Rapid urbanization in China is exacerbating the threat of floods in cities. The Pearl River Delta in Guangdong Province, which is one the largest metropolitan regions in the world and home to a population of more than 52 million people, has been experiencing stronger precipitation than surrounding non-urban regions. That's according to a new study funded by the Key Technologies R&D Program in China.

A team of researchers at Sun Yat-sen University report that urban areas are experiencing stronger rainfall and precipitation here is less frequent but more intense. Urban areas are also experiencing more convective rainfall and afternoon precipitation. These observations imply that urbanization-related environmental changes are increasing the frequency of heavy rainfall.

Given the scarcity and uneven distribution of in situ meteorological measurements over the Pearl River Delta, the researchers used satellite rainfall estimates – from the Tropical Rainfall Measuring Mission – for more uniform and continuous data. In addition, the researchers used a new approach that involves analysing strong and weak precipitation separately because the mechanisms behind each are different.

The results provide further evidence that urbanization is impacting on local rainfall. Previous studies reported an increase in precipitation in urban areas and this work is further proof that urbanization results in an increase in strong rainfall and a decrease in weak precipitation.

The significantly increasing trend in the frequency of heavy-rainfall climatology over urban regions in China could seriously affect ecosystems, society and economic activity. It highlights a need for detailed impact studies to evaluate the associated risks and costs, and to develop abatement strategies.

(By Weibiao Li, Environmental Research Web, 26/09/2011)