Read the full profile
Average annual precipitation is an estimated 1 500 mm (Table 2). Nepal has more than 6 000 rivers, which provide a dense network with steep topographic conditions. All rivers in Nepal drain into the Ganges river. The country is divided into five river basins, which are from west to east:
- Mahakali river basin, which is shared with India, with an average flow from the Indian tributaries into the border river, of arounds 15 km3/year and some 3.4 km3/year from the Nepalese tributaries.
- Karnali river basin, with an average outflow of about 43.9 km3/year.
- Gandaki river basin, with an average outflow of roughlys 50.7 km3/year;
- Kosi river basin, with an average outflow estimated as 47.2 km3/year, which receives a contribution of some 12 km3/year from the upper catchment area located in China; and the
- southern river basins, which produce some 65 km3/year of water flowing into India.
The seasonal distribution of flow is extremely variable. It might be as low as 1.5-2.4 percent of the total runoff in January, February and March, and as high as 20-27 percent in July and August for snowfed rivers, while the corresponding figures for purely rainfed rivers are 0.5-3 percent from March to May and 19-30 percent in July and August.
The surface water resources produced internally are estimated as 198.2 km3/year. The groundwater resources have not been fully assessed. Ongoing studies show that a good potential for groundwater extraction exists, especially in the southern terai lowland plains and inner valleys of the hilly and mountainous regions. Much of the terai physiographic region and some parts of siwalik valleys are underlain by deep or shallow aquifers, many of which are suitable for exploitation as sources of irrigation water. A rough estimate can be made by assuming a groundwater resource equivalent to 10 percent of surface water, i.e. approximately 20 km3/year, which corresponds to the base flow of the rivers. The total internal water resources would therefore amount to 198.2 km3/year. Chinese statistics mention an average outflow to Nepal of 12 km3/year, which brings the total renewable water resources of Nepal to 210.2 km3/year. It is assumed that all the renewable water resources of Nepal flow out of the country to India.
In 2009, the total dam capacity was 85 million m3, although the potential exists for at least 138 km3. Hydroelectricity accounted for more than 96 percent of total electricity generation. The two main diversion barrages are the Kosi and Gandaki reservoirs.