Geography of Bhutan

Landlocked, Bhutan is situated in the eastern Himalayas and is mostly mountainous and heavily forested. It is bordered for 470 kilometers by Tibet (China's Xizang Autonomous Region) to the north and northwest and for 605 kilometers by India's states of Sikkim to the west, West Bengal to the southwest, Assam to the south and southeast, and Arunachal Pradesh  to the east. Sikkim, an eighty-eight-kilometer-wide territory, while West Bengal separates Bhutan from Bangladesh by only sixty kilometers. At its longest east-west dimension, Bhutan stretches around 300 kilometers; it measures 170 kilometers at its maximum north-south dimension, forming a total of 46,500 square kilometers. 

Bhutan is covered 70 percent with forests; 10 percent is covered with year-round snow and glaciers; nearly 6 percent is permanently cultivated or used for human habitation; another 3 percent is used for shifting cultivation (tsheri), a practice banned by the government; and 5 percent is used as meadows and pastures. The rest of the land is barren rocky areas or scrubland.

In the north, the snowcapped Great Himalayan Range reaches heights of over 7,500 meters above sea level and extends along the Bhutan-China border. The northern region consists of an arc of glaciated mountain peaks with an arctic climate at the highest elevations. Watered by snow-fed rivers, alpine valleys in this region provide pasturage for livestock tended by a sparse population of migratory shepherds. Early Visitors to Bhutan reported "dark and steep glens, and the high tops of mountains lost in the clouds, constituted altogether a scene of extraordinary magnificence and sublimity." One of the most rugged mountain terrains in the world, it has elevations ranging from 160 meters to more than 7,000 meters above sea level, in some cases within distances of less than 100 kilometers of each other. Bhutan's highest peak, at 7,554 meters above sea level, is north-central Kulha Gangri, close to the border with China; the second highest peak, Chomo-Lhari, overlooking the Chumbi Valley in the west, is 7,314 meters above sea level; nineteen other peaks exceed 7,000 meters.  

The Inner Himalayas are southward spurs of the Great Himalayan Range. The Black Mountains, in central Bhutan, form a watershed between two major river systems, the Mo-Chhu and the Drangme Chhu (chhu means river). Peaks in the Black Mountains range between 1,500 meters and 2,700 meters above sea level, and the fast-flowing rivers have carved out spectacular gorges in the lower mountain areas. The woodlands of the central region provide most of Bhutan's valuable forest production. Eastern Bhutan is divided by another southward spur, the Donga Range. Western Bhutan has fertile, cultivated valleys and terraced river basins.

In the south, the Southern Hills, or Siwalik Hills, the foothills of the Himalayas, are covered with dense deciduous forest, alluvial lowland river valleys, and mountains that reach to around 1,500 meters above sea level. The foothills descend into the subtropical Duars Plain. Most of the Duars Plain proper is located in India; and ten to fifteen kilometers penetrate inside Bhutan. The Bhutan Duars has two parts. The northern Duars, which abuts the Himalayan foothills, has rugged, slopping terrain and dry porous soil with dense vegetation and abundant wildlife. The southern Duars has moderately fertile soil, heavy savanna grass, dense mixed jungle, and freshwater springs. Taken as a whole, the Duars provides the greatest amount of fertile flatlands in Bhutan. Rice and other crops are grown on the plains and mountainsides up to 1,200 meters. Bhutan's most important commercial centers—Samchi, Phuntsholing, Geylegphug, and Samdrup Jongkhar-are located in the Duars, reflecting the meaning of the name, which is derived from the Hindi language "dwar" means gateway. Rhinoceros, tigers, leopards, elephants, Beers and other wildlife inhabit the region.

Climate

Bhutan's climate is as varied as its altitudes and, like most of Asia, is affected by monsoons. North-Western Bhutan is particularly affected by monsoons that bring between 60 and 90 percent of the region's rainfall. The climate is humid and subtropical in the southern plains and foothills, temperate in the inner Himalayan valleys of the southern and central regions, and cold in the north, with year-round snow on the main Himalayan summits.

