Trends in Flood Magnitudes, Flood Extents and Their Drivers

Abstract:

When rivers flood, they often do so simultaneously with surrounding rivers. We call the area across which this happens the flood extent. We study trends in flood extents in Europe and the US, and analyze how they are linked to trends in flood magnitude. For the time period 1960-2010 we analyze the annual maximum floods of ~5000 US- and ~4000 European hydrometric stations and investigate generating processes of all floods based on climate re-analysis data. We use event synchronization and complex networks to find groups of stations that have similar flood behavior. For both regions, we find a positive correlation between extents and magnitudes for 93% of the stations. While the trends of both variables are well aligned in Europe (increasing in the west, decreasing in the south), the same is not true for the US. The station groups help us to understand these differences. We show that the changing influence of snowmelt on flood generation is crucial for the relationship of magnitude and extent trends.