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DROUGHT RESILIENCE OF THE CALIFORNIA CENTRAL VALLEY SURFACE - GROUND - WATER-CONVEYANCE SYSTEM
<br />TABLE 11. Change in Average Ground -Water Level During a 60 -Year Drought and After a 30 -Year Recovery Period.
<br />and surface water diversions with CDWR's CALSIM
<br />model, and simulating the land surface, stream and
<br />aquifer response with CDWR's California Central
<br />Valley Ground water - Surface Water Simulation
<br />Model (C2VSIM). Three types of drought intensities
<br />were considered, 30% (light), 50% (moderate), and
<br />70% (severe) reductions in inflows to reservoirs, with
<br />reduced flow durations ranging from 10 to 60 years.
<br />Central Valley surface flow diversions decreased by
<br />12% under the slight drought scenario, and 38%
<br />under the severe drought scenario. In response to
<br />reduced surface water diversions and reduced rain-
<br />fall, ground -water pumping increased by 27% under
<br />the slight drought and by 71% under the severe
<br />drought. Net discharge from aquifers to rivers
<br />decreased by 23% for slight drought to 68% for severe
<br />droughts, and aquifer recharge decreased by 4% for
<br />slight droughts to 48% for severe droughts. The
<br />impacts on ground -water levels correlate with
<br />changes in ground -water storage, but are complicated
<br />by the compensating increase in pumping for highly
<br />irrigated regions (e.g., the San Joaquin Basin and
<br />Tulare Basin) with average Central Valley ground-
<br />water levels falling 17 in (53 ft) under the slight
<br />drought and 46 in (140 ft) under the severe drought.
<br />Simulated ground -water levels do not fully recover
<br />within 30 years after the end of the severe drought,
<br />and for the moderate and slight droughts a new equi-
<br />librium appears to be established.
<br />This study employed stationary 2003 -level agricul-
<br />tural and urban water demands to investigate the
<br />response of the ground -water flow system to long-
<br />term droughts. Future climate changes are expected
<br />to include many complex impacts on California's Cen-
<br />tral Valley that were not addressed in this study,
<br />including changes in the amount and timing of crop
<br />water demands as a result of increased mean temper-
<br />ature and evapotranspiration and increased atmo-
<br />spheric carbon (Brumbelow and Georgakakos, 2007;
<br />Kay and Davies, 2008), and changes in the timing
<br />and amounts of streamflow to reservoirs (Miller
<br />et al., 2003; Hayhoe et al., 2004; CDWR 2006; Milly
<br />et al., 2008). The impacts of these changes are diffi-
<br />cult to assess owing to the numerous and dynamic
<br />aspects of the ground -water flow system, including
<br />the spatial and temporal variability of recharge and
<br />interactions with surface water bodies and the land
<br />surface (Alley et al., 2002). This is further compli-
<br />cated because local changes in ground -water pump-
<br />ing, recharge, and other aspects of the hydrologic
<br />system may be significantly affected by changes in
<br />policies, societal values, and economic and technologi-
<br />cal factors (Loaiciga, 2003; Holman, 2006; King et al.,
<br />2008). This reduced form study gives a quantitative
<br />response to specified droughts that act as analogues
<br />to snowpack reduced inflows to reservoirs, and illus-
<br />trates the general impacts of climatic events on water
<br />storage under present day land use and population
<br />demands. Further study is required to determine the
<br />degree to which changes in agricultural demands in
<br />response to economic pressures would reduce ground-
<br />water depletion and promote more rapid recovery to
<br />pre - drought ground -water levels.
<br />ACKNOWLEDGMENTS
<br />This project was supported through a grant provided by the
<br />California Energy Commission, 500 -02 -004, and by the California
<br />Department of Water Resources. Work for the Department of
<br />Energy is under contract DE- ACO3- 76F00098.
<br />LITERATURE CITED
<br />Alley, W.M., R.W. Healy, J.W. LaBaugh, and T.E. Reilly, 2002.
<br />Flow and Storage in Groundwater Systems. Science 296:1985-
<br />1990.
<br />Anderson, J., F. Chung, M. Anderson, L. Brekke, D. Easton, M.
<br />Ejeta, R. Peterson, and R. Snyder, 2008. Progress on Incorporat-
<br />ing Climate Change Into Management of California's Water
<br />Resources. Climatic Change 87:591 -S108, doi 10.1007/s10584-
<br />007- 9353 -1.
<br />Benson, L., L. Braddock, J. Smoot, S. Mensing, S. Lund, S. Stine,
<br />and A. Sarna - Wojcicki, 2003. Influence of the Pacific Decadal
<br />Oscillation on the Climate of the Sierra Nevasa, California and
<br />Nevada. Quaternary Research 59:151 -159.
<br />Brumbelow, K. and A. Georgakakos, 2007. Consideration of
<br />Climate Variability and Change in Agricultural Water
<br />Resources Planning. Journal of Water Resources Planning and
<br />Management 133:275 -285.
