Near future changes to rain-on-snow events in Norway

Abstract

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.