21st Century Climate Change In SW New Mexico: What s in Store for the Gila? David S. Gutzler University of New Mexico

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1 21st Century Climate Change In SW New Mexico: What s in Store for the Gila? David S. Gutzler University of New Mexico gutzler@unm.edu Silver City, NM June 5, 2008

2 Global Warming in the 20th/Early 21st Centuries Warmest years: 1998 and warmest years have all occurred since 1995 Subcentury trends : warming before 1940 cooling rapid warming since 70s over the past century: about 0.7 C ± 0.2 C

3 Northern Hemisphere temperature for the past two millennia (mostly tree ring-based) Warming in the Northern Hemisphere began in the 17th Century... but 20th Century warming is large and rapid compared to any period in the past 2000 years

4 Global Warming in the 20th/Early 21st Centuries

5 New Mexico Climate Divisions The global average temperature is of little concern to most people and policymakers. 4 6 But global climate models simulate very large scale processes. 5 8 These climate division averages get us somewhat closer to society-relevant projections. 7

6 45 NM Temperature DJF CD4 Temperature, NM CD T DJF cd4 obs T DJF cd4 A1B T DJF cd NM Temperature Annual (WY) CD4 Temperature (F) T WY cd4 obs T WY cd4 A1B T WY cd year Temperature (F) Temperature (F) T JJA cd4 obs T JJA cd4 A1B T JJA cd4 11 NM Temperature JJA CD year year observed values values calculated from the trend of the A1B ensemble scenario, with observed 20th Century interannual variability superimposed 11-yr running average

7 Precipitation, NM CD4 4 Precipitation (in) NM Precipitation DJF CD4 P DJF cd4 obs P DJF cd4 A1B P DJF cd4 11 Precipitation (in) NM Precipitation Annual (WY) CD4 P WY cd4 obs P WY cd4 A1B P WY cd year 10 Precipitation (in) NM precipitation JJA CD4 P JJA cd4 obs P JJA cd4 A1B P JJA cd year year observed values values calculated from the trend of the A1B ensemble scenario, with observed 20th Century interannual variability superimposed 11-yr running average

8 Proxy precipitation history of north-central New Mexico Fig II-4 based on tree ring data NM Div 2 G. Garfin (U. Arizona) The most prominent features in this data record are found in other SW climate records too

9 Late 20 th Century temperature trends in southern New Mexico HDD daily = max{0, 65 F-(T max +T min )/2} Change from 1950s to the end of the 20th Century exceeds 15% for both HDD and CDD... this trend is already affecting your utility rates CDD daily = max{0, (T max +T min )/2-65 F} NCDC data

10 Scenarios for 21st Century climate changes Based on four 21st Century CO 2 emissions scenarios: A2: No emissions policy ( business as usual ) A1B: Less ambitious policy: 690 ppmv in 2100 B1: More ambitious policy: 550 ppmv in 2100 Current commitment : CO 2 remains at 2000 concentration... many other scenarios have been tested Meehl et al. (2005)

11 Uncertainty in sea level rise: How rapidly will ice sheets melt? Rahmstorf (2007) IPCC models exclude rapid dynamical changes in ice flow. This model includes such effects; sea level rise occurs about 3x faster than IPCC estimates

12 Prediction: Temperature in the Southwest will continue to increase - at a faster rate Temperature trends across North America in the late 21st Cent. IPCC AR4 18-model average A1B scenario The Southwest is a hot spot for temperature change as we already observe Temperature trends New Mexico statewide in the 21st Century summer NM OSE (2006) winter

13 Projected precipitation changes in late 21st Century More precipitation near equator and in mid-latitude storm tracks Less precipitation in subtropical latitudes... Essentially an expansion of the Hadley Circulation IPCC (2007)

14 Projected hydrologic changes in the late 21st Century New Mexico American Southwest Seager et al. (2007) Global climate models predict a transition into nearly perpetual drought by the second half of the 21st Century NM OSE (2006) / Gutzler (2007)

15 45 NM Temperature DJF CD4 Temperature, NM CD T DJF cd4 obs T DJF cd4 A1B T DJF cd NM Temperature Annual (WY) CD4 Temperature (F) T WY cd4 obs T WY cd4 A1B T WY cd year Temperature (F) Temperature (F) T JJA cd4 obs T JJA cd4 A1B T JJA cd4 11 NM Temperature JJA CD year year observed values values calculated from the trend of the A1B ensemble scenario, with observed 20th Century interannual variability superimposed 11-yr running average

