Groundwater loss tracked during drought in California’s Central Valley

Groundwater loss tracked during drought in California’s Central Valley.
A new study by researchers from UCLA and the University of Houston reveals significant groundwater loss in California’s Central Valley during the recent drought and sparks questions of sustainability for the important agricultural area.
The more recent drought accounted for more than 10 cubic kilometers of water lost per year.
Higher temperatures during the more recent drought period and the transition from row to tree crops, accounted for most of the increase in groundwater loss between the two droughts, and more than offset the effects of a reduction in irrigated land, Lettenmaier said.
Groundwater usage for crop irrigation in the Central Valley is a well-documented and hot-button issue in California.
Researchers used two methods to track groundwater levels, traditional water balance estimates — which take into account surface water inflow like rainfall and snow melt, soil moisture capacity and evapotranspiration — and data from NASA’s twin satellite system called GRACE (Gravity Recovery and Climate Experiment).
GRACE data estimates that groundwater loss from 2012 to 2016 was 11.2 cubic kilometers per year, compared to water balance estimates of 10 cubic kilometers per year.
"Although both water balance-based and GRACE-based groundwater volume estimates are subject to errors, the relatively small area of the Central Valley in the eyes of GRACE might also be responsible for that recovery discrepancy," Lee said.
Researchers hope future studies will address how much actual recovery happened between droughts and whether recovery from the most recent drought is on track to replenish the system.
Retrieved June 17, 2017 from University of California – Los Angeles.

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