Modeling snow redistribution by wind and avalanches in hydrological studies in alpine catchments is important, as the spatial variability of the snow cover has an impact on timing and magnitude of the snowmelt runoff. Disregarding snow redistribution in models can lead to the formation of ‘snow towers,’ i.e., multi‐year accumulation of snow at high elevations and an incorrect water balance. The reviewed approaches to deal with snow redistribution in hydrological models were first broadly grouped by the represented physical processes: (1) the correction of the precipitation input data to account mainly for preferential deposition, (2) the description of all wind‐driven processes based on wind field data, (3) the description of gravitational transports and/or wind‐driven processes based on topographic information, and (4) the statistical description of the variability of the snow water equivalent (SWE) to account for all types of snow redistribution. The review further assessed the implementation of these approaches in physically based and bucket‐type hydrological models. Generally, snow redistribution consideration has improved the simulation of snow patterns and SWE and consequently the prediction of discharge in mountain catchments worldwide. Snow redistribution approaches still have some limitations and a large gap exists between the knowledge and processes in highly detailed physically based snow models and the widely used bucket‐type hydrological models used for water resources and climate change studies. There is a real need to bridge this gap using the knowledge earned by snow redistribution modeling with established physically based models to develop more conceptual approaches for the application in bucket‐type models. WIREs Water 2017, 4:e1232. doi: 10.1002/wat2.1232This article is categorized under: Science of Water > Hydrological Processes Science of Water > Methods Science of Water > Water and Environmental Change

Abstract. In January 2011 a rain-on-snow (RoS) event caused floods in the major river basins in central Europe, i.e. the Rhine, Danube, Weser, Elbe, Oder, and Ems. This event prompted the questions of how to define a RoS event and whether those events have become more frequent. Based on the flood of January 2011 and on other known events of the past, threshold values for potentially flood-generating RoS events were determined. Consequently events with rainfall of at least 3 mm on a snowpack of at least 10 mm snow water equivalent (SWE) and for which the sum of rainfall and snowmelt contains a minimum of 20 % snowmelt were analysed. RoS events were estimated for the time period 1950-2011 and for the entire study area based on a temperature index snow model driven with a European-scale gridded data set of daily climate (E-OBS data). Frequencies and magnitudes of the modelled events differ depending on the elevation range. When distinguishing alpine, upland, and lowland basins, we found that upland basins are most influenced by RoS events. Overall, the frequency of rainfall increased during winter, while the frequency of snowfall decreased during spring. A decrease in the frequency of RoS events from April to May has been observed in all upland basins since 1990. In contrast, the results suggest an increasing trend in the magnitude and frequency of RoS days in January and February for most of the lowland and upland basins. These results suggest that the flood hazard from RoS events in the early winter season has increased in the medium-elevation mountain ranges of central Europe, especially in the Rhine, Weser, and Elbe river basins.

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