The importance of scale-dependent groundwater processes in land-atmosphere interactions over the central United States

Observations are compared to multiscale Weather Research and Forecasting (WRF) simulations of three summer seasons: 2012, 2013, and 2014. Results show that a grid spacing of 3 km or smaller is necessary to capture small-scale river and stream networks and associated shallow water tables, which supplies additional root-zone water double that of simulations with 9-km and 27-km grid spacing and is critical to replenishing the depleted vegetation root zones and leads to 150 mm more evapotranspiration.

Including groundwater processes in convection-permitting models is effective to reduce: (1) 2-m temperature warm biases from 5-6 to 2-3 degrees C and (2) the low precipitation bias by half. The additional groundwater supply to active soil flux in convection-permitting simulations with groundwater for June-August is nearly translated into the same amount of increased precipitation in the domain investigated.