The Impacts of Climate Change on Western Water Resources

1
The Impacts of Climate Change on Western Water
Resources
David S. Gutzler University of New
Mexico gutzler_at_unm.edu
IPCC AR4 (2007)

• Climate change is already happening
• Well almost certainly get much warmer
• causing large projected effects on snowpack
  (?) stream flow (?) reservoir evaporation
  (?) drought severity (?) climate
  variability (?) municipal water demand (?)

Global mean temperature
LWV Climate Change in New Mexico August 21, 2009
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Global Warming in the 20th/Early 21st Centuries
Warmest years 1998 and 2005 10 warmest years
have all occurred since 1997

• Subcentury trends
• warming before 1940
• cooling 1940-1975
• rapid warming since 70s

over the past century about 0.7?C ? 0.2?C
3
Temperature, NM CD5
winter
annual
summer
4
Seasonal Temperature Prediction
issued 21 May 2009, for May-June-July 2010
Southwest Warmer than normal
NOAA Climate Prediction Center
5
Longer growing season (already observed here)
SW states
all 48 states
Groisman and Knight (2008)
Duration of the warm season (avg daily T gt 5C)
6
Observed Heating Degree-Day trends in Albuquerque
Change in HDD over the past several decades
exceeds 15
NCDC data
7
Temperature, NM CD5
winter
annual
summer
8
Greenhouse-gas forced climate change
Meehl et al. (2005)
data
Projections based on four 21st Century CO2
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
CO2 remains at 2000 concentration ... many other
scenarios have been tested
I will use A1B
9
Temperature, NM CD5
winter
annual
5.8 F/century
6.9 F/century
ABQ ? Juárez
summer
7.4 F/century
10
Precipitation, NM CD5
winter
annual
summer
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Increasing variability of climate
Probability of exceptionally long dry spells
during the warm season (Southwest US)
Frequency of exceptionally heavy precipitation
events (all 48 states)
Groisman and Knight (2008)
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More intense precipitation in a warmer climate
A2 A1B B1
Sun et al. (2007)
Compared to simulations of current climate,
global models generate fewer, but more intense,
precipitation events as the climate warms up
13
Prediction Soil moisture will decrease
ET over land will decrease
Soil Moisture March-April-May average
Evapotranspiration June-July-August average
Difference (2071-2095) - (1961-1985)
N. Diffenbaugh (Purdue U.)
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Projected 21st Century Drought Severity
Average Palmer Drought Severity Index (20th
Century baseline)
The PDSI reflects a changing water budget
(Precipitation - Evaporation) associated with the
scenario shown earlier By the late 21st Century,
"severe drought" (as defined in the 20th Century)
becomes the norm across New Mexico This is
principally due to higher evaporation, caused by
warmer temperatures
observed
future
Robbins (2009)
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The projected Drying of the West(extreme
negative PDSI values)
Robbins (2009)
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Projected decrease in snowpack
Brown and Mote (2009)
Large projected decrease in mean winter
snowpack especially where temperature is barely
cold enough for snow
17
Projected Streamflow Changes
mid-21st Century projection, relative to 20th
Century baseline
Milly et al. (2005)
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Streamflows on mainstem rivers are projected to
decrease significantly
Christensen et al. (2004)
Projected changes in average total Colorado River
Basin reservoir storage ? The Colorado River
Compact becomes unenforceable
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Present and Predicted Rio Grande Streamflow
Current climate Snowpack feeds late spring
flood pulses on the Rio Grande and its
tributaries
Future climate Earlier and weaker snow-fed
flood pulse Greatly reduced total streamflow
volume, especially in late spring/ early summer
Hurd Coonrod (2007)
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Estimated water budgetMiddle Rio Grande (106
m3/yr)
Otowi Gauge 1419 (370-2714)
Inflows
68
San Juan-Chama Inflow
74 (37-111)
Open Water Evaporation
Tributary Inflow (gauged)
117
Municipal Waste Water
86
Irrigated Agriculture Valley-Floor Turf
123 (86-160)
Albuquerque Storm Drain Inflow
6
Middle Rio Grande
Depletions
Discharge from Aquifer to Surface
167 (93-241)
271
Riparian Evapotranspiration (ET)
Shallow Aquifer
364
Recharge to Aquifer
In a warmer climateInflows decrease
anddepletions increase
Riparian ET, Irrigated Agriculture, Open
Water Evaporation
123 (99-222)
San Acacia Gauge
Elephant Butte Reservoir Evaporation
173 (49-281)
Dahm et al. (2002)
To Downstream Users
(370-1770)
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1 mm/d precip change ? 73 L/d change 1?C Tmax
change ? 15 L/d change
Water consumption in ABQ is sensitive to
temperature and precipitation variability
Annual consumption since 1931
Summer residential consumption changes regressed
onto T and P
Gutzler Nims (2005)
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The Impacts of Climate Change on Western Water
Resources
Warmer temperatures and continued (increased?)
variability Longer growing season . but
Surface water budget trends toward much drier
conditions Less snowpack ? less streamflow
in overallocated rivers More severe droughts
(perhaps more intense flooding too) ... all of
the above occurring as groundwater supplies
diminish
? HUGE water management challenges