How montane forests shape snow cover dynamics across the central European Alps

Abstract. A substantial fraction of seasonal snow is stored in mid-latitude montane forests, serving as an essential temporal water storage. Across vast areas, snow cover dynamics are the result of processes equally controlled by forest structure, topography, climate, and weather variability. As data availability has limited our ability to disentangle how these four key controls interact across landscapes within complex topography, most forest snow studies have focused on only one or two of the controls. In this study, we employed the process-based FSM2oshd forest snow model framework for an in-depth analysis of the current state of forest snow water resources across the central European Alps. Over the 8 years analysed, forest snow accounted for 20–30 % of the total snow storage in midwinter. In the various effects of existing forest cover on snow, pronounced differences were found depending on elevation, aspect, region, and year. While the presence of forest usually led to a decrease in peak SWE, it decelerated snowmelt, often leading to a later snow disappearance date, particularly on south-facing slopes. However, variability between years and regions was strong enough to shift or even reverse such trends, where snow-scarce years accentuated relative differences in the effects of forests on snow cover. With forest disturbances projected to increase and snow storage to further decline, enhanced complexity of snow cover dynamics in montane forests is to be expected. This places more emphasis on understanding how the effects of key controls such as forest structure, topography, and weather interact.