The utility of satellite-based data in improving groundwater management in agricultural regions was demonstrated in the California Central Valley. University of California San Diego researchers combined land cover and climate data with interferometric synthetic aperture radar (InSAR) data to link rates and patterns of land surface displacement to the differential groundwater demand generated by different land uses and associated irrigation.

InSAR was used to make high-resolution maps of land surface motion in space and time, including measurement of subsidence patterns according to crop type. Despite reports of high water consumption by fruit and nut crops in California, the crop types with the greatest rates of subsidence, and by association the greatest rates of groundwater use, were field crops such as corn and soy, followed by pasture crops like alfalfa, truck crops like tomatoes, and lastly fruit and nut crops like almonds and grapes.Subsidence occurred at much higher rates in irrigated cultivated land compared to undeveloped land, and in dry surface water-limited years relative to wet years. Source: Morgan C. Levy et al.

Combining InSAR with other land surface datasets for the 2015 to 2017 period including land cover, potential evapotranspiration and the location of surface water supply networks revealed that subsidence occurred at much higher rates in irrigated cultivated land compared to undeveloped land and in dry surface water-limited years relative to wet years. The study documents a median 272 mm of total cumulative subsidence for field crops and a dry water year subsidence rate of 131 mm per year. A median 62 mm of total subsidence and a dry water year subsidence rate of 31 mm is indicated for fruit and nut crops.

A transition to fruit and nut cultivation appears preferable in terms of groundwater sustainability. The research published in Environmental Research Letters shows InSAR to be a promising source of spatially consistent geophysical data relevant to water resources management because it records the land surface response to water storage changes at unprecedented spatial and temporal resolutions.