Rain-on-snow (ROS) events occur primarily in cold climates such as high latitudes and high elevations where they pose a considerable threat to nature and society. The frequency and intensity of ROS events are expected to change in the future, but little is known about how they will change in the near future (mid-century) and their link to hydrological extremes (e.g. 95% high flows). Here we use kilometre-scale regional climate simulations over Norway, a ROS ‘hot spot’, to determine potential changes in ROS frequency and intensity in the middle of the century under RCP8.5. Analysis shows that ROS will intensify in the future and ROS frequency will increase at high elevations and occur less frequently at lower elevations. Furthermore, high-flows that coincide with ROS events are expected to increase in winter and autumn. In general, this study shows that ROS changes in winter and autumn are related to changes in rain while ROS changes in spring and summer are related to changes in the snowpack. Since rainfall in Norway is dominated by large scale processes in autumn and winter (e.g. North Atlantic storm tracks), it is likely that future changes in ROS climatology in autumn and winter are related to changes in the large scale atmospheric system. This contrasts with spring and summer when local-scale processes drive snowmelt and hence future changes to ROS in those seasons.

雪上雨 (ROS) 事件主要发生在高纬度和高海拔等寒冷气候中，对自然和社会构成相当大的威胁。预计 ROS 事件的频率和强度在未来会发生变化，但对于它们在不久的将来（本世纪中叶）将如何变化以及它们与水文极端事件（例如 95% 的高流量）的联系知之甚少。在这里，我们使用挪威这个 ROS“热点”的公里尺度区域气候模拟来确定 RCP8.5 下本世纪中叶 ROS 频率和强度的潜在变化。分析表明，未来ROS会加剧，ROS频率在高海拔地区增加，在低海拔地区出现频率较低。此外，预计与 ROS 事件同时发生的高流量将在冬季和秋季增加。一般来说，本研究表明，冬秋季ROS变化与降雨变化有关，而春夏季ROS变化与积雪变化有关。由于挪威秋季和冬季的降雨以大尺度过程为主（例如北大西洋风暴路径），因此未来秋季和冬季 ROS 气候学的变化很可能与大尺度大气系统的变化有关。这与春季和夏季形成鲜明对比，当时局部规模的过程推动了融雪，从而导致这些季节 ROS 的未来变化。未来秋冬季ROS气候学的变化很可能与大尺度大气系统的变化有关。这与春季和夏季形成鲜明对比，当时局部规模的过程推动了融雪，从而在这些季节推动了 ROS 的未来变化。未来秋冬季ROS气候学的变化很可能与大尺度大气系统的变化有关。这与春季和夏季形成鲜明对比，当时局部规模的过程推动了融雪，从而在这些季节推动了 ROS 的未来变化。