Temperatures vary according to elevation. Temperatures in Thimphu, located at 2,200 meters above sea level in west-central Bhutan, range from approximately 15° C to 26° C during the monsoon season of June through September but drop to between about -4° C and 16° C in January. Most of the central portion of the country experiences a cool, temperate climate year round. In the south, a hot, humid climate helps maintain a fairly even temperature range of between 15° C and 30° C year-round, although temperatures sometimes reach 40° C in the valleys during the summer.

Annual precipitation ranges widely in various parts of the country. In the severe climate of the north, there is only about forty millimeters of annual precipitation--primarily snow. In the temperate central regions, a yearly average of around 1,000 millimeters is more common, and 7,800 millimeters per year has been registered at some locations in the humid, subtropical south, ensuring the thick tropical forest, or savanna. Thimphu experiences dry winter months (December through February) and almost no precipitation until March, when rainfall averages 20 millimeters a month and increases steadily thereafter to a high of 220 millimeters in August for a total annual rainfall of nearly 650 millimeters.

Bhutan's generally dry spring starts in early March and lasts until mid-April. Summer weather commences in mid-April with occasional showers and continues through the pre-monsoon rains of late June. The summer monsoon lasts from late June through late September with heavy rains from the southwest. The monsoon weather, blocked from its northward progress by the Himalayas, brings heavy rains, high humidity, flash floods and landslides, and numerous misty, overcast days. Autumn, from late September or early October to late November, follows the rainy season. It is characterized by bright, sunny days and some early snowfalls at higher elevations. From late November until March, winter sets in, with frost throughout much of the country and snowfall common above elevations of 3,000 meters. The winter northeast monsoon brings gale-force winds down through high mountain passes.

River Systems

Bhutan has four major Chhu (river) systems: the Drangme Chhu; the Puna Tsang Chhu (also called the Sankosh in the south); the Wang Chhu; and the Amo Chhu. Each flows swiftly out of the Himalayas, southerly through the Duars to join the Brahmaputra River in India, and thence through Bangladesh where the Brahmaputra (or Jamuna in Bangladesh) joins the mighty Ganges (or Padma in Bangladesh) to flow into the Bay of Bengal. The largest river system, the Drangme Chhu, flows southwesterly from India's state of Arunachal Pradesh and has three major branches: the Drangme Chhu, Mangde Chhu, and Bumthang Chhu. These branches form the Drangme Chhu basin, which spreads over most of eastern Bhutan and drains the Tongsa and Bumthang valleys. In the Duars, where eight tributaries join it, the Drangme Chhu is called the Manas river. The 320-kilometer-long Puna Tsang Chhu rises in northwestern Bhutan as the Mo Chhu and Pho Chhu, which are fed by the snows from the Great Himalayan Range. They flow southerly to Punakha, where they join to form the Puna Tsang Chhu, which flows southerly into India's state of West Bengal. The tributaries of the 370-kilometer-long Wang Chhu rise in Tibet. The Wang Chhu itself flows southeasterly through west-central Bhutan, drains the Ha, Paro, and Thimphu valleys, and continues into the Duars, where it enters West Bengal as the Raigye Chhu. The smallest river system, the Tursa Chhu, known as the Amo Chhu in its northern reaches, also flows out of Tibet into the Chumbi Valley and swiftly through western Bhutan before broadening near Phuntsholing and then flowing into India.  Glaciers in northern Bhutan, which cover about 10 percent of the total surface area, are an important renewable source of water for Bhutan's rivers. Fed by fresh snow each winter and slow melting in the summer, the glaciers bring millions of liters of fresh water to Bhutan and downriver areas each year. Glacial melt added to monsoon-swollen rivers, however, also contributes to flooding and potential disaster.