Evaluating the impact of urban development on flood risk

According to a new study, urban development may cause severe issues when it comes to flooding risk.

The study, recently published in Geophysical Research Letters, was conducted by scientists from the Johns Hopkins University and the United States Geological Survey (USGS). It suggests that for 1% impervious pavement development (e.g. roads and parking lots), the average flood incidents per year will rise by 3.3%.

The impact of urban development on the potential flood flows has been studied before but, most attempts focus on a small amount of data and could not derive an actual correlation between the 2. Other parameters such as the climate, the usage of land or the existence of nearby dams affect the results, therefore, a single case study is not suitable for determining an actual correlation.

Nevertheless, researchers managed to address this issue and assess the impact of impervious surfaces on the rate of flooding increase. For this purpose, they gathered and analyzed data from 1974 to 2012 that included water flowing information of more than 2,100 streamgaging stations provided by the USGS. Then, they evaluated the urban growth of the basins located upstream of the stations. "Due to the large variability in annual flooding, it is difficult to isolate the effect of urbanization. Combining these large datasets with both time and space dimensions allowed us to tease out and calculate the magnitude of the effect," Dr. Annalise Blum, lead-author of the study and a postdoctoral fellow at the Department of Earth and Planetary Sciences, Johns Hopkins University, said.

The team incorporated complex mathematical models to analyze the data and derive reliable results that have not been widely used in the study of flood flows. According to Dr. Paul J. Ferraro, co-author of the study and a Bloomberg Distinguished Professor of Human Behavior and Public Policy at Johns Hopkins University, deriving the most suitable model to determine the cause and effect correlation is of great importance. "...in the last few decades, fields like economics and biostatistics have made great advances in methods that can isolate cause and effect. By bringing these methods to hydrology, we hope that we can spur advances in hydrological science, as well as in the urban policies and programs that depend on that science," Prof. Ferraro, stated.

Researchers aim at applying their method in future urban development planning. Acknowledging the large impact of impervious surfaces on flooding may be an inhibitory factor towards improvident urban development or, at least, it could drive designers to search for more intelligent solutions. For example, according to the results of the study, if an intact river basin is urbanized and impervious surfaces reach 20% of the total area, the annual flooding will experience a 66% increase.

Source: Johns Hopkins University