Change in Water Resources in California During the 2011–2014 Drought Estimated Using GPS, GRACE, and InSAR

Abstract:

GPS is being used to weigh changes in total water storage in California [Argus Fu Landerer GRL 2014]. Each year the Sierra Nevada mountains rise about 12 mm in the Fall and Winter in response to the load of snow and rain, then rise about the same amount in the Spring and Summer when the snow melts, water runs off, and soil moisture evaporates. Earth's elastic response to a mass load is well known. Changes in total water can thus be determined as a function of location throughout California. The seasonal change (from Oct 1 to Apr 1) in equivalent water thickness is 0.5 m in the Sierra Nevada and decrease sharply to 0.1 m east into the Great Basin and west toward the Pacific coast.

In this study [Argus et al., ms in prep.] we use GPS to determine water change over the period of heavy precipitation from 2009 to 2011 and the current drought from 2011 to 2014. Changes in water in California's huge reservoirs are well known. We remove reservoir water changes from GPS vertical displacements, thus estimating the change in the sum of snow, soil moisture, and mountain fracture groundwater. We find water loss from Oct 2011 to Oct 2014 to be largest in the southern Sierra Nevada Mountains (0.8 m equivalent water thickness) and Klamath Mountains (0.5 m EWT). The time series for change in total water in the Sacramento–San Joaquin River basins is estimated with GPS to be 55 cubic km, of which 16 cubic km is reservoir water and 39 cubic km is soil moisture and mountain fracture groundwater. The time evolution of total water in the two river basins estimated from GPS is quite similar to that estimated from GRACE. Moreover, GPS is allowing water change during periods of heavy precipitation and drought to be inferred in smaller areas, such as the northern Sierras, southern Sierras, and Klamath mountains.