Impact of urban land use on mean and heavy rainfall during the Indian Summer Monsoon

Abstract. Northern India has been subjected to an intense urbanization since the middle of the twentieth century. The impact of such a drastic land-use change on regional weather and climate remains to be assessed. In this work, we study the impact of the modification of land-use – from vegetation to urban – on the Indian summer monsoon rainfall, as well as other meteorological variables. We use the regional meteorology model Meso-NH coupled with an urban module (the Town Energy Balance model) to perform month-long sensitivity simulations centered around Kolkata, the most urbanized area in Northeastern India. Paired simulations, one with and another without urban settings have been performed to identify the impacts related to urbanization through both thermodynamic and kinetic effects. We find that the perturbation induced by urban land-use enhances the mean rainfall over the model domain, principally by intensifying the convective activity through thermodynamical perturbation, leading to an increase of 14.4 % of the monthly mean rainfall. In addition, the modeling results demonstrate that not only does the urban area act in general as a rainfall enhancer, particularly during nighttime, but it also induces the generation of a specific storm in one modeled case that would not have formed in the absence of the urban area. This storm initiation over the city was done primarily by urban terrain’s disturbance of the near surface wind flow, leading to a surge of dynamically produced turbulent kinetic energy (TKE). The thermal production of TKE over the nighttime urban boundary layer, on the other hand, serves as a contributing factor to the storm formation.