A three-pillar approach to assessing future low flows in Austria | Ein Drei-Standbeine-Ansatz zur Ermittlung zukünftiger Niederwasserabflüsse in Österreich

Accurately predicting future low flows offers an important basis for water management and environmental policy. However, given the considerable degree of uncertainty involved in current climate prognoses, alternative sources of information should also be taken into account. Accordingly, an innovative three-pillar approach was developed in the context of the interdisciplinary research project Climate Impacts On Low Flows And Droughts (CILFAD), an approach detailed in this paper. The first pillar of the climate change analysis consists in trend analyses of 408 stream gauges in Austria and neighboring regions of Bavaria, Slovakia and Hungary, which include both spatial and temporal aspects. In turn, the second pillar involves ensemble projections of climate scenarios on the basis of water balance models that reflect the uncertainties inherent in modeling. The third pillar is an innovative approach that couples the water balance models with stochastic simulations of those climate parameters most essential to the water balance.In the course of the three-pillar approach, the individual analyses are combined, a process in which both the expected values and the uncertainties of the respective methods are reflected. The analyses indicate that in the Alps winter low flow discharges will likely increase in response to rising temperatures. This statement can be considered relatively reliable, given the fact that the different sources of available information agree and a temperature-based increase can be fairly well predicted. Predictions for lowland regions are less reliable , as they involve changes in precipitation that are considerably more difficult to predict. The lowland regions of eastern and southeastern Austria are the most likely candidates for a summertime decrease in low flows, which would have adverse effects on available water resources. In contrast, there are unlikely to be any significant changes concerning low flows in northern Austria, and only small changes in southwest Austria. The results of the study are based on a range of different sources of information, making it more robust than individual analyses, which are normally based on either observed trends or on climate projections.