The kingdom of Nepal is a landlocked country which lies along the southern slopes of the Himalaya Mountains, with India on its southern, eastern, and western borders, and the Tibetan Autonomous Region of the Peoples' Republic of China to the north. The country has a land area of 147, 180km2, being 800km from east to west, and varying from 144km to 240km north to south, between longitudes 80°–88°E and latitudes 26°–31°N. Within Nepal's borders lie some of the most deeply incised and geologically active regions in the world, and over 70% of the country is covered by mountains of varying altitude.
Three main physical regions can be defined based broadly upon altitude. To the south of the country is the Terai which is low, 50–100masl, and is a northern extension of the Gangetic Plains of India. The topography of the area is flat, and the soils are generally very fertile, consisting of alluvial deposits carried down in the rivers from the hills and mountains to the north. This zone ranges from 25–32km in width.
Rising from the Terai plains and following an east/west alignment, are two ranges of hills generally referred to as the “Mid-hills” which range in altitude from 1300–2500masl and which are known as the Siwalik (or Churia) Hills at lower altitudes and the Mahabharat Lekh range at higher elevations. Between the Mahabharat Lekh and the high Himalayas are another series of mountains commonly referred to as the “High-hills” which cover the elevations from 2500–5000masl, these being a transitional zone and aligned generally north/south as a result of the rivers draining through them from the high Himalayas. To the north of these High-hills are the Himalayas proper, again aligned east/west, which include the highest mountains in the world and range from 5000–8800masl. These last two zones are either only sparsely inhabited, or are totally uninhabited, with most land above 5500m being permanently snowbound.
It follows, that the climate and therefore the natural environment of the country are influenced by two factors. First, Nepal is situated in sub-tropical latitudes so that temperatures at low altitudes are inherently warm to hot. Superimposed upon, and modifying this potentially subtropical climate are both the effects of altitude and aspect, which result in great diversity of microclimatic conditions with respect to temperature and rainfall, so that the natural environment can show great variation within a particular location.
The climate of the Terai is subtropical, with the natural seasons being determined by the monsoon rains which affect the entire Indian subcontinent. As the low to mid-hills (1300–2500masl) are encountered, the climate is classified as warm temperate, and above this, between 2500 and 4500masl cool-temperate. The high hills (2500 to 5500m), comprise an alpine zone, while above 5500m, the temperature is almost always below freezing point.
Rainfall varies from as little as 500mm per annum in the rainshadow areas to the north of the high Himalayas to over 5000mm in areas to the south of some of the major Himalayan massifs. For most of the country average rainfall lies between 900mm and 1900mm per annum, becoming progressively drier from the east to the west. The greater part of this rain falls during the monsoon between the middle of June and the end of September.
Under such conditions of climatic variability there is a wide diversity of climax vegetation. Where the climate is subtropical on the Terai and in the lower hills, then tropical forest trees such as khair (Acacia catechu), sissoo (Dalbergia sissoo), and sal (Shorea robusta) are the dominant species. In the mid-hills, deciduous trees such as poplars (Populus spp.), oaks (Quercus spp.), walnut (Juglans regia) and larch (Larix spp.) in association with evergreens such as pines (Pinus spp.) and rhododendrons (Rhododendron spp.) predominate. Between 3000–4000m asl, rhododendron, mixed with birch (Betula spp.) and fir trees occur, while the zone below the timber line of the high mountains contains spruce, fir, cypress, juniper and birch. Alpine pasture occurs at high altitude below the permanent snowline (4500–5000m asl) and has traditionally afforded valuable grazing land during the summer monsoon months.
At present, about one third of the country is still covered by natural forest, but most of this is confined to the less accessible slopes of hills and mountains. On the Terai, there has been severe overexploitation of natural sal woodland leading to its degradation and consequent loss of land use potential, through physical erosion of the soil, and a decline in its fertility.
In geological terms, Nepal is still a young country, and the theory of plate tectonics asserts that the Indian subcontinent is still moving northwards with the result that the Himalaya Mountains are still rising. The hills and mountains abutting the Himalayan Massif are still geologically active, and regular earthquakes of considerable magnitude are a feature of the country. The mountain and hill slopes are therefore steep and inherently unstable. Even without human intervention, landslides and other mass movements of soil are frequent, particularly during the monsoon season, when rainwater water percolates down to the bedrock, and acts as an effective lubricant.
No comments:
Post a Comment