Water Table Response to Extreme Precipitation Events

Precipitation patterns are projected to shift from low-intensity, long duration to high-intensity, fast duration due to climate change. These high-intensity events, known as extreme precipitation events (EPEs), will impact groundwater resources. The subsurface is the link between EPEs and groundwater, where soil hydraulic properties influence infiltration from the surface to the water table. Unfortunately, subsurface response to EPEs remains poorly understood. Recent studies have found that EPEs can lead to elevated water tables for over a year after an event. To better understand the role of subsurface processes in controlling EPE-driven infiltration to the water table, we examine water table response to EPEs across sites of various climates and with varying soils throughout the United States. Local precipitation data is used to characterize EPEs, defined as a 1-day precipitation event with annual exceedance probabilities of 0.1%. The inverse solution in the HYDRUS-1D modeling software is used to obtain the soil-water retention curve for each site. Normal and EPE cases are modeled and compared to examine water table displacement (ΔWTD) and recession time (trec). The ΔWTD range from 0.70 to 2.40 m across sites and are not directly controlled by EPE amount; instead, ΔWTD is inversely related to available porosity. Soils with low available porosity undergo large ΔWTD compared to soils with higher available porosity. Despite larger EPEs, modeled water tables in wetter regions such as the Atlantic Plains and Appalachian Highlands recede faster than those of the drier Interior Plains and Intermontane Plateau. We find that water table recession times, trec, are inversely related to hydraulic diffusivity. For all cases, trec ranges from months to years suggesting an increased role by the subsurface in buffering EPEs. A hydrologic buffer could have important benefits for water-limited regions in times of drought.