Spatiotemporal Shift and Heterogeneity of Rain-on-Snow Events

The rapid snowmelt that typically occurs after snow accumulates at low temperatures and precipitation develops at higher temperatures is a defining characteristic of rain-on-snow (ROS). In ROS events, the significance lies not only in the spatial variability of snow coverage but also in factors like snow depth, variations in rainfall over time and space, rates of snowmelt, topographic conditions, saturation of soil moisture, vegetation, and surface roughness. During ROS events, the swift release of melted snow water can result in flash floods and a substantial surge in runoff, which in turn can lead to the overflow or elevation of rivers and consequently severe inundation and flooding. This study reveals the climatology of ROS events and examines the connections between ROS events and surface runoff quantities, aiming to contribute to flood projections and snow research for Türkiye, specifically focusing on the regions in the north and east of the country that receive substantial snowfall and have previously encountered serious flooding. The findings indicate a decline in ROS events in the Eastern and Southeastern Anatolia regions, particularly throughout the past three decades, while there has been an increase in the Central and Western Black Sea regions. The decline in the quantity of ROS (rainfall over snow) in the Southeastern Anatolia region, which serves as the primary water source for Turkey, is a favorable outcome as it leads to a decrease in the risk of floods, a longer duration of snow cover, and the feeding of water resources. Given the rise in ROS events in the Central and Western Black Sea regions, it is imperative to formulate novel urbanization strategies to mitigate potential flood risks and minimize associated damages that consider the region’s topography, urbanization, and precipitation patterns. In addition, the results reveal a startling new trend: ROS events are shifting both spatially and temporally.