Statistically-based projected changes in the frequency of flood events across the US Midwest

There is growing empirical evidence that many river basins across the U.S. Midwest have been experiencing an increase in the frequency of flood events over the most recent decades. Albeit these detected changes are important to understand what happened in our recent past, they cannot be directly extrapolated to obtain information about possible future changes in the frequency of flood events. Building on recent statistically-based attribution studies, we project seasonal changes in the frequency of flood events at 286 U.S. Geological Survey gauging stations across the U.S. Midwest using projections of precipitation, antecedent wetness conditions and temperature as drivers. The projections of the covariates are obtained from two datasets obtained by down-scaling global circulation models from the Fifth Coupled Model Intercomparison Project (CMIP5). We focus on the representative concentration pathway (RCP) 8.5 and on four different flood thresholds (i.e., from more common to less frequent flood events). We find that the frequency of flood events during the 21st century increases during spring at most of the analyzed gauging stations, with larger changes in the Northern Great Plains and regardless of the flood threshold value. Our findings also point to a projected increasing number of flood events during the winter, especially in the stations in the southern and western part of the domain (Iowa, Missouri, Illinois, Ohio, Indiana and Michigan). A marked change in the frequency of flood events is not projected for the summer and fall.