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The Changing Gila River: Past, Present and Future€¦ · NM4 Nov-Apr Precipitation plotted against...
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The Changing Gila River: Past, Present and Future David S. Gutzler University of New Mexico [email protected] How is the hydrograph on the upper Gila projected to change as climate warms up? Snowmelt runoff? Summer low flows? We'll use observations, coupled dynamical models, and simple statistical models Three ISC technical reports (2013, 2015, 2016) New Mexico Water Conference October 6, 2016 AZ NM Catron Co Grant Co Sierra Co Gila gage
Transcript of The Changing Gila River: Past, Present and Future€¦ · NM4 Nov-Apr Precipitation plotted against...
The Changing Gila River: Past, Present and Future David S. Gutzler
University of New Mexico [email protected]
à How is the hydrograph on the upper Gila projected to change as climate warms up?
à Snowmelt runoff? Summer low flows?
à We'll use observations, coupled dynamical models, and simple statistical models
à Three ISC technical reports (2013, 2015, 2016)
New Mexico Water Conference October 6, 2016
AZ NM
Catron Co
Grant Co
Sierra Co
Gila gage
Average annual hydrograph: Upper Gila River
Horner and Dahm (2014) TNC Flow Needs Assessment
Feb - May Jun - Jul Aug Sep - Jan
Note! Mean >> Median flow most of the year Hydrograph ≠ Seasonal Precipitation
Mean
Median
Reconstructed Past Flows
Meko et al. (2010) treeflow.info
(Solomon gage)
Highly variable flow across decades (±30%) Flow largely correlated with precipitation
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
WGI AR4 (2007)
US Mountain West is a "hot spot" for warming (already happening)
Temperature
Precipitation
Winter Summer
The big projected change: Decreasing snowpack
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
Brown and Mote (2009)
NARCCAP Gila Basin: 21st Century change
Δ Median Snow Water
Oct Jan Apr Jul
0
Jon Lewis, UNM
Dynamical Projection Gila gage (BoR, 2011) median of
all 39 simulations
Largest decreases in Spring runoff season Little projected change in mid-winter months
or in summer months
1950 2000 2050 2100
1950 2000 2050 2100
8% reduction Dec-Jun (2021-2050) – (1951-2012)
Projected climate change (runoff season)
Climate models project continued, significant increase in temperature in 21st Century ... and a relatively modest decrease in P (modest relative to interannual/ decadal variability)
1950 2000 2050 2100
1950 2000 2050 2100
4
CMIP3 A1B
Statistical Projection: Gila gage, runoff season
Observed Temperature and Precipitation (1951-2012)
Regressed onto Observed Gila flow (1951-2012)
NM4 Jan-Apr Temperature plotted against Dec-Jun flow
NM4 Nov-Apr Precipitation plotted against Dec-Jun flow
1950 2000 2050 2100
1950 2000 2050 2100
Obs-based regression applied to projected Temp and Precip, to generate projected Gila flow
1950 2000 2050 2090
7.4% reduction Dec-Jun (2021-2050) – (1951-2012)
8% reduction Dec-Jun (2021-2050) – (1951-2012)
Dynamical projection average:
2. Future of Low Flows in the upper Gila basin
Feb - May Jun - Jul Aug Sep - Jan
Low Flow Season Hypothesis: Monthly Q = f(Qprev, Pconcurrent)
June streamflow: 39 simulations
878 max 607
June: Decreasing flows across the distribution
95% 75%
25% 5%
50%
1951- 2001- 2000 2050
1950 2000 2050
June
str
eam
flow
[cf
s]
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
0
50
100
150
200
250
0 100 200 300 400 500 600 700 800
(a) Q May vs June
June
ave
rage
flow
[cf
s]
May average flow [cfs]
0
50
100
150
200
250
0 50 100 150 200 250
(b) Q June vs July
July
ave
rage
flow
[cf
s]
June average flow [cfs]
r = 0.92 r = 0.24
0
50
100
150
200
250
0 1 2 3 4 5
(b) Q vs P July
July
ave
rage
flow
[cf
s]
July precipitation [in]
0
50
100
150
200
250
0 0.5 1 1.5 2 2.5
(a) Q vs P June
June
ave
rage
flow
[cf
s]
June precipitation [in]
r = 0.13 r = 0.60
Qprev
important for June flow Low Flow Season Hypothesis: Monthly Q = f(Qprev, Pconcurrent)
Pconcurrent important for July flow
June July
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
