Abstract
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 200 d longer summer streamflow droughts with additional streamflow deficits which account for up to 40 d 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.
Highlights
To assess the sensitivity of catchments to drought it is important to understand how hydrological systems might respond to changes in future climate
In this study we present a hydrological model experiment to stress pre-drought recharge in order to test drought sensitivity across several headwater catchments in Switzerland
Varying stress test (ST) durations show that the six study catchments have a recharge/storage-memory of around 6 to 12 months when focusing on summer low flows
Summary
To assess the sensitivity of catchments to drought it is important to understand how hydrological systems might respond to changes in future climate. Different temporal structures of future climate input can affect low flows, but the sequencing of simulated wet and dry spells is not altered (Vormoor et al, 2017). Climate change scenarios introduce large uncertainties to hydrological assessment of future streamflow droughts and low flow events (Addor et al, 2014). A way forward to reduce these uncertainties is a generic model framework in which climate input of a reference simulation from a hydrological model can be altered to test the response of catchments regarding periods with low streamflow (Stoelzle et al, 2014; Staudinger et al, 2015). In the stress test (ST) framework pre-drought recharge is reduced while the catchment-specific climate variability is preserved. Through alteration of pre-drought recharge and water availability, a new sequencing in drought propagation is tested
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