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Bhutan: An Introduction

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Bhutan is a mountainous country, where mountains and hills occupy most of the land. Out of the 2,400 km long Himalayan range, the Bhutan Himalayas extend up to 340 km. The country is vulnerable to various hazards due to fragile geological conditions, great elevation differences, and steep sloping terrain. Apart from landslides and river erosion, the mountainous region is also quite susceptible to disastrous hazards due to glacial lake outburst floods (GLOFs).

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Bhutan is situated in the eastern Himalayas between the latitudes 26 45 N to 28 10 N and longitudes 8845 E to 9210 E. It is 340 km in length with an approximate area of 40,077 sq. km. It is bordered by the Tibetan plateau of China in the north and the Indian States of Sikkim in the west, West Bengal, and Assam in the south, and Arunachal Pradesh in the east. The terrain is mostly rugged and mountainous with elevations ranging from 200 metres above sea level to above 7,000 metres above sea level within a distance of less than 175 km. The area above 4,200 metres above sea level covers 20.5% of the total land and is covered by the perpetual snow and ice forming the glaciers and glacial lakes. The variation of the climate is extremely dependent on the altitude.

Bhutan has three regions that are open to visitors. These three regions are distinctly different due to the prominent north, south mountain ranges that separate each area resulting in different topographical features. (source: http://www.kingdomofbhutan.com)

Western Bhutan

Western Bhutan is comprised of the Haa Valley at 8860ft. (recently opened to limited travel), Paro Valley at 7200ft., Thimphu at 7500ft. the Punakha Valley and Wangdue Phodrang at 4200ft., separated by high passes or "La's": Cheli La (3988m, 13,084ft.), Dochu La (3050m, 10,007ft.), Pele La (3300m, 10,825ft., separates Western from Central). Western Bhutan is known for its stunning scenery with rice paddies and orchards cascading down magnificent mountains, the pristine rivers that flow through the main towns of Paro, Thimphu and Punakha, and unique two-story houses with brightly painted window designs.

Central Bhutan

The Black Mountains separate Western Bhutan from Central Bhutan. This region includes Trongsa and the rich broad valleys of Bumthang including Chumey, Choekhor, Tang and Ura valleys. The passes crossed are Yotang La (3400m, 11,155ft.) Shertang La (3573m, 11,723ft) and Thrumshing La (3800m, 12,465ft.). Central Bhutan is known for its buckwheat and apple production, its sturdy stone houses, and its plethora of monasteries. Its the ideal place for walking due to its broad valleys and sloping mountains. The beauty of the Bumthang valley is legendary.

Eastern Bhutan

This region comprises Mongar, Lhuentse, Trashigang and Trashi Yangste. Sengor Valley separates Central from Eastern Bhutan. After Thrumshing La, passes crossed are Kori La (2400m), Yongphu La (2190m) and Narphung La (1698) at much lower altitudes than Western and Central. The forests dissipate and the altitude is lower. The warmer climate is suitable for growing corn, rice, wheat, potatoes and surprisingly lemon grass. Eastern Bhutan is known for its stunning hand-loomed textiles and the weavers are all masters of the supplementary weft-weave technique. Eastern Bhutan is the least traveled area of the country.

Climate

Bhutans climate is influenced mainly by the monsoon wind, which blows in from the Bay of Bengal, local topography and the variations in elevation as one move from south to the north. In general, the climate is characterized by dry winter and wet summer monsoon, and the temporal variations in climate are correspondingly extreme.

Although it is a relatively small country with maximum north-south distance of 170 km and maximum east-west distance of 300 km, the regional variations in climatic conditions within Bhutan are rather extreme, mainly due to the difference in altitude, which vary from approximately 100 metres above sea. in the Southern Foothills to 7,500 metres above sea. at the border to China in the Northern High Himalayas. Thus, while the southern Bhutan is generally hot and humid, the high Himalayan Mountains in the northern borders of the country experiences severe alpine climate and are under perpetual snow. However, the climate can vary considerably between the valleys and within the valleys depending on levels of altitude, and aspects. Rainfall, in particular, can differ considerably within relatively short distances due to rain shadow effects.

From past records the mean annual rainfall varies approximately from 2,500 to 5,500 mm in the southern foothills, from 1,000 to 2,500 mm in the inner valleys, and from 500 to 1,000 mm in the northern part of the country.

River System

Being a landlocked country, Bhutans water resources are mainly in the form of rivers. There are quite a few lakes, but they are mostly small and are mainly located in the remote high altitude alpine areas and are not much of economic utility. Some of these lakes are glacial lakes, and outburst of these lakes from time to time has resulted in enormous flash floods and damage to lives and property.

Due to the topographic nature of the country, the major rivers flow north to south, with their sources in the perpetual snow cover and flowing right down to the tropical zone on the border with India. While most of them originate in Bhutan itself, a few of them have their origin in China. These rivers have steep longitudinal gradients and narrow steep gorge, which occasionally open up and provide broader valleys with small areas of flat land for cultivation. Some of the main rivers have cut 1,000 metres deep valleys through the mountains. The majority of the valleys are narrow V-shaped valleys indicating that water erosion has been the main cause of forming them. Due to the steep longitudinal gradients and the high annual runoff, these rivers provide significant hydropower potential, with an estimated theoretical potential of 30,000 MW.

Due to the existence of distinct rainy and dry seasons, there are large seasonal variations in the river flows. They carry large volumes of flow and often also sediment during the monsoon season, whereas the flow is relative low during the dry season due to the limited rainfall and the limited existence of major groundwater reservoirs. Snowmelt from the high altitude alpine areas in the north contributes to the flow at the end of the dry season. Apart from the major north-south flowing rivers, Bhutan consist of a dense network of small perennial and rain-fed - tributaries that flow down the steep slopes and side valleys, often as waterfalls, to join the major rivers.

Bhutans water resources are confined in four major river basins: Amochhu, Wangchhu, Puna-Tsangchhu and Manas River. They all originate from the high altitude alpine area and from the perpetual snow cover in the north and flows into the Brahmaputra River in the Indian plains.

The Amochhu has its origin in China and flows through the western districts of Ha and Samtse before it finally drains into the plains of India.

The Wangchhu consists of three major tributaries from the three valleys of Thimphu, Paro and Ha. They originate within Bhutan from the glaciers and snow-capped mountains in the north. It flows south to the Indian plains through Chhukha district.

Another major river system is the Puna-Tsangchhu (or Sankosh Chhu), which consists of the two major tributaries Pho and MoChhu that originates from Gasa district. The two rivers join at Punakha Dzong to become Punatshangchu (Sankosh) that flows through Wangdue Phodrang, Tsirang and Sarpang districts before reaching the Indian Plains.

The biggest river basin is the Manas River, which drain almost all of the catchments of the Central and Eastern Bhutan. It consists of four major sub-basins: Mangde Chhu and Chamkhar Chhu, (which both originate close to Gankhar Punsum), Kuri Chhu, (which originate from China) and Dangme Chhu, which originates from the northern- eastern part of TrashiYangtse, Aurunacha Pradesh in India and from China. Three minor rivers drain the south-eastern corner of the country: Nyera Ama Chhu, Nonori Chhu and Jomo Chhu.

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