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Groundwater depletion in California's Central Valley accelerates during megadrought - PubMed

  • ️Sat Jan 01 2022

Groundwater depletion in California's Central Valley accelerates during megadrought

Pang-Wei Liu et al. Nat Commun. 2022.

Abstract

Groundwater provides nearly half of irrigation water supply, and it enables resilience during drought, but in many regions of the world, it remains poorly, if at all managed. In heavily agricultural regions like California's Central Valley, where groundwater management is being slowly implemented over a 27-year period that began in 2015, groundwater provides two-thirds or more of irrigation water during drought, which has led to falling water tables, drying wells, subsiding land, and its long-term disappearance. Here we use nearly two decades of observations from NASA's GRACE satellite missions and show that the rate of groundwater depletion in the Central Valley has been accelerating since 2003 (1.86 km3/yr, 1961-2021; 2.41 km3/yr, 2003-2021; 8.58 km3/yr, 2019-2021), a period of megadrought in southwestern North America. Results suggest the need for expedited implementation of groundwater management in the Central Valley to ensure its availability during the increasingly intense droughts of the future.

© 2022. The Author(s).

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1. California’s Central Valley.

The Central Valley (green) encompasses the Sacramento, San Joaquin, and Tulare Basins (black and white boundary). The red border outlines the area of GRACE/FO mascon data used for the study. Blue dots show locations of active reservoir storage gauges distributed within the study region, and the orange and brown dots show locations of the two main stream discharge gauges in Central Valley. The GRACE/FO data, reservoir storage and streamflow measurements are used to estimate groundwater storage changes as discussed in the Methods section.

Fig. 2
Fig. 2. Datasets used for groundwater storage anomaly calculation and GRACE/FO data evaluation in the Central Valley.

a GRACE/FO observed monthly total water storage (TWS) anomalies. Red arrow indicates the driest winter in TWS for the past two decades at the begining of 2021. b Three water balance fluxes of precipitation (P), evapotranspiration (ET), and streamflow (Q). c Comparison of monthly change in TWS (dS/dt) between that derived from GRACE/FO and from an observed water balance. d Anomalies of three TWS components of soil moisture (SM), surface water (SW), and snow water equivalent (SWE). All variables are represented in equivalent water height in millimeters for the study region.

Fig. 3
Fig. 3. Groundwater storage variations in California’s Central Valley.

a GRACE/FO-derived groundwater storage anomalies from September 2003–December 2021 in the Central Valley. The green shaded margin is the uncertainty of groundwater storage. Red arrows represent groundwater loss trends during the droughts of 2006–2011, 2011–2017, and since 2019. Blue arrows represent the three short recharge periods. The black line shows the groundwater depletion trend from 2003–2021. b comparison of deseasonalized anomalies of GRACE/FO derived groundwater and water table depth anomalies from monitoring wells in the Central Valley.

Fig. 4
Fig. 4. Yearly cumulative groundwater losses in the Central Valley.

Groundwater losses combining the USGS’s Central Valley Hydrologic Model (CVHM) and the GRACE/FO estimates since 1962. The black line represents the overall groundwater depletion from 1962 to 2021 calculated by combining the CVHM and GRACE estimates.

Fig. 5
Fig. 5. Groundwater and surface water management in Central Valley.

a Comparison between annual surface water allocations in the aqueducts of the California State Water Project (SWP) and the federal Central Valley Water Project (CVP) and GRACE/FO-derived groundwater storage anomalies. b Comparison between annual surface water deliveries (dark blue bars) of SWP and CVP to the GRACE/FO derived groundwater changes (red and green bars) in Central Valley. The groundwater changes in 2003, 2017, and 2018 are not included because GRACE/FO-derived data do not have complete coverage over the year.

Fig. 6
Fig. 6. Groundwater storage variations in the three Central Valley sub-basins.

GRACE/FO-derived groundwater anomalies during September 2003–December 2021 in the (a) Sacramento, (b) San Joaquin, and (c) Tulare basins. The green shaded margins are the uncertainty of groundwater storage estimates. Red arrows represent groundwater loss trends during the droughts of 2006–2011, 2011–2017, and since 2019. Blue arrows represent the three short recharge periods. The black line shows the overall groundwater depletion trend from 2003–2021. Comparison of deseasonalized anomalies of GRACE/FO derived groundwater and water table depth anomalies from monitoring wells for the (d) Sacramento, e San Joaquin, and (f) Tulare basins.

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