande: 3 different CMIP3 projections (A1B) current climate >20% decrease Milly et al. (2005) Hurd & Coonrod (2012) A result of higher temperature? ( increased evapotranspiration) E 11/19 More recently: Bureau of Reclamation West-Wide Assessments US National Climate Assessment

12 T [F] Observed climate variability in NM Temperature Precipitation P [in] T: rising ~7 F/century (~4 C/century) P: huge variability P+T: episodic droughts become much worse snowmelt runoff was lower in the early 21 st Century compared to the 1950s drought 12/19 NOAA divisional data from WRCC

13 Inches Inches Observed Variability in the Upper Rio Grande Basin o Temp ( F) Temperature and Precip CO Division 5 Precip (in) Temperature has increased ~3F since the early 1970s Very small increase in precipitation (natural?) 5 SWE (in) 1 April Snowpack Upper Rio Grande basin Snowpack has decreased ~25% since the early 1970s 13/19 Chavarria & Gutzler (2018) from NOAA and NRCS data

14 Upper Rio Grande Hydrograph Changes * Not much change in total discharge * Shift from June peak to earlier months Chavarria & Gutzler (2018) 14/19

Newer (CMIP5) Projections (Upstream: Rio Grande at

(although snowpack decreases) Runoff: More in Apr

10 Spring Precipitation: decrease Jun 4 1950 2000

with D(precipitation), not DT 1960 2020 2080 15/19

15 Newer (CMIP5) Projections (Upstream: Rio Grande at Del Norte) Apr 20 Winter Precipitation: increase (although snowpack decreases) Runoff: More in Apr Less in Jun Huge Spread May Spring Precipitation: decrease Jun Projected DQ is principally correlated with D(precipitation), not DT /19 Bjarke & Gutzler (2018) using CMIP5/USBoR simulations

16 Apr-Jul Discharge [Mm 3 ] Is climate change already affecting seasonal streamflow forecasts? Q-SWE correlation Upper Rio Grande Residual correlation between Q and Spring P /19 1 Apr Snowpack Apr-Jun precipitation Chavarria & Gutzler (2018)

17 Temperature Projected Climate Changes Precipitation No decline observed in SW US 17/19 US NCA3 (2014)

18 The Big Picture: Science Challenges Snowfed rivers are at long-term risk from climate change But why, and how much flow reduction should we expect? Drought (precipitation deficits) are worsened in a warmer climate This is the message that needs to be reiterated Annual water supply outlooks are losing skill, just when they are more important than ever Trends and variability in Spring precipitation need to be incorporated into outlooks and projections more explicitly A challenge for CMIP6 and AR6 18/19

19 The Big Picture: Policy Challenges for Western Water 21 st Century Climate & Population, 20 th Century Infrastructure, 19 th Century Water Laws and acknowledgment of climate change [Brad Udall, CSU] Uncertainties in hydroclimatic projections (annual, longer term) what is actionable information? what is the value of a 50-year forecast? Depletion of the groundwater buffer as surface water gets scarce Thanks! Students: Shaleene Chavarria Nels Bjarke Sean Leister Nolan Townsend 19/19 Funding:

Precipitation and Streamflow in Mountainous, Middle-Latitude Terrain snow rain snow winter snowpack convenient, low-loss seasonal storage predictable snowmelt runoff large-scale rain (winter, spring,

20 Precipitation and Streamflow in Mountainous, Middle-Latitude Terrain snow rain snow winter snowpack convenient, low-loss seasonal storage predictable snowmelt runoff large-scale rain (winter, spring, autumn) falls over a wide area maybe some seasonal predictability gage storage For surface water resource management, not all precipitation is created equal convective rain (summer thunderstorms) minimal predictability, spotty high E: low recharge, flashy runoff 14/25

Newer Projections (Downstream: Rio Grande at San Marcial) Observed annual flow HadGEM2 (CMIP5) Average of all simulations Modest long-term decrease Very large spread between

21 Newer Projections (Downstream: Rio Grande at San Marcial) Observed annual flow HadGEM2 (CMIP5) Average of all simulations Modest long-term decrease Very large spread between models Inadequate decadal variability? Hints of failure to simulate observed changes in snowpackstreamflow relationship Townsend (2018) using CMIP5/USBoR simulations 16/25

22 Seasonal Streamflow Forecasts in a Changing Climate Upper San Juan SNOTEL Basin SWE (% Average) 27 Feb 2018 Feb 27 Oct Dec Feb Apr Jun A horrendously dry snow accumulation season across the Southwest 18/25

23 T [F] Is climate change already affecting seasonal streamflow forecasts? Trend in NRCS Forecast Skill Upper Pecos River Why does the skill of seasonal water supply outlooks on the upper Pecos River seem to get worse starting in the 1970s? start of 20-year validation window Pagano et al. (2004) 20/25

24 NRCS Feb 1 Water Supply Outlooks for 2018 Spring/Summer Forecast for: Rio Grande Del Norte (headwaters): 50% average Otowi (northern NM): 21% average San Marcial (southern NM): ~0 Upper CO Upper San Juan R: 45% of avg Upper Pecos basin: 26% of avg Upper Gila basin in NM: 24% of avg Lower CO RG ARK These forecasts have tended to overestimate flows in recent years 19/25

25 22/25 What happened to the snow in 2018?

