Influence of the monsoonal activity and hydrological conditions on big floods over Bengal delta
Abstract
Bangladesh is a delta of the mighty rivers Ganges and Brahmaputra, originate in the glaciers of Himalayan Mountains. A number of streams originate in the Himalayan foothills and enter into Bangladesh to form the river Meghna. All these rivers pass through Bangladesh before falling to the Bay of Bengal. Being situated in the heart of the South Asian monsoon region, Bangladesh is highly prone to devastating floods. More than normal monsoon rainfall in the catchments of these rivers in the upstream and over Bangladesh produces devastating floods over the country. The study investigates the hydrological and meteorological conditions favourable for the formation of the big floods of 1988, 1998, 2004, 2007 and 2020. The study uses satellite images (INSAT 3D and METEOSAT satellites) to identify the monsoonal activities related to floods. The rainfall data from TRMM and GPM satellites are used to investigate the spatial and temporal pattern of rainfall over Bangladesh and its adjacent areas. The river discharge data are obtained from the Bangladesh water Development Board (BWDB) (from 1980 to 2016) and satellite measurements (from 1998 to 2020) at 3 stations on the Brahmaputra (lat: 25.514, lon: 89.775), Ganges (lat: 24.974, lon: 87.975) and Meghna (lat: 24.70, lon: 92.93) are analyzed. The pressure/geopotential and wind fields are analyzed over the surface level: 500 mb and 200 mb over a relatively large domain covering Indian and Pacific Oceans. The following finding seems to be of interest.
The floods aggravate when the peaks of the river-discharge coincide in the major rivers. The rainfall over Bangladesh and in the upper catchments is high when the monsoon trough moves towards extreme north and its axis passes over Bangladesh. The trough activates the monsoon rainfall over Bangladesh and adjacent areas to its north, east and west. At this time land depressions form and provide heavy rainfall for about 4-5 days or more over these areas. Sometimes the monsoon depressions move to Bangladesh and remain more than 3 days producing devastating floods. The spatial analysis of the surface pressure field and its anomaly shows that the anticyclone over the north Pacific intensifies and extends high-pressure towards the North Bay, when the monsoon trough shifts to north, at the same time a weak trough/secondary ITCZ is formed over the South Bay.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMH197.0010Q
- Keywords:
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- 1821 Floods;
- HYDROLOGY;
- 1847 Modeling;
- HYDROLOGY;
- 1855 Remote sensing;
- HYDROLOGY;
- 4333 Disaster risk analysis and assessment;
- NATURAL HAZARDS