Snow and glacier cover in the western Himalaya region are very important because four major rivers—the Indus, Ganga, Brahmaputra, and Yamuna—originate there. Changes in snow and glacier cover influence the discharge and flow of these perennial rivers, which together constitute one of the world's largest alluvial river basins, the Indo-Gangetic (IG) basin. This basin is agriculturally fertile and densely populated with 700 million people. In the past, the basin has experienced numerous floods due to snow melting and also due to excessive monsoon rainfall. However, in recent years the areal extent of snow has been declining, especially in the western Himalayan region that has a direct influence over the hydrological regime of the basin and that also plays an important role in the changing climatic conditions of the Indian subcontinent.