Semi-quantitative precipitation forecasts for Kosi/Mahananda catchment by synoptic analogue method

Abstract

An attempt has been made to issue semi-quantitative precipitation forecasts for Kosi/Mahananda catchment by synoptic analogue method. Based upon 22 years of data (1982 - 2003) the study reveals that it is possible to issue semi-quantitative forecasts with confidence. Local topography of the catchments and its steep gradient from Bhimnagar to hatra/Brahkshetra in Kosi and hills in Darjeeling are favourable regions where moist air masses of the Bay of Bengal and the Arabian Sea during South West Monsoon in lower troposphere converge and trough at 500 hPa especially diffluent in rear creates divergence and moist air mass is pulled up resulting in heavy/very heavy rainfall in sub montane districts of Bihar and Nepal Himalaya in addition to orographic effects. This gives birth to severe floods and makes the life of densely populated districts of Pumea/Katihar/Saharsa/Kisanganj/Madhepura miserable and badly affects the economy of the region.