ABSTRACT:

In forested, seasonally dry watersheds, winter rains commonly replenish moisture deficits in the vadose zone before recharging underlying hillslope groundwater systems that sustain streamflow. However, the relative inaccessibility of the subsurface has hindered efforts to include the role of storage deficits, primarily generated by plant-water uptake, in moderating groundwater recharge. Here, we compare groundwater recharge inferred from the storage-discharge relationship with independent, distributed estimates of vadose zone storage deficits across 12 undisturbed California watersheds, thereby tracking the evolution of the deficit-recharge relationship without intensive field instrumentation. We find accrued deficits during the dry season alone insufficiently explain differences in the wet season partitioning of rainfall due to the non-monotonic behavior of the deficit during the subsequent wet season. Tracking the deficit at the storm event-scale within the wet season, however, reveals a characteristic response in groundwater to increasing rainfall not captured in the seasonal analysis, and may improve estimates of the rainfall required to generate recharge and streamflow on a per-storm basis. Our findings demonstrate the potential for existing public datasets to better capture water partitioning within the subsurface using a combined deficit-recharge approach, though our analysis is currently limited to basins with select characteristics.

CODE AVAILABLE ON GITHUB: https://github.com/noah-beniteznelson/recharge_deficit