Determining Hydrological Controls on Flood Frequency
Flooding is a major natural hazard with significant societal, economic, hydrological, and ecological consequences. To improve flood frequency estimates, a recent study, led by U.S. Department of Energy scientists at Pacific Northwest National Laboratory, provides insights on the connections between flood frequency and the annual water balance. Researchers performed the study using data from several hundred catchments across the continental United States. The research expressed mean annual water balance in terms of two controlling measures: (1) the climatic aridity index (AI), which is a measure of the competition between evaporation and precipitation, and (2) the base flow index (BFI), which is a measure of total runoff partitioning into surface and subsurface components at the annual time scale. Their results showed that the AI has a first-order control on the shape of the flood frequency curve in terms of the mean and variability of the annual maximum floods. While the mean annual flood discharge decreases with increasing aridity, variability increases. In contrast, the BFI was found to exert a second-order control on the flood frequency. Higher BFI, meaning higher contributions of subsurface flow to total streamflow, leads to a decrease of the mean annual (specific) flood discharge, and vice versa. By attributing regional variations of the flood frequency curve to AI and BFI, this study provided the basis to delineate hydrological regions using the two indices for flood frequency regionalization, which may help improve flood estimation and prediction.
Guo, J., H. Li, L. R. Leung, S. Guo, P. Liu, and M. Sivapalan. 2013. “Links Between Flood Frequency and Annual Water Balance Behaviors: A Basis for Similarity and Regionalization,” Water Resources Research, DOI: 10.1002/2013WR014374.