Quantifying the impact of latent heat on urban climate: a perspective from a novel parameterization scheme

Urban latent heat processes are neglected or oversimplified in most mesoscale models in previous studies, leading to large uncertainties in modelling urban climate. By coupling our newly developed urban hydrological parameterization scheme in the mesoscale model WRF/BEP+BEM, we conducted three one-month simulation tests to quantify the impact of latent heat processes on urban climate, which is induced by urban ground greening, green roofs and surface water. It is found that urban latent heat significantly reduces maximum temperatures and improves comfort, especially during heatwaves, but it does not markedly influence mean air temperature. Compared to ground greening, green roofs provide enhanced cooling advantages. Overall, all three latent heat processes produce a more spatially dispersed distribution of precipitation with a reduction of 25% in total precipitation amount. This can be attributed to the reduced urban heat island intensity by latent heat and the enhanced stability of the planetary boundary layer. The finding has implication for the measures that can be taken in reducing the adverse impact induced by rapid urban expansion.