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The use of remotely sensed data particularly the NOAA AVHRR data was considered a major tool for such purpose. On a much wider scale, this kind of information could also be useful for global research and modeling, macro-economic studies, and assessment of the earth’s state of environment. The harmonization of land cover categories was adopted in the interpretation of satellite data for these countries towards a comprehensive regional resource assessment and information aggregation, an important decision input for the regional and national context.
Under this volume, the land cover of Nepal and its related information have been presented while the overall rational behind this activity and its associated methodology appeared in Volume 1-A. This Nepal’s Case Study made possible through the ICIMOD/MENRIS-Kathmandu contribution. It is envisioned that such results will serve as valuable information for a more direct and appropriate formulation of policies and sensible resource management strategies.
Location and Physical Characteristics
Nepal is divided into five major physiographic regions which run in more or less parallel bands from northwest to southeast. Each of these regions has a distinctive agricultural and forestry land utilization pattern. These regions are known as Terai, Siwaliks, Middle Mountains, High Mountains and High Himal from south to north direction. Nepal was once extensively covered by forests. Demand for fodder, overgrazing and uncontrolled cutting of timber and fuel wood, have significantly reduced the original forest cover. The composition of vegetation is closely related to the climate, which in turn is related to the physiographic region. There is not only a difference in vegetation from north to south, but also from east to west. The latter is caused by the decrease of monsoon rains in the western part and to some extent by the latitudinal differences between the eastern and western regions of Nepal.
The Terai – it forms a long strip of alluvial deposits along Nepal’s southern border with India. The strip is an extension of the broad Gangetic Plain, and includes the Bhabar regions, which consist of alluvial fans of the Siwaliks. Originally, the Terai was covered with dense jungle, mainly composed of sal (Shorea robusta) and mixed hardwoods. Following a steady migration of population, most of the forest have been cleared for cultivation, predominantly of rice. Large tracts of forest in the Terai can be found in the Bhabar areas, which are well drained and have a low water table. The soils of the Bhabar areas are generally coarse in texture, subject to erosion if mismanaged, and are not therefore as suitable for agricultural production as the other areas of the Terai. The Terai is not only important for its agricultural production, but also plays an important role in timber production and fuelwood supply. It also provides a rapid and economic east-west transportation corridor. Although the Terai represents only 14% of the total area of Nepal, it contains about 42% of the total cultivated land of the country. The forests consist mainly of high value sal and a mix of tropical and subtropical species.
The Siwaliks – its hillslopes have little potential for agricultural production. Soils are shallow and erodable.The majority of agricultural land is restricted to river terraces, alluvial valleys and, despite their limited areas to the Dun valleys. However, occasional hillslope cultivation may be found. The forests consist mainly of chir pine (Pinus roxburghii) and tropical mixed hardwoods of which sal is often a major component. The Siwaliks has very little agricultural land in the valley. The main crops are maize, millet, wheat and mustard. Rice is found where irrigation water is available.
Middle Mountains – this region has the highest population density in relation to cultivated land. The height of the Middle Mountains ranges from a few hundred meters to approximately 3,000 meters. The region is generally heavily dissected and has a great variety of soil types, geology and microclimates. Because of these, the area has many different agricultural landuse patterns. The farming systems incorporate a number of such land patterns as well as extensively used public forest and grazing areas. The land in the Middle Mountains is intensively cultivated. Existing pasture land is heavily overgrazed and forests are stripped for fodder and fuelwood. Most slopes are terraced and support maize, millet, rice, wheat or potatoes. It was found that 85% of the cultivated land of the Middle Mountains consists of some form of hillslope cultivation. The badly degraded forests of the Middle Mountains consist mostly of hardwoods with some conifers, mainly pine.
High Mountains – unlike the boundary between the Terai and Siwaliks, there is no clearly defined boundary between the High Mountains and the Middle Mountains. The steep slopes of the High Mountains often show intensive agricultural terracing. River terraces are less extensive than they are in the Middle Mountains since rivers tend to develop deep incisions which leave little room for valley cultivation. Upper limits of agricultural land are reached in this physiographic unit. On large, gently sloping fields, one crop of potato, buckwheat or barley may be grown once every year or every two years. Many of the snow fields serve as buffer reservoirs for irrigation water used in the lower regions. Extensive areas of grazing land are found in the form of alpine pastures. Migrating livestock from lower areas utilize the pastures of this area during the monsoon. The forests of this region include both coniferous and hardwoods. Some of the least disturbed forest, especially the conifer forests including fir (Abies spectabilis) and hemlock (Tsuga dumosa) are found in this region. In the High Mountains, upper limits of agriculture are found at about 4,200 meters. In the high regions, fields can support only one crop of buckwheat, barley or potato once a year or once every two years. The High Mountain forests contain a higher proportion of different conifers and in general, are in a better condition than forests elsewhere in the country.
High Himal – its climate is predominantly arctic, with permafrost, permanent snow fields and many glaciers. The little agricultural land available is found in the valleys and in some cases in sheltered pockets of the hillslopes. Pasture lands are used by migratory livestock in the High Mountain regions, and by yaks along the trade routes connecting Tibet.
The climate of Nepal varies from subtropical to arctic, all within a distance of approximately 180 kilometers. In addition to the broad differentiations in climate, there is a great variety of micro climatic conditions, resulting in a diversity of landuse and land practices within the country. In general, the climate of the Terai, Dun valleys, and part of the Siwaliks (up to 1000m) is subtropical. The climate of the Middle Mountains (1000-3000m ) ranges from warm temperate to cool temperate, and the high Mountains (2600-4000m) from cool temperate to sub-alpine.
The monsoon, which lasts from June to September, is the most outstanding feature of the climate in Nepal. The monsoon peaks in July and is accompanied by a northwesterly airflow from the Bay of Bengal. Hence, its onset is first experienced in the east of the country while the period from October to March is mainly dry. Occasional precipitation occurs in the form of winter rains, caused by an eastward airflow from the Mediterranean, with local surface heating and/or orographic effects. The influence of these winter rains tends to be stronger in the west than in the east. The rains are of great importance for winter crops such as wheat and barley. In the east of the country the pre-monsoon rains generally last longer, facilitating two monsoon crops in many areas.
The snowline lies around 2500 meters during the winter. Snow rarely falls below the 1500 meter level. On shaded north slopes, snow lingers on considerably longer than on south facing slopes. Farmers make use of this feature since irrigation water is released at a slow and steady pace. Many of the higher snow fields supply irrigation water to the lower agricultural land during most of the year.
Present State of Land cover
The total forest area is estimated to have declined from 6.4 million ha in 1964 to 5.5 million ha by 1985. About 0.2 million ha of the Terai and Siwaliks forests were cleared under planned settlement and because of illegal felling between the 1950s and 1985. (National Report on Nepal, UNCED-92). Further degradation of the forest lands has been observed in the years after 1985, and the reasons can easily be recognized by observing the population movements and the general physiography of the region. As reported by FAO (1991), the forest area is approximately 2,480,00 ha or 18% of the total land area. Further, arable land and permanent pasture accounted for 9% and 15%, respectively of the country.