<br />JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION 865 JAWRA
<br />Severe 60 -Year Drought
<br />Moderate 60 -Year Drought
<br />Slight 60 -Year Drought
<br />Hydrologic
<br />End
<br />-
<br />Recovery
<br />End
<br />Recovery
<br />End
<br />Recovery
<br />Region
<br />(m)
<br />(m) M
<br />(m)
<br />(m) M
<br />(m)
<br />(m)
<br />M
<br />Sacramento
<br />-10
<br />5.9 59
<br />-7.4
<br />3.9 53
<br />-3.3
<br />2.0
<br />60
<br />Eastside
<br />-20
<br />15 72
<br />-6.9
<br />6.6 96
<br />-4.7
<br />5.9
<br />>100
<br />San Joaquin
<br />-35
<br />21 59
<br />-15
<br />8.8 59
<br />-8.0
<br />7.9
<br />1
<br />Tulare
<br />-84
<br />2.6 3
<br />-67
<br />3.3 5
<br />-35
<br />2.3
<br />7
<br />Central Valley
<br />-46
<br />8.4 18
<br />-33
<br />4.9 15
<br />-17
<br />3.6
<br />21
<br />and surface water diversions with CDWR's CALSIM
<br />model, and simulating the land surface, stream and
<br />aquifer response with CDWR's California Central
<br />Valley Ground water - Surface Water Simulation
<br />Model (C2VSIM). Three types of drought intensities
<br />were considered, 30% (light), 50% (moderate), and
<br />70% (severe) reductions in inflows to reservoirs, with
<br />reduced flow durations ranging from 10 to 60 years.
<br />Central Valley surface flow diversions decreased by
<br />12% under the slight drought scenario, and 38%
<br />under the severe drought scenario. In response to
<br />reduced surface water diversions and reduced rain-
<br />fall, ground -water pumping increased by 27% under
<br />the slight drought and by 71% under the severe
<br />drought. Net discharge from aquifers to rivers
<br />decreased by 23% for slight drought to 68% for severe
<br />droughts, and aquifer recharge decreased by 4% for
<br />slight droughts to 48% for severe droughts. The
<br />impacts on ground -water levels correlate with
<br />changes in ground -water storage, but are complicated
<br />by the compensating increase in pumping for highly
<br />irrigated regions (e.g., the San Joaquin Basin and
<br />Tulare Basin) with average Central Valley ground-
<br />water levels falling 17 in (53 ft) under the slight
<br />drought and 46 in (140 ft) under the severe drought.
<br />Simulated ground -water levels do not fully recover
<br />within 30 years after the end of the severe drought,
<br />and for the moderate and slight droughts a new equi-
<br />librium appears to be established.
<br />This study employed stationary 2003 -level agricul-
<br />tural and urban water demands to investigate the
<br />response of the ground -water flow system to long-
<br />term droughts. Future climate changes are expected
<br />to include many complex impacts on California's Cen-
<br />tral Valley that were not addressed in this study,
<br />including changes in the amount and timing of crop
<br />water demands as a result of increased mean temper-
<br />ature and evapotranspiration and increased atmo-
<br />spheric carbon (Brumbelow and Georgakakos, 2007;
<br />Kay and Davies, 2008), and changes in the timing
<br />and amounts of streamflow to reservoirs (Miller
<br />et al., 2003; Hayhoe et al., 2004; CDWR 2006; Milly
<br />et al., 2008). The impacts of these changes are diffi-
<br />cult to assess owing to the numerous and dynamic
<br />aspects of the ground -water flow system, including
<br />the spatial and temporal variability of recharge and
<br />interactions with surface water bodies and the land
<br />surface (Alley et al., 2002). This is further compli-
<br />cated because local changes in ground -water pump-
<br />ing, recharge, and other aspects of the hydrologic
<br />system may be significantly affected by changes in
<br />policies, societal values, and economic and technologi-
<br />cal factors (Loaiciga, 2003; Holman, 2006; King et al.,
<br />2008). This reduced form study gives a quantitative
<br />response to specified droughts that act as analogues
<br />to snowpack reduced inflows to reservoirs, and illus-
<br />trates the general impacts of climatic events on water
<br />storage under present day land use and population
<br />demands. Further study is required to determine the
<br />degree to which changes in agricultural demands in
<br />response to economic pressures would reduce ground-
<br />water depletion and promote more rapid recovery to
<br />pre - drought ground -water levels.
<br />ACKNOWLEDGMENTS
<br />This project was supported through a grant provided by the
<br />California Energy Commission, 500 -02 -004, and by the California
<br />Department of Water Resources. Work for the Department of
<br />Energy is under contract DE- ACO3- 76F00098.
<br />LITERATURE CITED
<br />Alley, W.M., R.W. Healy, J.W. LaBaugh, and T.E. Reilly, 2002.
<br />Flow and Storage in Groundwater Systems. Science 296:1985-
<br />1990.
<br />Anderson, J., F. Chung, M. Anderson, L. Brekke, D. Easton, M.
<br />Ejeta, R. Peterson, and R. Snyder, 2008. Progress on Incorporat-
<br />ing Climate Change Into Management of California's Water
<br />Resources. Climatic Change 87:591 -S108, doi 10.1007/s10584-
<br />007- 9353 -1.
<br />Benson, L., L. Braddock, J. Smoot, S. Mensing, S. Lund, S. Stine,
<br />and A. Sarna - Wojcicki, 2003. Influence of the Pacific Decadal
<br />Oscillation on the Climate of the Sierra Nevasa, California and
<br />Nevada. Quaternary Research 59:151 -159.
<br />Brumbelow, K. and A. Georgakakos, 2007. Consideration of
<br />Climate Variability and Change in Agricultural Water
<br />Resources Planning. Journal of Water Resources Planning and
<br />Management 133:275 -285.
<br />JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION 865 JAWRA
<br />
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