The Ganges-Brahmaputra is one of the largest river basins in the world. This 1,634,900 square kilometres of basin spreads over Bangladesh, Bhutan, India, Nepal, and China (Tibet). The Ganges and Brahmaputra rivers both have their source in the Himalayas, where glacier melt water is an important source for the headwaters of the river. A number of studies have claimed in recent years that thanks to climate change, the Himalayan glaciers are melting more rapidly, and that can further bring major variation to the runoff of this river system (Yao et al. 2012). The Ganges River originates on the southern slope of the Himalayan range, and on its way seven major tributaries augment its fl ow. Three of them – the Gandak, Karnali (Ghagara), and Kosi – run through Nepal, and they supply approximately 60 per cent of the Ganges fl ow. After leaving Himalayas, the Ganges fl ows in the south-easterly direction through India, then forms the boundary between India and Bangladesh for about 112 kilometres before entering into Bangladesh. The Brahmaputra River originates from near Lake Mansarovar, and after fl owing in China (Tibet) in an easterly direction comes to the northeastern part of India, and then to Bangladesh to merge with the river Ganges in the middle of Bangladesh. The main tributary to the system, the Meghna River, originates in the northeastern region of India and then fl ows into Bangladesh to join the combined fl ow of the Ganges and Brahmaputra. Of the total basin area of this massive river system, 62.93 per cent is in India, 7.39 per cent in Bangladesh, 2.58 per cent in Bhutan, 8.02 per cent in Nepal, and 19.08 per cent in China (Tibet) (Verghese & Iyer 1993: 44).