Urbanization Impacts on the Summer Heavy Rainfall Climatology over the Eastern United States

Abstract

he relationship between rainfall characteristics and urbanization over the Eastern US was examined by analyzing four datasets: daily rainfall in 4,593 surface stations over the last 50 years (1958-2008), a high resolution gridded rainfall product, reanalysis wind data, and a proxy for urban land-use: gridded human population data. Results indicate that summer monthly rainfall amounts show an increasing trend in urbanized regions. The frequency of heavy rainfall events has a potential positive bias toward urbanized regions. Most notably, consistent with case studies for individual cities, the climatology of rainfall amounts downwind of urban-rural boundaries shows a significant increasing trend. Analysis of heavy (90th percentile) and extreme (99.5th percentile) rainfall events indicated decreasing trends of heavy rainfall events and a possible increasing trend for extreme rainfall event frequency over urban areas. Results indicate that the urbanization impact was more pronounced in the Northeast and the Midwestern US with an increase in rainfall amounts. In contrast, the southeastern US showed a slight decrease in rainfall amounts and heavy rainfall event frequencies. Results suggest that the urbanization signature is becoming detectable in rainfall climatology as an anthropogenic influence affecting regional precipitation; however, extracting this signature is not straightforward and requires eliminating other dynamical confounding feedbacks.