Investigating the relationship between circulation patterns and cloudburst character in a changing climate

Sammanfattning: The consequences of extreme weather in terms of heavy precipitation and flooding are devastating in both rural and urban areas. The cost on society to handle the damages are substantial. It is therefore of high interest to further investigate the mechanisms behind these extreme events. With a better understanding and future forecasting of heavy precipitation events (cloudbursts), the urban areas can adapt their infrastructure to future demands which would make the cities less vulnerable to flooding. To better understand the mechanisms behind extreme precipitation scientists have studied North Atlantic atmospheric circulations and found a relation between those atmospheric circulations and cloudbursts in northern Europe. Furthermore, earlier studies have shown an indication of more frequent atmospheric circulation that causes cloudbursts in northern Europe in the future. Wei Yang at Swedish Meteorological and Hydrological Insti- tute (SMHI) defined twelve new circulation pattern classes of North Atlantic scale, and this study aimed to investigate if there is a relation between those classes of circulation patterns and five empirical hyetographs generated by Olsson et al. (2017). This was ac- complished by investigating what circulation pattern was present the day the cloudburst occurred. If a relation was found, the second objective was to see how the future fre- quencies of the circulation patterns would affect the distribution of hyetograph shape. To investigate future frequencies of the circulation patterns results from climate models were used. The result showed an indication of a relation between circulation patterns and cloudburst character. The number of events was too small for any robust conclusions to be made, but tendencies were found, and further investigation could show more interesting results. Based on the assumption that the frequency of cloudbursts for each circulation pattern would stay the same in the future, the result in this study showed that the distribution of hyetograph shape would not change considerably in the future.