Distinct urban land cover response to meteorology in WRF simulated pre-monsoon thunderstorms over the tropical city of Kolkata

The Kolkata metropolitan region, located in eastern India, is one of the most densely urbanized areas, with significant thunderstorms reported during the pre-monsoon season. The Weather Research and Forecasting (WRF) model is used to investigate the influence of urban-induced land use and land cover (LULC) change over Kolkata during the pre-monsoon thunderstorms. Multiple thunderstorm events reported during 2014-2017 are simulated using a high (H-urb) and low (L-urb) urban LULC scenario. The presence of higher urban pixels in H-urb case favors the enhancement in precipitation mainly over central and northern parts of the city in the downwind direction. Urban Heat Island (UHI) effect is more evident during the nighttime, with a temperature difference of up to 0.5 degrees C. However, the UHI impacts the vertical structure of the boundary layer (BL) more during the daytime due to prevailing higher temperatures and dominant surface heating. The analysis reveals positive contributions of the ground and sensible heat fluxes to the near-surface UHI intensity. The surfaces over the urban patch and surrounding areas experience a relatively drier atmosphere than their rural counterparts. Over the identified urban patches, a significant impact on meteorological variables is seen near the surface and within the BL in the case of H-urb compared to L-urb LULC scenario. The urbanization over Kolkata stimulates the BL and the local meteorology encouraging nighttime UHI, afternoon or evening moist convection, and consequent occurrence of thunderstorms to result in enhanced and distinctly distributed rainfall over the city and its neighborhood during pre-monsoon months.

Automated summary

This study investigates the impact of urbanization and land use change on rainfall during pre-monsoon thunderstorms in Kolkata using a weather model. The results show that higher levels of urbanization are associated with increased precipitation, particularly in central and northern parts of the city. The urban heat island effect is more pronounced at night, with a temperature difference of up to 0.5 degrees Celsius. Urbanization also affects the vertical structure of the boundary layer, with a greater impact during the daytime. The study also finds that urban areas experience a drier atmosphere compared to rural areas.