Abstract
Hydrometeorological compound events cause severe economical, societal and environmental damage, but their investigation is difficult as they occur rarely and are multivariate. Here we use 50 high-resolution climate simulations from the single model initial condition large ensemble CRCM5-LE to examine two such compound event types in southern Norway: (1) Heavy rainfall on saturated soil during the summer months (June, July, August, September; SES) and (2) Concurrent heavy rainfall and snowmelt (rain-on-snow; ROS). We compare present-day conditions (1980–2009) with future conditions under a high-emission scenario (2070–2099) and investigate the impact of climate change on the frequency and spatial distribution of SES and ROS events. We find that the probability of occurrence of SES events during the summer increases by 38% until 2070–2099 over the whole study area. The areas with the highest occurrence probability extend from the west coast into the interior. In contrast, the frequency of ROS is projected to decrease by 48% on average, largely driven by decreases in snowfall. Moreover, the spatial pattern of ROS are projected to change, with the most frequently affected areas shifting from the west coast towards the inner country. Our study highlights the benefits of single model large ensemble simulations for the analysis of compound events.
Highlights
A recent study of Berghuijs et al (2019) has shown that most annual maximum floods in Europe are not caused by the highest annual rainfall peaks, but by the co-occurrence of rainfall and snowmelt or rainfall on saturated soil
The occurrence probability of heavy rainfall events on very moist soil increases by 38% from 1980 to 2009 to 2070–2099, whereas the frequency of ROS events decreases by 48% for the whole study area in a high emission scenario (RCP 8.5)
Applying a regional climate model large ensemble with 0.11 resolution enables the representation of topographical features and investigation of meteorological processes at finer spatial scales than are typically avail able in global climate models
Summary
A recent study of Berghuijs et al (2019) has shown that most annual maximum floods in Europe are not caused by the highest annual rainfall peaks, but by the co-occurrence of rainfall and snowmelt or rainfall on saturated soil. Concurrent heavy rainfall and snowmelt can lead to several types of mass movements such as landslides, debris flow or slush flow This type of event is often referred to as rain-on-snow (ROS) event. ROS events are a relatively rare phenomenon They are often the main flood generating process in high latitudes (Cohen et al, 2015) and mountainous areas (McCabe et al, 2007; Merz and Blo€schl, 2003). In Norway, ROS events typically occur during spring when the snow masses accumulated during the winter have not melted yet but temperature starts to rise (Benestad and Haugen, 2007; Pall et al, 2019)
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