First results from the Doppler Weather Radar observations over Mumbai urban region during the inter-seasonal phases of 2018 monsoon

Globally many urban areas, including the coastal megacity of Mumbai, have witnessed the increasing threat of heavy rainfall and flooding in recent decades. This paper provides the first results of a radar campaign that has been set up to study the precipitation systems over Mumbai in 2018. Results indicate that the coastal city experiences heavy rainfall spells during both the pre-monsoon and monsoon periods and the convective systems originate from the eastern and western parts of the region, respectively. The collocated observations of clouds and precipitation fields identify a distinct diurnal variation in rainfall occurrences with three peaks for the pre-monsoon period. No such features were evident during the monsoon months. The rainfall peaks correspond to an intense meso-convective environment as observed from the S-band doppler radar. The feedback of the urban convective environment during the pre-monsoon period and the offshore moisture supply to the city during the monsoon months are the likely contributing factors for these contrasting diurnal behaviour. The microphysical characteristics of rainfall show that the raindrops of diameter greater than 1.5 mm dominate the pre-monsoon months compared to the monsoon period. The convective urban environment characterized by higher localized CAPE aids strong thermals leading to smaller drops shifting aloft and allowing bigger drops to precipitate locally during the pre-monsoon season.