Mapping the city-scale supply and demand of ecosystem flood regulation services—A case study in Shanghai

In the context of climate change and rapid urbanization, pluvial flooding has posed an increasing challenge for urban sustainability and drawn research attention to better understanding the role of an ecosystem's flood regulation service (EFRS) in mitigating floods. However, relatively little is known about the supply and demand of the EFRS at the city scale and about the effect of nature-based solutions on the EFRS. To fill this gap, we present an integrated method to calculate the EFRS supply as the difference between precipitation and runoff using hydrology models and the EFRS demand as the expected flood damages through flood risk analysis. The spatial relationship between the supply and demand of the EFRS is analyzed using spatial statistics. A case study in central Shanghai, China, shows that the total EFRS demand is US$ 1.14 billion for a 100-year pluvial flood, with the demand density decreasing from the west to the east. The total EFRS supply is 2.14 × 10⁷ m³, with the supply density increasing from the center and to the periphery. The EFRS supply and demand are imbalanced, as the demand is relatively higher than the supply in 92 (or 32.86%) catchments. Three of these imbalanced catchments can potentially be satisfied through inter-catchment EFRS sharing from neighboring catchments with abundant supplies of the EFRS. The number of imbalanced catchments can also be reduced to 27–42 by adopting concave green lands. The proposed methods have a broad application in other cities around the world. These findings could facilitate a comprehensive understanding of the EFRS at the city scale and help policy-makers formulate an integrated flood risk management strategy.