Auxiliary material for the manuscript 2014GL061055
Groundwater Depletion During Drought Threatens Future Water Security of the Colorado
River Basin
Stephanie L. Castle1,2, Brian F. Thomas1, 2,3, John T. Reager1, 2,3, Matthew Rodell4, Sean C.
Swenson5, and James S. Famiglietti*1, 2, 3
1
UC Center for Hydrologic Modeling, University of California, Irvine, CA, 92697, USA
2
Department of Earth System Science, University of California, Irvine, CA, 92697, USA
3
NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, 91109, USA
4
Hydrological Sciences Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, 20771,
USA
5
Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, CO,
80303, USA
*
Corresponding author: jfamigli@uci.edu
Geophysical Research Letters, 2014
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This auxiliary material contains four additional figures that support the main text. Figure S1
portrays the comparison of GRACE-derived total water storage change to a traditional water
balance estimate of total water storage change. In Figure S2 we utilize GRACE total water storage
to solve for accessible water in the Basin by removing soil moisture and snow water equivalent.
The residual accessible water is shown in Figure S3. After separating the components of accessible
water, which include reservoir and groundwater storage, a trend analysis of groundwater storage
changes was conducted revealing significant negative trends in groundwater throughout the Basin
shown in Figure S4.
Figure Captions
Figure S1. (A) GRACE-derived terrestrial water storage change (blue) and water balance estimate
of observed terrestrial water storage change (red) from March 2005 to March 2010 for the entire
Basin. (B) Same as (A) but for the Upper and (C) Lower Basins. The blue shading represents error
in the GRACE dS/dt estimate. The red shading represents uncertainty in the water balance
estimate.
Figure S2. (A) Monthly anomalies (km3) of soil moisture storage (brown) (no significant trend)
and of SWE (dark blue) (no significant trend) for the entire Basin; (B) the Upper Basin soil
moisture storage (no significant trend) and SWE (no significant trend); and (C) the Lower Basin
soil moisture storage (-0.9 ± 0.2 km3 yr-1) and SWE (no significant trend), from December 2004
to November 2013. Errors are shown in light brown shading for soil moisture storage and in light
blue shading for SWE storage. All trends are summarized in Table 1.
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Figure S3. (A) Monthly anomalies (km3) of GRACE-derived accessible water (i.e. groundwater
anomalies plus surface water anomalies) for the entire Basin. There is a significant trend (-5.4 ±
0.5 km3 yr-1) from December 2004 to November 2013. (B) Same as (A) but for the Upper (-1.1 ±
0.4 km3 yr-1) and (C) Lower Basins (-3.0 ± 0.3 km3 yr-1). Errors are shown in light green shading
for accessible water storage. All trends are summarized in Table 1.
Figure S4. Monthly anomalies (km3) of groundwater storage and their respective error (light gray
shading) for the (A) entire Basin; (B) Upper Basin; and (C) the Lower Basin, from December
2004-November 2013. Blue lines represent trends in groundwater storage changes for the entire
(-5.6 ± 0.4 km3 yr-1), Upper (-1.7 ± 0.4 km3 yr-1) and Lower (-2.6 ± 0.3 km3 yr-1) Basins from
December 2004-November 2013. Red lines represent piecewise trends for the entire (-6.3 ± 0.9
km3 yr-1), Upper (-1.9 ± 0.8 km3 yr-1) and Lower (-4.1 ± 0.6 km3 yr-1) Basins from December 2004January 2010 and for the entire (-10.9 ± 1.5 km3 yr-1), Upper (-6.1 ± 1.5 km3 yr-1) and Lower (-5.8
± 0.9 km3 yr-1) Basins February 2010-November 2013. Important trends are reported in the text
and summarized in Table 1.
3
Figure S1. (A) GRACE-derived terrestrial water storage change (blue) and water balance estimate
of observed terrestrial water storage change (red) from March 2005 to March 2010 for the entire
Basin. (B) Same as (A) but for the Upper and (C) Lower Basins. The blue shading represents error
in the GRACE dS/dt estimate. The red shading represents uncertainty in the water balance
estimate.
4
Figure S2. (A) Monthly anomalies (km3) of soil moisture storage (brown) (no significant trend)
and of SWE (dark blue) (no significant trend) for the entire Basin; (B) the Upper Basin soil
moisture storage (no significant trend) and SWE (no significant trend); and (C) the Lower Basin
soil moisture storage (-0.9 ± 0.2 km3 yr-1) and SWE (no significant trend), from December 2004
to November 2013. Errors are shown in light brown shading for soil moisture storage and in light
blue shading for SWE storage. All trends are summarized in Table 1.
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Figure S3. (A) Monthly anomalies (km3) of GRACE-derived accessible water (i.e. groundwater
anomalies plus surface water anomalies) for the entire Basin. There is a significant trend (-5.4 ±
0.5 km3 yr-1) from December 2004 to November 2013. (B) Same as (A) but for the Upper (-1.1 ±
0.4 km3 yr-1) and (C) Lower Basins (-3.0 ± 0.3 km3 yr-1). Errors are shown in green shading for
accessible water storage. All trends are summarized in Table 1.
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Figure S4. Monthly anomalies (km3) of groundwater storage and their respective error (light gray
shading) for the (A) entire Basin; (B) Upper Basin; and (C) the Lower Basin, from December
2004-November 2013. Blue lines represent trends in groundwater storage changes for the entire
(-5.6 ± 0.4 km3 yr-1), Upper (-1.7 ± 0.4 km3 yr-1) and Lower (-2.6 ± 0.3 km3 yr-1) Basins from
December 2004-November 2013. Red lines represent piecewise trends for the entire (-6.3 ± 0.9
km3 yr-1), Upper (-1.9 ± 0.8 km3 yr-1) and Lower (-4.1 ± 0.6 km3 yr-1) Basins from December 2004January 2010 and for the entire (-10.9 ± 1.5 km3 yr-1), Upper (-6.1 ± 1.5 km3 yr-1) and Lower (-5.8
± 0.9 km3 yr-1) Basins February 2010-November 2013. Important trends are reported in the text
and summarized in Table 1.
7