# Investigation of Rain-On-Snow Floods under Climate Change
## 1 Introduction  
Floods that are caused by the so-called rain-on-snow (ROS) events can lead to major economic loss, can endanger human lives and require efficient water management. The combined effect of snowmelt and rainfall can lead to higher flood magnitudes compared to only snowmelt or rain-induced floods. More specifically, in case of a ROS event moderate rainfall amounts can lead to significant runoff because during a rainfall event latent heat input and long wave radiation can speed up snowmelt, or antecedent snowmelt can lead to saturation of large areas, which increases runoff [1]. This means that ROS events can be classified as compound events. Additionally, climate change is expected to impact various hydro-meteorological variables and processes such as air temperature or temporal and spatial rainfall distribution. These changes can also affect the runoff regime, flood characteristics, and water management policies. However, it is still not clear how will climate-change-induced alterations influence ROS events due to their compound nature.  
It can be expected that the runoff regime will have a different dynamics that could lead to more frequent and extreme flood events due to climate change. Numerous studies have been carried out to assess the possible impact of climate change on the hydrological regime [2]. In [3], it was statedthat global flood risk could rise by 187% due to the climate change impact compared to the situation without climate change. ROS floods' frequency could increase in the future due to the ascending trend in air temperature and the changed rainfall regime. In this regard, flood risk changes have been examined by taking into consideration climate change scenarios in various parts of the world (e.g., [4; 5; 6; 7]). Future shifts in extreme flow regimes in Alpine regions were investigated by [8], where the results show that changes in extreme high-flow regimes for rainfall-dominated regions are different than those in melt-dominated regions. They reported an increase in the maximum discharge in rainfall-dominated regions in the future, whereas in melt-dominated regions the situation could be opposite. The effects of climate change on climate variables such as precipitation, snowfall, and air temperature, and hazards such as floods and droughts were investigated by [5] in the Alps in Europe. They found that the increasing trend in air temperature could lead to significant decreases in the snow amount and, given the climate projections for the 21 st century, an increase in the frequency of natural hazards such as floods. In [9], the ROS floods in the Sitter basin in Switzerland were examined. The results revealed that the number of ROS events could increase due to the increase in air temperature by about 2-4 \({}^{\circ}\)C. In this regard, they stated that ROS events could cause severe floods in the future. In the study by [10], the hydrological variables were simulated using regional climate models (RCMs) and the influence of bias correction on the future (2071-2100) projection of hydrological extreme events over Europe was investigated. The authors found that the flood occurrence interval in most European rivers would decrease, whereas it would increase in the northeast part because of the warmer winter and shorter snow period.  
Because an increase in the number of extreme flood events has been observed over the last decades in Slovenia [11], while climate change projections predict an increase in the air temperature for all future periods in Slovenia [12], we could expect also changes in the occurrence of ROS events. Therefore, the main aim of this study was to investigate the climate change impact on the frequency, magnitude, and seasonality of ROS floods in the selected catchments located in various climate regions in Slovenia.