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Headwater catchments are the "water towers" to many lowland regions. They receive comparably higher precipitation and in times of extended meteorological drought, catchments can sustain streamflow from their natural storages. This colloquium presentation gives an overview of the hydrological processes that become particularly relevant in drought situations, including for example streamflow contributions from mountain headwaters delayed snow and glacier melt as well as from groundwater baseflow. Storage and release processes are key to understanding and estimating future changes from headwaters to larger river basins, but they are challenging to model. They are also one of the reasons that trend analyses carried out for multiple streamflow records at continental scales show considerable diversity in the change signals - more diverse than models suggest. In a central European climate, the role of cross-seasonal catchment storage matters not only in regulated river systems but also in regions where expected precipitation changes diverge seasonally. Germany is such a region with expected wetter climate in winter and drier climate in summer. The talk reports on ongoing empirical and model-based research on the streamflow vulnerability to drought given different storage characteristics. To illustrate the importance of the challenge to improve the understanding and prediction of hydrological droughts, the presentation also reports on inter- and transdisciplinary research that draws on textual drought impact reports. These were were systematically collected and coded as an alternative data source to analyse sectorial drought vulnerability. In particular the recent droughts of 2003, 2015 and now 2018 have revealed numerous impacts not only on agriculture but also on river ecology and aquacultures, drinking water supply, navigation, energy, among others. Understanding and predicting such impacts will be key to better drought risk management.

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