26 New Mexico reservoir volumes 31 Jul 2018 Elephant Butte Reservoir storage EB Albuquerque Elephant Butte Reservoir has been drained this year El Paso 23/25 90 kaf or 4.6% full as of Aug 26 ~1 kaf/day depletion rate waterdatafortexas.org CLIMAS / U Arizona

27 Return flow to the Rio Grande... from treated wastewater head-waters from the ABQ Wastewater Treatment Plant, just south (downriver) from the city abcwua.org

28 Middle Rio Grande Water Budget Projected 21st Century Changes Major Inflows Flow from headwaters Flow from tributaries Input from groundwater Major Depletions Evaporation Riparian transpiration Agriculture Urban consumption Groundwater Recharge Depletions Inflows Ch 3 - Fig 4

29 Apr-Sep Flow [KAF] NRCS Rio Grande Streamflow Outlooks for 2018 Del Norte Colorado gage J F M A M J WY 2018: median forecast = 255 Kaf (50% median) 2017 obs (107%) 30-year median 20/27 NRCS Water Supply Outlooks

The Rio Grande Compact: NM's downstream delivery obligation Otowi Elephant Butte NM delivery obligation to TX (below EB Reservoir) Available for depletion above EB Dam (including reservoir

30 The Rio Grande Compact: NM's downstream delivery obligation Otowi Elephant Butte NM delivery obligation to TX (below EB Reservoir) Available for depletion above EB Dam (including reservoir evaporation) median Index Supply flow ( ): 816 kaf NM and TX share shortages in low-flow years (flow < 1000 Kaf)... which recently has been every year! Most recent median flow year: 2010 A cyclic drought, or beginning of a trend?

31 US Seasonal Climate Outlooks (issued 16 Aug 2018) Temperature Precipitation 4.5 month outlooks, for Jan-Mar

32 23/27 Water Crisis on the Rio Grande in 2019

33 The Longer-Term Outlook We do not expect this year's extreme dryness to become a new "normal" condition. but All credible climate change projections call for a trend toward warmer, dryer conditions this century warmer temperatures very likely (count on it) some average reduction in precipitation is probable At least we can see it coming and plan accordingly collaborative USDA project in the works Thanks! Students: Shaleene Chavarria Nels Bjarke Shawn Leister Nolan Townsend 20/21 Funding:

34 Apr-Jul Discharge [Mm 3 ] Snowpack-streamflow regressions Based on 1 Apr SWE In later epoch: Better linear fit (Q depends more directly on SWE) Shallower regression slope (reduced sensitivity of Q to SWE) Challenge: current climate models do not reproduce these changes 11/21 Chavarria & Gutzler (2017)

Equatorial cold tongue, most prominent in Pacific, and not present at

35 Global SST Jan-Apr 2018 * General poleward decrease of surface temperature * Upwelling zones along continental west coasts * Equatorial cold tongue, most prominent in Pacific, and not present at all in Indian Ocean * Cold anomalies (blue) across eastern equatorial Pacific La Niña

36 Effect of El Niño on trough/ridge pattern across the North Pacific and North America This wavetrain in the middle/upper troposphere is known as the Pacific/North American (PNA) pattern The wavetrain is thought to be an example of a Rossby wave forced by the anomalous equatorial ocean temperature a "teleconnection" pattern jet stream deflected southward Fig

37 So What To Do? Protect and conserve your water (we're getting better at this!) Treat your groundwater supply as a truly precious buffer against surface water shortages Future generations would appreciate it if we took climate change seriously thanks! 21/21

38 Precipitation Climatology (NM) Red River Otowi Ch 4 - Fig 2 Socorro Ft Bayard Elephant Butte Dam Roswell Ch 4 - Fig 1

39 Status of Drought: August 2018 Drought = "Not enough water" (anomalously so) At present: USDM suggests Exceptional drought to our north Improvement to drought in middle RG Valley

40 mid-may mid-aug 2018 Global Ocean Temperature * General poleward decrease of surface temperature * Upwelling zones along continental west coasts * Equatorial cold tongue, less prominent in Pacific, in NH late spring / summer * La Niña has disappeared El Niño projected to intensify NOAA Earth Systems Research Laboratory

41 Temperature Climatology T max July T min January

42 Seasonal Outlook Suite [issued 8/16/2018; updated monthly by NOAA] OND-DJF (2018) JFM-MAM (2019) AMJ-JJA JAS-SON Temperature Precipitation

Observed SST anomalies May-Aug ENSO outlook late summer 2018 Nino3.4: 5ºN-5ºS, 170-120ºW SST anomaly map:.

43 Observed SST anomalies May-Aug ENSO outlook late summer 2018 Nino3.4: 5ºN-5ºS, ºW SST anomaly map:... mostly global warming, with some positive anomalies in W tropical Pacific issued 8/06/2018 NOAA s Consolidated Forecast... for Nino3.4 averaging region... developed from an ensemble of different models (dynamical, statistical)

44 Ch 3 - Fig 2 The Rio Grande x A snowfed river with highly variable flow Rio Grande at Otowi Ch 3 - Fig 3 snowmelt runoff peak (May) Monthly Average Flow Otowi gage Annual Time Series

Drought and Future Water for Southern New Mexico

Drought and Future Water for Southern New Mexico David S. Gutzler University of New Mexico gutzler@unm.edu * The big drought of 2018 * Longer term challenges for water supply * Forecasting streamflow Elephant