A REMOTE SENSING MASS BALANCE APPROACH TO ESTIMATING SPATIAL RECHARGE IN CALIFORNIA'S CENTRAL VALLEY AQUIFERS

Hydrogeologists have long attempted to estimate aquifer recharge to gain insight into the water balance of the aquifer, as well as to make important and sustainable groundwater management decisions. In California’s Central Valley, the task of managing a burgeoning, groundwater-based agriculture sector amidst drought brings a critical significance to estimating recharge input into regional aquifers.

Traditionally, in estimating recharge, a set of borehole geochemical measurements or point-scale infiltration tests are conducted to derive a representative recharge rate over the region. Often in numerical hydrogeological models, a single recharge rate is applied over an entire basin. Realistically, the spatially complex interplay of varying precipitation, evapotranspiration, and soil hydrology form a diverse landscape of non-uniform recharge; neglecting this non-uniformity in management and modeling can introduce unintended albeit significant errors.

We apply a remote sensing-based, mass balance approach to evaluate the monthly to annual recharge to the regions of the California Watershed, focusing on the Central Valley. Using datasets from the TRMM and AMSR-E satellite missions combined with NLDAS model output in a mass balance equation, we the estimate monthly recharge on the 0.125x0.125 degree scale. We validate our model by comparing annual estimated recharge in the Central Valley to previous approaches using tracer age-velocity estimates, and find good agreement from the comparisons.

We further compare the estimated recharge between regions and other significant variables for various relationships. Annual recharge of each of the Central Valley aquifers generally follows the same trend; however, distinct differences are found between the amount of recharge in each basin, with recharge rates increasing from the northern part of the Valley southward. Further delineation is found on the monthly time scale. Distributions of precipitation versus corresponding recharge are also compared in an effort to classify the recharge potential of various regions.