Simulating groundwater surface water interactions across the continental US with an integrated hydrologic model

Lateral groundwater flow redistributes moisture through the subsurface, supporting direct exchanges with surface water bodies and evapotranspiration at the land surface. While these connections are well established and there is a growing focus on the importance of groundwater surface water exchanges, there are still many uncertainties regarding the role of groundwater across spatial scales in large physically based models. Here we use an integrated hydrologic model to evaluate the impact of groundwater on plant water availability across the continental US. Analysis is based on a high-resolution (1km2 lateral resolution) simulation of the majority of the contiguous US (roughly 6.3 million km²). We quantify behavior using multiple transient simulations generated using hourly historical observed meteorology from a gridded reanalysis product. Baseline simulations are compared to warming scenarios that start from the same pre-development steady state groundwater configuration but with a series of constant temperature perturbations applied. Comparative analysis demonstrates spatial patterns in the sensitivity of land surface dynamics to warming that vary with groundwater depth and aridity as well as hydro-geologic settings where groundwater surface water exchanges dampen or amplify the combined response of the integrated system. Furthermore, aggregating the high-resolution outputs, we quantify the dependence of simulated interactions on spatial scale. Our results highlight the variable role of groundwater surface water interactions in large integrated simulations across physical settings and spatial scales.