Analysis of temperature characteristics and influencing factors of the stormwater runoff in typical catchment in Beijing

With the development of urbanization, the rate of impervious surface area has increased greatly, and a series of problems have attracted more and more attention. The risk of adverse impacts on the water ecology and water environment has become more and more prominent in the summer when the surface of the urban catchment produces high temperature runoff and then sinks into the downstream receiving water bodies caused by the thermal pollution of stormwater runoff. A typical catchment in Beijing was selected to monitor and analyze the runoff temperature of several rainfall events from 2021 to 2022. The data of meteorological factors, underlying surface temperature and pipeline runoff heat were collected simultaneously, and the Pearson correlation coefficient method was applied to analyze the influencing factors. The results showed that the temperature of stormwater runoff often increased in summer rainfall in the study area, and rainfall events with precipitation less than 12.5 mm and durations shorter than 250 min were more prone to warming, with a maximum warming of 4.1 ℃. Runoff temperature increases tended to occur at the beginning of the runoff process, with an average time to peak of 38 min, and there was no obvious relationship between the temperature rise and the peak location of rainfall intensity. The highly significant (P<0.01) influencing factors of stormwater runoff temperature included air temperature, precipitation, rainfall duration, and the impervious surface temperature at the initial moment of rainfall. The four indicators of air temperature during rainfall, rainfall duration, impervious surface temperature, and pipe wall temperature at the initial moment could explain 96.7% of the runoff temperature output in the study area.