Growth in mid-monsoon dry phases over Indian region:Prevailing influence of anthropogenic aerosols

Abstract. A detailed investigation on the potentially drought prone regions over India has been presented in this study based on the balance between precipitation and potential evapotranspiration (PET) during the South West Asian mid-monsoon season. We methodically introduce a parameter named dry day frequency (DDF) which is found suitable to present the drought index (DI) in mid-monsoon season hence strongly associated with the possibility of drought occurrences. The present study investigates the probable aspects which influence the DDF over these regions revealing that the abundance of anthropogenic aerosols especially over urbanized location have prevailing role on the growth of DDF during last few decades. The prominent increasing trend in DDF over Lucknow (26.84° N, 80.94° E), a densely populated urban location situated in the Indo-Gangetic plain, strongly reflects the dominant association of man-made aerosols with the increasing dry phase occurrences. Increase in DDF (~ 90 %) during the last 60 years is observed over this urban area compared to a broader region in its surroundings. In addition, periodic impacts of synoptic scale phenomena like ENSO (El Nino–Southern Oscillation) or SSN (Sun spot number) become weaker when the study location is downscaled towards an urbanized region. However, there still remains some unclear role of air-mass transport on DDF over the potential drought prone region of north-west India. Finally, when long term projections of DDF are drawn using the high urbanization scenario of RCP 8.5 a huge rise in dry days are seen during mid-July to mid-September (reaching up to 50 dry days by the year 2100 over Lucknow) which will be a very crucial concern for policy makers in future.