tailieunhanh - Climate Change and Water Resources in South Asia - Chapter 5

Bangladesh nằm trong đồng bằng của ba con sông lớn - sông Hằng, Brahmaputra và Meghna (GBM), thường được gọi là một Với một mạng lưới phức tạp của 230 con sông, bao gồm 57 con sông ranh giới chéo, khoảng 92,5 "đất của các con sông và nước." % của 175 triệu ha (MHA) của diện tích lưu vực kết hợp của các sông GBM (Hình ) là vượt ra ngoài ranh giới của Bangladesh và được đặt tại Trung Quốc, Nepal, Ấn Độ và Bhutan. Vì vậy, Bangladesh hoạt động như một ổ cắm hệ thống thoát nước. | 5 The Implications of Climate Change on River Discharge in Bangladesh M. MONIRUL QADER MIRZA INTRODUCTION WATER RESOURCES PROBLEM OF BANGLADESH Bangladesh lies in the delta of three large rivers - the Ganges Brahmaputra and Meghna GBM which is often termed as a land of rivers and water. With a complex network of 230 rivers including 57 cross boundary rivers about of the 175 million hectares mha of combined basin area of the GBM Rivers Fig. is beyond the boundary of Bangladesh and is located in China Nepal India and Bhutan. Therefore Bangladesh acts as a drainage outlet for the cross-border runoff. More than 90 of the annual runoff is generated outside of Bangladesh. However there is a high seasonal difference in the availability of water. For example for the Ganges River the ratio of dry and monsoon runoff is 1 6 Fig. . This illustrates that Bangladesh has an abundance of water in the monsoon while the country still faces surface water scarcity in the dry season. Irrigated agriculture is highly dependent on dry season surface water availability. On average annually floods engulf roughly of the area of the country or about mha Mirza 2003 . In extreme cases floods may inundate about 70 of Bangladesh as it occurred during the floods of 1988 and 1998 Ahmed and Mirza 2000 . Hydrological droughts are very common in the rivers of Bangladesh. The magnitude of precipitation over the GBM basins is very high and more than three-quarters occurs during the summer monsoon June-September Table . The resulting huge volume of cross-border monsoon runoff together with the locally generated runoff and some physical factors either singly or in combination causes floods in Bangladesh. The physical factors either singly or in combination include snow and glacier melt El Nino Southern Oscillation ENSO induced conditions loss of drainage capacity due to the siltation of principal distributaries backwater effect unplanned infrastructure development .