The changing pattern of urban flooding in Guangzhou, China.

Extensive research has focused on modelling and analysis of urban flooding in relatively small catchments. Findings in small areas tend to be site-specific, and may not be applicable to larger study areas. Larger scale studies can identify general patterns and influential factors; however, few studies have investigated urban flooding on a larger scale such as a metropolitan area. In this study, we explored the spatial-temporal patterns of urban flooding during the period of 2009-2015 in the central area of Guangzhou, China. Under the framework of Pressure (precipitation and impervious surface)-State (urban flooding)-Response (drainage improvement), we evaluated reasons for the State change and effectiveness of the Response. Overall the urban flooding state showed a fluctuating and improving trend. The fluctuation of the flooding state trend is due to precipitation variation, and the improving trend is attributed to drainage improvement. Furthermore, drainage improvement in the upstream area had led to new flooding in the downstream area. It is evident that the mitigation effect of urban flooding in Guangzhou varied significantly across the city. It is further suggested to regularly collect urban flooding records in cities with flood risk, so that more appropriate policies and measures about urban flooding mitigation can be developed.