Patterns of Intra-Seasonal Groundwater Recharge Inferred from Streamflow
and Explained by Vadose Zone Storage Deficits
Abstract
In forested, seasonally dry watersheds, winter rains commonly replenish
water storage 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 (driven
by evapotranspiration) alone insufficiently explain differences in the
wet season partitioning of rainfall due to the inter-storm behavior of
the deficit during the subsequent wet season. Tracking the deficit at
the storm event-scale within the wet season 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.