Simulation of the radiative effect of haze on urban hydrological cycle using reanalysis data in Beijing

Abstract. Although, air pollution modifies local air temperatures and boundary layer structure in urban areas, little is known about its effects on the urban hydrological cycle. To explore this, changes in the urban surface water balance during different haze levels are modelled in Beijing using the Surface Urban Energy and Water Balance Scheme (SUEWS), forced by reanalysis data. The pollution levels are classified using aerosol optical depth observations. We show how the reanalysis radiation data do not include the attenuating effect of haze and develop a haze correction for the incoming solar radiation. With this haze correction the SUEWS model simulates the eddy covariance measured latent heat flux well. Both surface runoff and drainage increase with severe haze levels particularly with low precipitation rates: runoff from 0.06 to 0.18 mm day −1 and drainage from 0.43 to 0.62 mm day −1 during fairly clean and extremely polluted conditions, respectively. When all precipitation events are taken into account, runoff is higher during the extremely polluted conditions than with cleaner conditions except during the cleanest conditions when the high precipitation rates induces largest runoff. Thus, haze is not likely impacting on the likelihood of flash floods. However, the low runoff rates commonly transport pollutants to soil and water and therefore their changes are important to understanding detailed deterioration of urban soil and aquatic environments.