Surface water floods in Switzerland: what insurance claim records tell us about the caused damages in space and time

Abstract

Abstract. Surface water floods (SWFs) have received increasing attention in the recent years. Nevertheless, we still know relatively little about where, when and why such floods occur and cause damages, largely owed to a lack of data, but to some degree also because of terminological ambiguities. Therefore, in a preparatory step, we summarize related terms and identify the need for unequivocal terminology across disciplines and international boundaries in order to bring the science together. Thereafter, we introduce a large (n = 63'117), long (10–33 years) and representative (48 % of all Swiss buildings covered) data set of spatially explicit Swiss insurance flood claims. Based on registered flood damages to buildings, the main aims of this study are twofold: First, we introduce a methodology to differentiate damages caused by SWFs and fluvial floods based on the geographical location of each damaged object in relation to flood hazard maps and the hydrological network. Second, we analyze the data with respect to their spatial and temporal distributions aimed at quantitatively answering the fundamental questions of how relevant SWF damages really are, as well as where and when they occur in space and time. This study reveals that SWFs are responsible for at least 45 % of all flood damages to buildings and 23 % of the associated direct tangible losses, whereas lower losses per claim are responsible for the lower loss share. The Swiss lowlands are affected more heavily by SWFs than the alpine regions. At the same time, the results show that the damages are not evenly distributed within each region either. By far the most SWF damages occur during summer in almost all regions. The normalized damages of all regions show no significant upward trend of SWF damages between 1993–2013. We conclude that SWFs are in fact a highly relevant process in Switzerland that should receive similar attention like fluvial flood hazards. Moreover, as SWF damages almost always coincide with fluvial flood damages, we suggest to consider SWFs, just as fluvial floods, as integrated processes of our catchments.

Changes in flood damage with global warming in the east coast of Spain

“…A large number of floods affecting the western Mediterranean region are surface water floods (Llasat et al, 2014;. This type of flood can be regarded as coming under the most general definition of rainfall-related floods (Bernet et al, 2017;. For this reason, precipitation is the main hazard driver of the damage caused by these events.…”