16 Precipitation, NM CD4 4 Precipitation (in) NM Precipitation DJF CD4 P DJF cd4 obs P DJF cd4 A1B P DJF cd4 11 Precipitation (in) NM Precipitation Annual (WY) CD4 P WY cd4 obs P WY cd4 A1B P WY cd year 10 Precipitation (in) NM precipitation JJA CD4 P JJA cd4 obs P JJA cd4 A1B P JJA cd year year observed values values calculated from the trend of the A1B ensemble scenario, with observed 20th Century interannual variability superimposed 11-yr running average

17 Projected change in western snowpack IPCC AR4 % change in March snowdepth by mid-21st Century A2 scenario Decreases throughout western mountains are seen in climate model simulations US Global Change Research Program The decreases are due principally to temperature change (more rain, less snow) In NM: snowpack disappears south of Santa Fe

18 Projected change in snowmelt runoff timing much earlier peak runoff date, driven by warmer temperature (less snow, warmer springtime temperatures) Stewart et al. (2004)

19 Prediction: Soil moisture will decrease ET over land will decrease Soil Moisture March-April-May average Evapotranspiration June-July-August average... BUT: Under these conditions evaporation over water surfaces (not resolved in this model) would dramatically increase Difference ( ) - ( ) N. Diffenbaugh (Purdue U.)

20 Effects of projected climate change on Rio Grande basin streamflows Earlier snowmelt flood pulses and much reduced total streamflow volume Hurd and Coonrod (2007)

21 Inflows San Juan-Chama Inflow Tributary Inflow (gauged) Municipal Waste Water Albuquerque Storm Drain Inflow San Acacia Gauge Otowi Gauge 1419 ( ) Middle Rio Grande 74 (37-111) 123 (86-160) Discharge from Aquifer to Surface Recharge to Aquifer 123 (99-222) Open Water Evaporation Irrigated Agriculture & Valley-Floor Turf Shallow Aquifer 167 (93-241) Riparian ET, Irrigated Agriculture, & Open Water Evaporation Estimated water budget Middle Rio Grande (10 6 m 3 /yr)? Depletions Riparian Evapotranspiration (ET) In a warmer climate: Inflows decrease and depletions increase Dahm et al. (2002) 173 (49-281) To Downstream ( ) Users Elephant Butte Reservoir Evaporation What about the Gila River?... I would expect a more dramatic snowpack-forced decrease in flows, and much warmer temp.

22 Rio Grande What about flows in the Gila River? Monthly Average Streamflow Gila River near RedRock NM streamflow (cfs) month * Snowpack could be nearly eliminated * Current double peak hydrograph would be flattened in winter and greatly reduced in spring... reduced annual flow * What about the summer monsoon peak? BUT: This area has not been modeled thoroughly, and I don t see evidence of long term trends in current data (LOTS of variability, especially in recent years)

23 What about the Gila (part II)? a tale of warmer water temperature starring the Gila Trout, and scripted by Tom Kennedy (UNM Biology PhD student) Oncorhynchus Gilae current Gila Trout habitat

24 Resolution of Global Climate Models: A challenge for local/regional analysis of climate change Hurd and Coonrod (2007) Here is one grid cell from a 1990s global climate model Newer models are smaller but still are about 100 km (50 miles or so) on a side... so we use a smaller scale regional model (about 20 km on a side), and then statistically downscale those results to fit the scale of Gila Trout watersheds

25 Climate change at high elevation in the Gila Country Average warming in summer in this simulation is about 2 C (3-4 F) But this average increase implies many more hot days ( hot = above limit that Gila Trout can tolerate) Summer precipitation also decreases in this scenario Total length of streams suitable for Gila Trout habitat decreases by about 70% Indirect effects of warming (like more frequent and intense wildfires) would exacerbate this effect Kennedy et al. (2008)

26 USDA Plant Hardiness Zones New Mexico features a huge range of these plant zones! Each zone covers a range of 5 F US Dept of Agriculture By mid 21 st Century: change 1 zone warmer? By end 21 st Century: change 2 zones warmer?

27 Principal Effects of Projected Climate Change on southwestern New Mexico Temperature increases, now clearly observed, are likely to continue at an accelerated rate as greenhouse gas forcing slowly overwhelms other known climate forcings. Rises in temperature and sea level are, by far, the most robust climate change predictions we can make... but the rate of changes to expect is (and will remain) uncertain. Warmer temperatures will lead to reduced snowpack, less spring runoff, lower streamflows, more evaporation from reservoirs, and drier soil conditions... the Gila may cease to be a snow-fed river. The impacts of episodic droughts would be more severe in a warmer climate, regardless of long-term trends in precipitation... we expect the climate to become more variable. Thanks to UGWA for inviting me here, and thanks for your interest!