Linking trends in urban extreme rainfall to urban flooding in China

Storm-induced urban flooding is a global issue that causes large damages and fatalities. Characterizing extreme rainfall is critical to urban flood risk management. Although China's cities have been experiencing a rapid increase in urban flooding in recent decades, there is a lack of national-wide analysis of the occurrence of extreme urban rainfall. This study examined the trends in extreme rainfall in 146 cities in China for the period 1960-2014. The trends were also analysed in terms of city size (small, big and mega cities) in two city clusters (Jing-Jin-Jin City Cluster and Yangtze City Cluster). There was a strong spatial variation in the trends of extreme rainfall across the country, with negative trends in North China and positive trends in Southeast China. Both positive and negative trends were noted for the other regions of China. All the cities in Jing-Jin-Ji City Cluster had a decreasing trend in extreme rainfall, with a significant decline (p = 0.03) for mega cities. Then all cities in the Yangtze City Cluster had an increasing trend in extreme rainfall, with a significant increase (p=0.02) for big cities. The findings suggested that efforts to alleviate storm-induced urban flash floods should take into account both spatial disparities in climate and future changes in extreme rainfall events.