Flooding is becoming more frequent in the central United States, however there is little evidence that the severity of these floods has changed, reports a paper published online in Nature Climate Change. This change in frequency is attributed to shifts in seasonal rainfall patterns and increases in temperatures.
Using observational records from 774 stream flow measurement stations, Iman Mallakpour and Gabriele Villarini investigated how flood events across the central United States have changed from 1962 to 2011.
The authors found that the frequency of floods has increased across large areas, from North and South Dakota in the west to Iowa, Illinois and Ohio in the east, whilst there have been decreases in flooding frequency in the northeast and southwest central United States. These changes are in line with rainfall trends, with the exception of Kansas and Nebraska where, despite rainfall increases, floods have decreased due to pond construction and replenishment of depleted groundwater.
The authors also investigated the discrepancy between the frequency of floods being highest in the spring and summer months, despite peak rainfall occurring in the summer. For the northern region of the study area, they suggest that the spring increase is due to higher temperatures causing more snow to melt, resulting in the largest increase in flooding frequency.