Assessment of Climate Change Impacts on Flood Event Types in Two Alpine Catchments

Abstract:

A variety of different climate factors can trigger floods: intense rainfall, long lasting rainfall or extreme amount of snowmelt. As a result, changes in climate extremes can affect both the frequency of floods, but also other factors such as seasonality and duration, all of which have implications on local social and ecological systems. Therefore, we present a technique for examining projected changes in flood events types, focusing on antecedent meteorological conditions. Floods (characterized by the historical 10 and 25-year return level discharge) are clustered into causal types based on rainfall, antecedent precipitation and temperature. A multi-site weather generator coupled with a conceptual rainfall-runoff model is employed to increase the number of flood events. Quantile mapping of precipitation and temperature projections is then used in the development of future discharge. The technique is applied to two different catchments in the European Alps: a smaller catchment in the southern French Alps, dominated by rain-on-snow floods, and a larger catchment in Austria, with more floods during summer. The results show that changes in precipitation and temperature can alter not only the frequency, but also the distribution of flood event types in the future. Furthermore, assessing changes in flood event types provides information about why the frequency of floods in an alpine catchment may change, even if the projections themselves are highly uncertain.