PNNL

Abstract

Mesoscale convective systems (MCSs) that are clustered in time and space may contribute more to severe flooding than non-clustered MCSs. To quantify this contribution, floods in the Storm Event database in April-August of 2007-2017 are matched with clustered MCSs identified from a high-resolution MCS dataset and terrestrial conditions in a land surface dataset. Clustered MCSs preferentially occurring in April-June are more effective in producing floods, which also last longer due to their greater rainfall-per-area, and produce greater runoff-per-area than non-clustered MCSs. While wetter initial soil conditions encountered by an individual MCS favors flooding, they are less important in flood occurrence for MCS clusters because each MCS of a cluster may saturate the soils so repeated MCS passages over the same region can lead to flooding regardless of the initial soil wetness encountered by the cluster. This study underscores the importance to understand clustered MCSs to better understand changing flood risks