Peak precipitation intensity in relation to atmospheric conditions and large-scale forcing at midlatitudes

Abstract

Research on relations between atmospheric conditions and extreme precipitation is important to understand and model present-day climate extremes and assess how precipitation extremes might evolve in a future climate. Here we present a statistical analysis of the relation between large-scale conditions and hourly precipitation at midlatitudes, by using observations of the Netherlands combined with a regional reanalysis. The aim is to gain a better understanding of the typical large-scale atmospheric conditions and large-scale forcing associated with extreme hourly precipitation and determine the typical differences between cases of extreme precipitation and weaker events. To avoid double counting, we perform an event-based analysis and consider the hourly peak intensity, rather than all hourly data. Atmospheric large-scale profiles consistently show a clear separation between precipitation deciles, characterized by increasing instability and moisture content of the atmosphere for more extreme precipitation. Furthermore, stronger events are characterized by larger atmospheric forcing preceding the event, which primarily relates to vertical motions. Based on these results, four atmospheric parameters, describing atmospheric moisture, stability and large-scale convergence, are analyzed as potential indicators of strong precipitation events. Despite positive relations between these parameters and the peak intensity, their correlations are found to be weak.