Response of Surface Water Quality in Urban and Non-urban Areas to Heavy Rainfall: Implications for the Impacts of Climate Change

Abstract

Frequency and severity of floods and droughts are increased across the world due to global climate change. However, the responses of water quality in urban and non-urban areas to extreme weather events are not well understood. The heavy and extensive precipitation during the summer of 2011 and 2012 caused two severe floods in Beijing of China. This work evaluated the impacts of these two floods on the water quality of 10 urban lakes, 3 non-urban reservoirs, and 8 non-urban rivers through comparing the pre-flood and post-flood water quality as well as those in reference period (2006-2010). Results indicated that the lagging response of water quality to flood is more significant in non-urban areas than the urban areas. In addition, comprehensive pollutant index (CPI) during the first flood period in most sites were much higher than the reference values with the average increasing rate of 46%. The values of chemical and biological oxygen demand were elevated in most sites; total nitrogen in the non-urban areas and total phosphorous in the urban areas were higher than those in the reference period. The different responses of nitrogen and phosphorus to the flood events of the two areas were mainly due to the high nitrogen contents in non-urban soils and high phosphorus contents in the urban soils. While most pollutant concentrations during the second flood period were lower than the first flood period, or even lower than the reference period. This was because the first flood, belonging to the post-drought flood, scoured the land surface and brought plenty of pollutants into the aquatic environments; while the non-point source pollution caused by the second flood was less effective and mainly reflected as dilution effect. This study suggests that the response of surface water quality to floods caused by climate change will differ between urban and non-urban areas, as well as among different flood events.

Keywords: heavy rainfall, water quality, urban area, non-urban area, flood risk management