Thursday, October 25, 2007

Bangladesh rainfall variability: Impact of climate change?

Daily Star (Bangladesh), by Dr. Rashed Chowdhury: The Ganges-Brahmaputra-Meghna (henceforth, GBM) river system is the third largest freshwater outfall to the world's oceans. The Ganges and the Brahmaputra fall in a number of countries in the South Asian region, including China, India, Nepal, and Bangladesh. Of these China contributes solely to the flow of the Brahmaputra, and Nepal to the flow of the Ganges. These two rivers often overflow during the monsoon months, and the flow reduces dramatically in the dry season. The region therefore faces two major hazards: floods during the monsoon and scarcity of water during the dry season. These hazards become more pronounced in the downstream regions particularly in Bangladesh.

Increasing population and accelerating economic development activities in the basin of the Ganges and the Brahmaputra river system have now made the sustainable water management of the region even more critical than in the past. The sharing of water resources has long been a matter of dispute among the four co-basin countries. …The situation is particularly critical for Bangladesh as about 80 percent of its annual fresh water supply comes as transboundary inflows through 54 common rivers with India.

The effects of climate on hydrology in Tropical Asia would have many facets. In the Himalayas, the storage of precipitation in the form of snow and ice (in glaciers) over a long period provides a large water reservoir that regulates annual water distribution. The majority of rivers originating in the Himalayas have their upper catchments in snow-covered areas and flow through steep mountains. If there is any climatic variability in the Himalayas the impacts could be felt in the downstream countries -- that is, India and Bangladesh. By and large, dry-season flow in the major Himalayan rivers in a given year results from the monsoon rainfall of the previous year. If there is any climatic change in the mountain hydrological regimes, it is likely to alter these resources, and severely affect Bangladesh that depends on this water resource….

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