The possible influence of urban surfaces on rainfall development: a sensitivity study in 2D in the meso-γ-scale

Urban areas can represent a considerable part of the model domain in meso-scale numerical simulations with typical horizontal domain lengths of 20–200 km. This paper addresses the question of the extent of the influence of urban surfaces on the development of convective precipitation in meso-γ-scale numerical models. For this purpose, a spatially variable parameterization scheme for surface sensible heat flux, surface latent heat flux, and roughness is introduced into a meso-scale numerical model. A sensitivity study in 2D is performed to assess the impact of variations of the individual parameters on the development of precipitation. The results indicate that surface conditions should not be neglected and can have considerable influence on convective rainfall. It appears that within a time frame of 4 h it is particularly the sensible heat flux variations that have the most significant impact.