Spatiotemporal Variability of Mountain Block Recharge in Three Semiarid Watersheds along the U.S.-Mexico Border Region

Abstract:

Groundwater recharge in semiarid mountains of the western U.S. remains a critical component of the regional water balance and has significant repercussions on water resources management, in particular during periods of drought. The bimodal distribution of annual precipitation in the southwest United States and northwest Mexico present a challenge as differential climate impacts during the winter and summer seasons are not currently well understood. In this work, we focus on the predictions of Mountain Block Recharge (MBR) using precipitation forcing from a reanalysis product, regional climate model-based precipitation products and available ground observations. MBR estimates in the Santa Cruz, San Pedro and Sonora River basins (>40,000 km2) are compared along a north to south gradient crossing the U.S.-Mexico border. As a result of the influence of the North American monsoon, the impact of seasonality in each of these systems is evaluated. Simulated precipitation fields under historical (1991-2000) conditions and climate change (2031-2040 and 2070-2080) scenarios are compared at resolutions of 10-km and 35-km as generated from the Weather Research and Forecast (WRF) model using boundary conditions from two general circulation models (MPI-ECHAM and HadCM3). Mountain subbasins to apply a seasonal MBR method were delineated using a threshold in terrain slope that matched official boundaries of known aquifers in these transboundary watersheds. We evaluated the MBR outcomes from the various precipitation products to quantify biases involved in the historical estimates and to inform groundwater management on the uncertainties inherent in future projections. We also inspect the variability of MBR across pluvial and drought periods lasting several years. Seasonal comparisons across a north to south spatial gradient yield a valuable assessment on the impacts of climate change on MBR for important basins in the U.S.-Mexico border region.