Satellite-based monitoring of groundwater depletion in California\u2019s Central Valley

Donald W Vasco,Pierre Jeanne,Tom G Farr,Christine Doughty,Peter Nico

doi:10.1038/s41598-019-52371-7

Abstract

Range change data, obtained from Synthetic Aperture Radar satellites, form the basis for estimates of aquifer volume change in California’s Central Valley. The estimation algorithm incorporates a function penalizing changes far from known well locations, linking the aquifer volume changes to agricultural, industrial, and municipal pumping within the Tulare basin. We show that the range changes are compatible with the hypothesis that the source of aquifer volume changes are variations in effective pressure around documented wells. Specifically, inclusion of the well distance penalty does not degrade the fit to the observations, inversions with and without it both give variance reductions of 99.6%. The patterns of aquifer volume change vary significantly from the drought year, between October 2015 and October 2016, to a wet year in 2017, and into 2018, a year with near average rainfall. The 2.3 million acre-feet of estimated volume reduction, a lower bound on the amount of water extracted from the basin between October 2015 and 2016, agrees with independent estimates of 1.8 and 2.3 million acre-feet. The aquifer volume reduction is also compatible with a loss of 3.1 km3 (2.5 million acre-feet) in groundwater volume derived from Gravity Recovery and Climate Experiment (GRACE) satellite data.

Highlights

Range change data, obtained from Synthetic Aperture Radar satellites, form the basis for estimates of aquifer volume change in California’s Central Valley
Satellite-based Interferometric Synthetic Aperture Radar (InSAR) data have been used to image surface deformation associated with groundwater withdrawal and replenishment[11,12,13]
We describe the outcome of our analysis of the InSAR data using the inversion techniques described in the Methods section

Summary

Introduction

Range change data, obtained from Synthetic Aperture Radar satellites, form the basis for estimates of aquifer volume change in California’s Central Valley. Crop type and crop water-intensity, along with well density, have been used to estimate the expected water usage, and these factors correlate with observed surface subsidence[4,5], and observed changes in groundwater storage[6] Such an approach can be combined with high-resolution Landsat satellite images to determine the distribution and health of crops more accurately[7]. Satellite-based Interferometric Synthetic Aperture Radar (InSAR) data have been used to image surface deformation associated with groundwater withdrawal and replenishment[11,12,13] Such techniques have proven useful in California’s Central Valley and identify large-scale subsidence due to groundwater pumping and potential hazards to existing infrastructure[14,15,16,17]. This last step typically requires data that are difficult to gather and are likely to be unavailable, including the minimum effective pressure that the aquifer has ever been subjected to[21,22,23], though there have been efforts to reformulate the problem to make inferences directly from InSAR range change, water level, and geological data[24]

Methods

Results

Conclusion