The Changing Gila River: Past, Present and Future David S. Gutzler University of New Mexico gutzler@unm.edu à How is the hydrograph on the upper Gila projected to change as climate warms up? Catron Co AZ à Snowmelt runoff? Summer low flows? NM Sierra Co à We'll use observations, coupled dynamical models, and simple statistical models Grant Co Gila gage à Three ISC technical reports (2013, 2015, 2016) New Mexico Water Conference October 6, 2016
Average annual hydrograph: Upper Gila River Feb - May Jun - Jul Aug Sep - Jan Mean Median Note! Mean >> Median flow most of the year Hydrograph Seasonal Precipitation Horner and Dahm (2014) TNC Flow Needs Assessment
Reconstructed Past Flows (Solomon gage) Highly variable flow across decades (±30%) Flow largely correlated with precipitation Meko et al. (2010) treeflow.info
Observed Climate Variability and Change in NM warming trend lots of variability in precipitation NM Universities Task Force on Water Supply Vulnerabilities (2015)
Projected climate change in the 21st Century Winter Summer Temperature Precipitation US Mountain West is a "hot spot" for warming (already happening) WGI AR4 (2007)
The big projected change: Decreasing snowpack NARCCAP Gila Basin: 21 st Century change 0 Δ Median Snow Water Jon Lewis, UNM Oct Jan Apr Jul Brown and Mote (2009) 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
median of all 39 simulations Dynamical Projection Gila gage (BoR, 2011) 1950 2000 2050 2100 Largest decreases in Spring runoff season Little projected change in mid-winter months or in summer months 1950 2000 2050 2100 8% reduction Dec-Jun (2021-2050) (1951-2012)
CMIP3 A1B Projected climate change (runoff season) 1950 2000 2050 2100 Climate models project continued, significant increase in temperature in 21st Century... and a relatively modest decrease in P (modest relative to interannual/ decadal variability) 4 1950 2000 2050 2100
Statistical Projection: Gila gage, runoff season NM4 Jan-Apr Temperature plotted against Dec-Jun flow 1950 2000 2050 2100 Observed Temperature and Precipitation (1951-2012) Regressed onto Observed Gila flow (1951-2012) 1950 2000 2050 2090 Obs-based regression applied to projected Temp and Precip, to generate projected Gila flow 7.4% reduction Dec-Jun (2021-2050) (1951-2012) 1950 2000 2050 2100 NM4 Nov-Apr Precipitation plotted against Dec-Jun flow Dynamical projection average: 8% reduction Dec-Jun (2021-2050) (1951-2012)
2. Future of Low Flows in the upper Gila basin Feb - May Jun - Jul Aug Sep - Jan Low Flow Season Hypothesis: Monthly Q = f(q prev, P concurrent )
June streamflow: 39 simulations 878 max 607 June streamflow [cfs] 50% 95% 75% 25% 5% 1950 2000 2050 1951-2001- 2000 2050 June: Decreasing flows across the distribution
July streamflow: 39 simulations 780 max 1279 July: Little change in average or low flows; highest flows increase
Predictors of Observed Low-Flow Monthly Streamflow 250 June (a) Q May vs June 250 July (b) Q June vs July 200 200 Q prev important for June flow June average flow [cfs] 150 100 July average flow [cfs] 150 100 Low Flow Season Hypothesis: Monthly Q = f(q prev, P concurrent ) 50 0 0 100 200 300 400 500 600 700 800 0 0 50 100 150 200 250 May average flow [cfs] June average flow [cfs] 250 250 50 r = 0.92 r = 0.24 (a) Q vs P June (b) Q vs P July P concurrent important for July flow June average flow [cfs] 200 150 100 r = 0.13 r = 0.60 July average flow [cfs] 200 150 100 50 50 0 0 0.5 1 1.5 2 2.5 June precipitation [in] 0 0 1 2 3 4 5 July precipitation [in]
Conclusions: Climate Change & the Upper Gila River 1) Big projected temperature change (continuation of observed trend) 2) ~5-10% projected decrease in upper Gila River snowmelt runoff (2021-2050) due to climate change... relative to ~30% decadal variability due to natural precip fluctuations 3) Lowest flows and principal low-flow season changes projected in June Uncertain mean change in July, with higher variability 4) We can derive these results using multiple, complementary techniques à combining observations, dynamical and statistical models 5) What about other rivers in NM?. Shaleene Chavarria's poster re URG Thanks! UNM students: John Carilli, Jon Lewis, Justin O'Shea NM Interstate Stream Commission US Bureau of Reclamation, The Nature Conservancy