The effects of river regulation on global river flood risk assessments

Abstract

Due to large worldwide economic losses due to flooding, the large size of watersheds and the lack of data in developing countries global river flood risk assessments are developed to be able to estimate the potential economic risk of floods. The potential impacts of these assessments are based on Global Hydrological Models (GHMs), which are being used in studies related to land surface hydrology. In this study the GHM PCRaster GLOBal Water Balance model (PCR-GLOBWB) is used. However, river regulation (dikes and floodways) is not yet explicitly included in the model. As a case the Mississippi watershed is used to analyze the impact of including dike heights from the National Levee Database of the U.S. Army Corps of Engineers by pre-processing the channel dimensions and therewith the channel capacity. The response of the model to the changes in channel capacity due to increasing dike heights and the inclusion of floodplains and the response to floodways is analyzed during this study. Two different methods are used to translate the flood outcomes of the PCR-GLOBWB model to economic damage. The urban damage method is based on a depth-damage relationship, which is applied on a total GDP distribution based on nightlight intensity. The agricultural damage method is based on a duration-damage relationship that is applied on the most common crop, soybeans. Based on the average price per bushel, bushel per ha, vegetation fraction and month of flooding the economic damage is determined. Simulated economic damages are validated by comparing it with observed damage from the international disaster database, EM-DAT.

Overall, it can be concluded that the impact of including river regulation on extreme river discharges is small, when considering an increasing Manning coefficient. However, the impact on flooding is large and therewith it has a considerable impact on resulting damages.