Emission of greenhouse gas from urban polluted river during different rainfall events: Typhoon and storm will promote stronger evasions

Urban rivers have been recognized as significant hotspots for greenhouse gas (GHG) emissions. However, the impact of storms or typhoons on GHG emissions from urban rivers is not well understood. Suzhou Creek located in the highly developed urban area of Shanghai was selected to investigate of changes in CO2, CH4, and N2O concentrations and diffusive fluxes during different rainfall events from May to October 2021. The findings showed that urban rivers were sources of GHG emissions during various events. The average diffusive fluxes of CO2, CH4, and N2O during typhoon events were 1 to 2 orders of magnitude higher than those during non-typhoon period, revealing that typhoon greatly promote GHG evasion. GHG CO2-equivalents were ranked as follows: during typhoon (3.93 g m(-2)h(-1)) > post-typhoon (0.89 g m(-2)h(- 1)) > high precipitation (0.33 g m(-2)h(- 1)) > non-precipitation (0.29 g m(-2)h(- 1)) > small precipitation (0.25 g m(-2)h(- 1)). Rainfall dilution, pump station drainage, sediment disturbance, and a high gas transfer coefficient induced by typhoons were the main factors affecting GHG emissions. Nutrients, chlorophyll-a, and dissolved oxygen in river water were important control parameters for GHG production. Overall, typhoon would release large amounts of GHG from urban rivers. Given the projected increase in the frequency and complexity of extreme weather events, this study highlights the importance of better understanding the dynamic response of urban river GHG to rainfall and typhoons.