Bhutan’s Himalayan river systems reflect a delicate balance between abundance and vulnerability, as monsoon‑driven flows and mountain hazards increasingly shape the country’s hydrological future.
Landlocked in the eastern Himalayas, Bhutan’s river basins are shaped by monsoon rains and snowmelt, giving the country one of the highest per capita water availabilities in the world. Its hydrology is structured around five main river basins: Amochhu, Wangchhu, Punatsangchhu, Mangdechhu and Drangmechhu. Smaller basins such as Jaldakha, Aiechhu, Jomori and Merak–Sakteng chhu complement this network. Monsoon rainfall and snowmelt feed these steep slopes, which release an estimated 70–71 billion m³ of water per year.
Bhutan’s very rugged topography sharpens spatial contrasts. The southern foothills, directly exposed to the monsoon, receive significantly more precipitation than the interior valleys and the northern high plateaus, which lie in more sheltered, leeward positions behind major mountain ranges.
Bhutan experiences a typical South Asian monsoon climate. The dry winter season extends from November to April and brings little precipitation. The wet season is concentrated between June and September, when the monsoon delivers about 72–80% of annual rainfall.
Winter is characterized by low river flows, as water is stored as snow at high elevations. In contrast, summer brings rising floods when intense rainfall combines with glacier and snowmelt. Peak discharges most often occur between July and August.
Climate analyses show increasing evapotranspiration, which intensifies water losses. MoreoProjections simultaneously indicate a rise in pre‑monsoon and monsoon rainfall in the south of the country.
Run‑of‑river hydropower plants dominate Bhutan’s energy mix. More than 60% of annual electricity generation occurs during the four monsoon months, forcing the country to import power from India in winter.
The country faces severe mountain hazards, amplified by extreme rainfall that triggers flash floods and landslides. In addition, its numerous glacial lakes have produced several glacial lake outburst floods (GLOFs). One such outburst devastated the Punakha valley in 1994, and, more recently, the Lemthang Tsho glacial lake outburst released an estimated 0.37 million m³ of water, and caused flooding that extended about 30 km downstream.
Only 63% of the population has continuous access to safe drinking water. The situation is particularly acute in rural areas, where drying springs leave communities facing water shortages during the dry season.
Recent policy responses now play a growing role in Bhutan’s water governance as the country faces intensifying climate stress. In October 2023, the government approved the National Hydromet Policy, which strengthens weather and climate services and supports earlier warnings for floods and glacial hazards.
Bhutan also launched ACREWAS, a five-year project that improves climate-resilient water supply, irrigation, catchment restoration, and climate-proof infrastructure in vulnerable districts. In 2024, the Ministry of Infrastructure and Transport also issued the Guideline for Inclusive and Climate-Resilient Rural Water Supply Services to improve potable water access under changing climate conditions.
As climate pressures intensify, these measures help Bhutan’s river basins adapt to droughts, floods, and glacial hazards.
