xWEI – A novel cross-scale index for extreme precipitation events

How can the extremity of an rainfall event be quantified? Extreme rainfall events are rarely homogeneous regarding rainfall intensities and the spatio-temporal distribution of rainfall can cause flooding on different scales. While small, mountainous catchments can react to short but high-intensity precipitation with flash floods, the same event can also trigger pluvial or fluvial floods on a spatially bigger scale with lower intensity precipitation, leading to compound flood events. Consequently, these cross-scale characteristics of extreme rainfall events are an important factor that should be considered regarding hydrological response or disaster management.

To quantify the extremity of rainfall events while considering the spatial and temporal distribution of rainfall, we introduce a new index, xWEI, based on the Weather Extremity Index (WEI). By using precipitation radar data with a high spatial and temporal resolution, we analyzed and evaluated extreme rainfall events in Germany and were able to show essential differences in the performance of the classical approach (WEI) and xWEI. 

This novel cross-scale index, in combination with modern high-resolution precipitation radar data, enables a better identification of extreme events and their characteristics and helps to link them to their impacts.