Stress testing as complement to climate scenarios: Recharge scenarios to quantify streamflow drought sensitivity

Abstract

Precipitation deficits and temperature anomalies are often the main cause for low flows and summer streamflow droughts. However, where groundwater is the main contribution to sustain water availability and ecological integrity during dry spells, the role of recharge and catchment storage is crucial to understand streamflow drought sensitivity. Here we introduce recharge stress tests as complement to climate scenarios to characterize and quantify the streamflow drought sensitivities of catchments. The stress tests are presented by applying them to six headwater catchments in Switzerland with various catchment and streamflow characteristics. The stress tests drive the bucket-type hydrological model HBV in a framework, in which pre-drought recharge conditions can be decreased to test how catchments respond to and recover from drought. We identified an upper limit of stress test durations around 12 months as indicator of maximum recharge- and storage-memory for the study catchments. Varying response on stress testing across the catchments suggests different storage properties and thus different recovery times from drought. From the stress test simulations, we found up to 200d longer summer streamflow droughts with additional streamflow deficits which account for up to 40d of median flow. Using a worst-case pre-drought recharge in stress test simulation leads to minimum flow reductions of 50%-80% compared with the reference simulation. Based on the results we conclude with recommendations for further stress test research in drought hydrology.