Alpine foreland running drier? Sensitivity of a drought vulnerable catchment to changes in climate, land use, and water management

Abstract

Southeastern Austria as part of the southeastern Alpine forelands experiences an increase of temperature and a tendency of decreasing precipitation. Especially in summer, the temperature strongly increased by about 0.7°C per decade since the 1970s. Drought vulnerability under climate change is therefore a key question in this region. Here, we address this question by exploring the hydrological sensitivity of the Raab catchment in Austria (area 987 km 2), a typical catchment in these Alpine forelands. Using the process-oriented Water Flow and Balance Simulation Model (WaSiM) over 1982-2011, we focus on low-flow conditions during extended summer (May-September) and analyze the catchment's runoff sensitivity to climate change, but also land use and water management change. We find that climate change drivers dominate the summertime runoff response (decrease > 40/> 70%), based on moderate and strong climate change cases in the region (temperature + 2/+ 4 K, precipitation − 15/− 30%). Land use changes towards more dry and sealed areas enhance surface runoff and thus may lead to somewhat increased flood peaks. In contrast, water withdrawal for irrigation reduces runoff during low-flow periods in the summer when the irrigation demand is high. Although the impact of these non-climatic drivers on runoff generally is lower than that of the climate change considered, their interactive effects may reinforce the catchment's tendency of running drier during summer. While more detailed

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“…There is a rich literature on simulating runoff from hydrologic basins, ranging from strongly process-based models (Hohmann et al 2018) to semi-distributed hydrologic routing models (Buccola et al 2016) and highly-parameterized conceptual models (Nauditt et al 2017). A critical challenge for runoff models is obtaining the data needed to discretize the simulation domain, represent highly variable properties and processes at appropriate temporal and spatial scale(s), and calibrate/validate the model against hydrologic observations (Cornelissen et al 2016).…”

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“…The terrain of the FBR is hilly and characterized by small differences in altitude, and the region is quite sensitive to climate change (Kabas et al, 2011;Kabas, 2012;Hohmann et al, 2018). It exhibits rich weather variability, especially including strong convective activity and severe weather in summer (Kirchengast et al, 2014;Kann et al, 2015;O et al, 2017, 2018. Recently, Schlager et al (2017) also analyzed wind fields in this region.…”