WARMING TRENDS AND GROUNDWATER
RECHARGE IN WESTERN MOUNTAINS
WITH IMPLICATIONS FOR GROUNDWATER
AND SURFACE-WATER RESOURCES
Sam Earman1 and Michael Dettinger2
1Desert Research Institute, Reno, NV
2US Geological Survey, La Jolla, CA
Is it worth looking at warming impacts on
groundwater in the western USA?
Is it worth looking at warming impacts on
groundwater in the western USA?
YES, IF:
•Groundwater is an important resource for
the West
Is it worth looking at warming impacts on
groundwater in the western USA?
YES, IF:
•Groundwater is an important resource for
the West
•Our current knowledge suggests that
warming has the potential to impact
groundwater resources
Is groundwater an important resource?
Total water use in the western states (excluding
thermoelectric power generation)
Surface
water:
72%
Groundwater:
28%
(calculated from data in Hutson et alii, 2004)
Is groundwater an important resource?
Irrigation use in the western states
Surface
water:
74%
Groundwater:
26%
(calculated from Hutson et alii, 2004)
Is groundwater an important resource?
Public/municipal water supply in the western states
Surface
water:
57%
Groundwater:
43%
(calculated from data in Hutson et alii, 2004)
Is groundwater an important resource?
Yes!
Is groundwater an important resource?
Yes! But not just for humans:
(image source: http://www.machinearts.com/sclr9-01/pages/springs4.htm)
Is groundwater an important resource?
Yes! It’s also vital to surface-water systems:
“Old” concept of streamflow
(after Hewlett, 1982)
Is groundwater an important resource?
Yes! It’s also vital to surface-water systems:
“New” concept of streamflow
(after McDonnell, 2004)
Is it worth looking at warming impacts on
groundwater in the western USA?
YES, IF:
9
•Groundwater is an important resource for
the West
•Our current knowledge suggests that
warming has the potential to impact
groundwater resources
Does warming have the potential to affect groundwater?
Topography
(US Geological Survey)
Precipitation
(Western Regional Climate Center)
Schematic diagram of groundwater recharge
UNSATURATED
SATURATED
Schematic diagram of groundwater recharge
Rain: small amount,
intermittent
UNSATURATED
SATURATED
Schematic diagram of groundwater recharge
Rain: small amount,
intermittent; often not
enough for recharge
UNSATURATED
SATURATED
Schematic diagram of groundwater recharge
Snow: archives or
“banks” many events
UNSATURATED
SATURATED
Schematic diagram of groundwater recharge
Snow: archives or
“banks” many
events; often enough
for recharge
UNSATURATED
SATURATED
Does warming have the potential to affect groundwater?
Study sites for estimating groundwater
recharge derived from snowmelt
S: Steward Observatory
C: Chiricahua Mts.
L: Los Alamos
M: Magdalena
Seasonal variation in isotope content of precipitation
-40
Analytical precision:
δ 18O: 0.1 per mill
δ 2H: 1.0 per mill
δ D, per mill
-60
Summer
Precip
-80
Local
groundwater
-100
Winter
Precip
-120
-140
-18
-16
-14
-12
δ 18O, per mill
-10
-8
Does warming have the potential to affect groundwater?
Percentage of groundwater recharge
derived from snowmelt
Site
20022003
20032004
Long
term
Precip.
%
Chiricahuas
-
-
60
30
Los Alamos
54
48
-
41
Magdalena
51
69
-
49
Steward
-
43
-
25
(Earman, 2004)
Does warming have the potential to affect groundwater?
Locations of sites where snowmelt is directly or
indirectly shown to account for significant
proportions of groundwater recharge
Winograd et alii (1998); Szecsody et alii (1983); James et alii (2000); Manning (2002); Earman (2004)
Using dissolved gases in groundwater to determine
recharge elevation
ATMOSPHERE: well mixed, known gas
concentrations [Xi = k]
UNSATURATED
SATURATED
Using dissolved gases in groundwater to determine
recharge elevation
ATMOSPHERE: well mixed, known gas
concentrations [Xi = k]
UNSATURATED
SOIL GAS: for inert gases,
concentrations are nearly identical to
those in the atmosphere [Xi = k]
SATURATED
Using dissolved gases in groundwater to determine
recharge elevation
ATMOSPHERE: well mixed, known gas
concentrations [Xi = k]
UNSATURATED
SOIL GAS: for inert gases,
concentrations are nearly identical to
those in the atmosphere [Xi = k]
SATURATED
GROUNDWATER: gas concentration is a
function of soil gas conc. and environmental
parameters (T and elevation)—Henry’s Law
E-W profile of the Chiricahua Mts. with calculated
groundwater recharge elevations
Elevation above sea level (m)
3000
2500
2000
1500
-109.30
-109.25
-109.20
Degrees west of prime meridian
-109.15
E-W profile of the Chiricahua Mts. with calculated
groundwater recharge elevations
Elevation above sea level (m)
3000
2500
2000
1500
-109.30
-109.25
-109.20
Degrees west of prime meridian
-109.15
Linear trends in April 1 snow water equivalent, 1950-1997
relative to the starting value for the linear fit
-80%
+80%
-60%
+60%
-40%
+40%
-20%
+20%
(Mote, 2004)
Reduction in Colorado River basin snow water equivalent
(Based on a 1.7 °C increase in T)
(Christensen et alii, 2004)
PRISM precipitation data
Typical snow
line
PRISM precipitation data
Increase temperature
2 °C
(assuming lapse rate
of 5 °C/1000 m)
New snow
line
Loss in
snow-covered area
PRISM precipitation data
Increase temperature
2 °C
(assuming lapse rate
of 5 °C/1000 m)
New snow
line
Loss in
snow-covered area
20% snow loss
due to snow-rain
shift
Is it worth looking at warming impacts on
groundwater in the western USA?
YES, IF:
9
9
•Groundwater is an important resource for
the West
•Our current knowledge suggests that
warming has the potential to impact
groundwater resources
Summary
•Groundwater is a vital resource for the West
Summary
•Groundwater is a vital resource for the West
“Direct” importance (groundwater use
from wells/springs)
“Indirect” importance—streamflow
Summary
•Groundwater is a vital resource for the West
“Direct” importance (groundwater use
from wells/springs)
“Indirect” importance—streamflow
•Groundwater recharge is highly dependant on
snow
Summary
•Groundwater is a vital resource for the West
“Direct” importance (groundwater use
from wells/springs)
“Indirect” importance—streamflow
•Groundwater recharge is highly dependant on
snow
•For most areas of the West, a significant shift
from snow to rain is predicted over the
next 50 yr
Summary
•Warming is very likely to have significant
impacts on groundwater systems
Summary
•Warming is very likely to have significant
impacts on groundwater systems
•Given the importance of groundwater to the
West, further investigation of warming
impacts on groundwater is vital
Groundwater recharge mechanisms
How will input to streams and streamflow be affected?
How will altered streamflow affect basin floor groundwater
recharge?
How will basin aquifers be impacted?
(Baillie et alii, 2003)
Summary
•Warming is very likely to have significant
impacts on groundwater systems
•Given the importance of groundwater to the
West, further investigation of warming
impacts on groundwater is vital
•Monitoring strategies for detecting and
tracking these changes are needed
--Modern geochemical methods may
be most appropriate