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 Butte Reservoir Lush & Lean March 1, 2018
USGS Monitoring Well Network Water for Las Cruces and the Mesilla Valley City of Las Cruces: Supplied by groundwater Agriculture: Supplied by groundwater and Rio Grande surface water (released from storage in Elephant Butte Reservoir) à Rio Grande is mostly snow-fed Ultimately, surface water and groundwater are connected 2/21
New Mexico reservoir volumes Elephant Butte Reservoir storage 31 Jan 2018 Recovery above 400 Kaf since mid-dec (487 kaf or 24.7% full as of Feb 26) waterdatafortexas.org CLIMAS / U Arizona 3/21
Status of Drought: February 2018 The US Drought Monitor is largely based on precipitation At present: DM suggests severe drought across the northern 2/3 of NM and extreme drought in the northern mountains 4/21
Snowless Winter of 2017-18 across the Southwest Basin SWE (% Average) 27 Feb 2018 Upper San Juan SNOTEL Feb 27 Oct Dec Feb Apr Jun A horrendously dry snow accumulation season across the Southwest 5/21
Current U.S. seasonal outlook: for Mar-May 2018 Temperature Precipitation issued 15 February 2018 6/21 Warmer and drier than average across southern NM
NOAA Earth Systems Research Lab La Niña Isn't Helping Precipitation at Las Cruces During La Niña Winter Months Current Global Ocean Temperature Anomaly Map Univ of Arizona / CLIMAS
Pacific Decadal Oscillation warm phase; AK salmon PNW salmon cold phase; AK salmon PNW salmon wet wet à correlated with "cold season" precipitation across the Southwest dry dry 1910 1930 1950 1970 1990 2010 8/21 Mantua et al. (1997)
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 San Juan R: 45% of avg Upper Pecos basin: 26% of avg Upper Gila basin in NM: 24% of avg These forecasts have tended to overestimate flows in recent years!! 9/21 We are here
NRCS Rio Grande Streamflow Outlooks for 2018 Del Norte Colorado gage Apr-Sep Flow [KAF] 900 800 700 600 500 400 300 200 100 0 2018 2017 1 2 3 4 5 6 J F M A M J 2017 obs (107%) 30-year median WY 2018: median forecast = 255 Kaf (50% avg) 10/21 NRCS Water Supply Outlooks
Snowpack-streamflow regressions Based on 1 Apr SWE 1958-1986 In later epoch: Apr-Jul Discharge [Mm 3 ] 1987-2015 Better linear fit (Q depends more directly on SWE) Shallower regression slope (reduced sensitivity of Q to SWE) 11/21 Chavarria & Gutzler (2018)
Reconstructed precipitation change, northern NM 140% based on tree ring data NM Climate Division 2 80% Taos Pueblo 1000 1500 2000 NMOSE (2006), from G. Garfin (U. Arizona) 12/21 ±20% changes on decadal time scales is typical
Proxy Rio Grande streamflow: Otowi gage 2.2 2.0 Reconstructed Rio Grande Streamflow at Otowi 11-year running average ±20% based on tree ring data flow (million acre-feet) 1.8 1.6 1.4 Otowi gage 1.2 13/21 1500 1600 1700 1800 1900 2000 year Huge multidecadal fluctuations in precipitation and streamflow treeflow.org Gutzler (2012)
Decreasing snowpack Peak Snowpack Upper Rio Grande Basin 21 st Century Projected Snowpack Chavarria & Gutzler (2018) 14/21 1958 2015 25% observed decrease since late 1950s Large projected decrease in mean winter snowpack especially where temperature is barely cold enough for snow Brown and Mote (2009) Diminished snowpack also melts earlier in the year... hence earlier timing of snowmelt runoff peaks in seasonal hydrographs
Observed climate variability in NM T [F] Temperature Precipitation T: rising ~7 F/century (~4 C/century) P: huge variability P+T: episodic droughts become much worse P [in] 1950s drought 15/21 NOAA divisional data from WRCC
Projected temperature change in the Southwest Temperature Projections A1B scenario * Enhanced polar warming * Continents warm more than oceans IPCC AR4 * US Mountain West is a "hot spot" for warming (already happening) 16/21
Projected Change in Precipitation by 2080-2099 CMIP3 global models, A2 scenario Winter: Strong South-North gradient in Δprecip Much drier across northern Mexico Summer: Weak general tendency toward less precip, but more variable & extreme events Considerable model disagreement 17/21 USGCRP (2009)
Projected Middle Rio Grande Streamflow current climate - - - 2020-2050 - - - 2070-2100 3 different model projections (A1B-forced) Hurd and Coonrod (2012) Snowpack currently feeds a late Spring flood pulse on the upper Rio Grande and its tributaries 18/21 In the future (warmer) climate: Earlier & weaker snow-fed flood pulse Reduced total streamflow volume, especially in late spring/early summer 2030s: 4-14% reduction 2080s: 8-29% reduction
Short term Outlook: Severe Hydrologic Drought The extreme lack of precipitation this Fall and Winter is probably a persistent weather event Some degree of snowpack recovery could happen, but it is very unlikely we'll see close to average snowpack or streamflow this year and EB Res level is already low At least we can see it coming and plan accordingly Yikes, is there any good news? La Niña ocean anomalies (associated with warm, dry winters in New Mexico) tend to decay within a year Summer monsoon rains won't necessarily fail 19/21
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 20/21
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 Las Cruces is not Cape Town Future generations would appreciate it if we took climate change seriously thanks! 21/21