Modeling the heat transfer of rainfall runoff in the typical catchment of Beijing

Abstract

The stormwater runoff formed on the urban impervious surface in summer may carry a large amount of heat, which will have a negative impact on the urban receiving water bodies. In order to simulate the process of runoff generation, confluence, and heat transfer, evaluate the degree of thermal pollution of stormwater runoff, and better quantify the heat of stormwater runoff, a simplified urban stormwater runoff temperature model is developed according to the runoff process of pervious surface and impervious surface and pipe network during rainfall, combined with the heat transfer principle in the process, to calculate the runoff flow and temperature from the small catchment. The heat transfer model mainly considers the heat exchange between runoff and surface, runoff and atmosphere, and runoff and pipe. The proposed model was evaluated by monitoring of typical urban catchment in the summer of 2021–2022, and the calculation formula of Event Mean Temperatures (EMT) in the catchment was proposed based on the model principle. The average root mean square error (RMSE) between the predicted value and the monitoring value of the model is 0.6 ℃. Long duration rainfall and short duration high intensity rainfall could lead to large simulation errors. Runoff temperature is easily affected by air temperature, solar radiation, pre-rain temperature and type of impervious surface. The average error between the EMT calculated by the formula and the actual monitoring EMT is 0.6 ℃, and its significant error rainfall frequency is consistent with the model. The results show that the model and formula can be used to predict the runoff heat in typical catchments, providing a more convenient method for the analysis of runoff heat in small catchments.