Climate, Season and Environment of Nepal नेपालको हावापानी, ऋतु र वातावरण
Climate:
Altitudinal belts
Nepal's latitude is about the same as that of the United States state of Florida, however with elevations ranging from less than 100 meters (300 ft) to over 8,000 meters (26,000 ft) and precipitation from 160 millimeters (6 in) to over 5,000 millimeters (16 ft) the country has eight climate zones from tropical to perpetual snow.[5]
The tropical zone below 1,000 meters (3,300 ft) experiences frost less than once per decade. It can be subdivided into lower tropical (below 300 meters or 1,000 ft.) with 18% of the nation's land area) and upper (18% of land area) tropical zones. The best mangoes and well as papaya and banana are largely confined to the lower zone. Other fruit such as litchee, jackfruit, citrus and mangoes of lower quality grow in the upper tropical zone as well. Winter crops include grains and vegetables typically grown in temperate climates. The Outer Terai is virtually all in the lower tropical zone. Inner Terai valleys span both tropical zones. The Sivalik Hills are mostly upper tropical. Tropical climate zones extend far upriver valleys across the Middle Hills and even into the Mountain regions.
The subtropical climate zone from 1,000 to 2,000 meters (3,300 to 6,600 ft) occupies 22% of Nepal's land area and is the most prevalent climate of the Middle Hills above river valleys. It experiences frost up to 53 days per year, however, this varies greatly with elevation, proximity to high mountains and terrain either draining or ponding cold air drainage. Crops include rice, maize, millet, wheat, potato, stone fruits and citrus.
The great majority of Nepal's population occupies the tropical and subtropical climate zones. In the Middle Hills, "upper-caste" Hindus are concentrated in tropical valleys which are well suited for rice cultivation while Janajati ethnic groups mostly live above in the subtropical zone and grow other grains more than rice.
The Temperate climate zone from 2,000 to 3,000 meters (6,600 to 9,800 ft) occupies 12% of Nepal's land area and has up to 153 annual days of frost. It is encountered in higher parts of the Middle Hills and throughout much of the Mountain region. Crops include cold-tolerant rice, maize, wheat, barley, potato, apple, walnut, peach, various cole, amaranthus and buckwheat.
The Subalpine zone from 3,000 to 4,000 meters (9,800 to 13,100 ft) occupies 9% of Nepal's land area, mainly in the Mountain and Himalayan regions. It has permanent settlements in the Himalaya, but further south it is only seasonally occupied as pasture for sheep, goats, yak and hybrids in warmer months. There are up to 229 annual days of frost here. Crops include barley, potato, cabbage, cauliflower, amaranthus, buckwheat and apple. Medicinal plants are also gathered.
The Alpine zone from 4,000 to 5,000 meters (13,100 to 16,400 ft) occupies 8% of the country's land area. There are a few permanent settlements above 4,000 meters. There is virtually no plant cultivation although medicinal herbs are gathered. Sheep, goats, yaks and hybrids are pastured in warmer months.
Above 5,000 meters the climate becomes Nival and there is no human habitation or even seasonal use.
Arid and semi-arid land in the rainshadow of high ranges have a Transhimalayan climate. Population density is very low. Cultivation and husbandry conform to subalpine and alpine patterns but depend on snowmelt and streams for irrigation.
Precipitation generally decreases from east to west with increasing distance from the Bay of Bengal, source of the summer monsoon. Eastern Nepal gets about 2,500 mm (100 in) annually; the Kathmandu area about 1,400 mm (55 in) and western Nepal about 1,000 mm (40 in). This pattern is modified by adiabatic effects as rising air masses cool and drop their moisture content on windward slopes, then warm up as they descend so relative humidity drops. Annual precipitation reaches 5,500 mm (18 ft) on windward slopes in the Annapurna Himalaya beyond a relatively low stretch of the Lower Himalayan Range. In rainshadows beyond the high mountains, annual precipitation drops as low as 160 mm (6 in).
Seasons:
The year is divided into a wet season from June to September—as summer warmth over Inner Asia creates a low-pressure zone that draws in moist air from the Indian Ocean—and a dry season from October to June as cold temperatures in the vast interior create a high-pressure zone causing dry air to flow outward. April and May are months of intense water stress when cumulative effects of the long dry season are exacerbated by temperatures rising over 40 °C (104 °F) in the tropical climate belt. Seasonal drought further intensifies in the Siwaliks hills consisting of poorly consolidated, coarse, permeable sediments that do not retain water, so hillsides are often covered with drought-tolerant scrub forest. In fact, much of Nepal's native vegetation adapted to withstand drought, but less so at higher elevations where cooler temperatures mean less water stress.
The summer monsoon may be preceded by a buildup of thunderstorm activity that provides water for rice seedbeds. Sustained rain on average arrives in mid-June as rising temperatures over Inner Asia creates a low-pressure zone that draws in moist air from the Indian Ocean, but this can vary up to a month. Significant failure of monsoon rains historically meant drought and famine while above-normal rains still cause flooding and landslides with losses in human lives, farmland and buildings.
The monsoon also complicates transportation with roads and trails washing out while unpaved roads and airstrips may become unusable and cloud cover reduces safety margins for aviation. Rains diminish in September and generally end by mid-October, ushering in generally cool, clear, and dry weather, as well as the most relaxed and jovial period in Nepal. By this time, the harvest is completed and people are in a festive mood. The two largest and most important Hindu festivals—Dashain and Tihar (Dipawali)—arrive during this period, about one month apart. The post-monsoon season lasts until about December.
After the post-monsoon comes the winter monsoon, a strong northeasterly flow marked by occasional, short rainfalls in the lowlands and plains and snowfalls in the high-altitude areas. In this season the Himalayas function as a barrier to cold air masses from Inner Asia, so southern Nepal and northern India have warmer winters than would otherwise be the case. April and May are dry and hot, especially below 1,200 meters (4,000 ft) where afternoon temperatures may exceed 40 °C (104 °F).
Environment
The dramatic changes in elevation along this transect result in a variety of biomes, from tropical savannas along the Indian border, to subtropical broadleaf and coniferous forests in the hills, to temperate broadleaf and coniferous forests on the slopes of the Himalaya, to montane grasslands and shrublands, and finally rock and ice at the highest elevations.
This corresponds to the Terai-Duar savanna and grasslands ecoregion.
Subtropical forests dominate the lower elevations of the Hill region. They form a mosaic running east–west across Nepal, with Himalayan subtropical broadleaf forests between 500 and 1,000 meters (1,600 and 3,300 ft) and Himalayan subtropical pine forests between 1,000 and 2,000 meters (3,300 and 6,600 ft). At higher elevations, to 3,000 meters (10,000 ft), are found temperate broadleaf forests: eastern Himalayan broadleaf forests to the east of the Gandaki River and western Himalayan broadleaf forests to the west.
The native forests of the Mountain region change from east to west as precipitation decreases. They can be broadly classified by their relation to the Gandaki River. From 3,000 to 4,000 meters (10,000 to 13,000 ft) are the eastern and western Himalayan subalpine conifer forests. To 5,500 meters (18,000 ft) are the eastern and western Himalayan alpine shrub and meadows.
Environmental issues
- Natural hazards
- Earthquakes, severe thunderstorms (tornadoes are rare[6]), flooding and flash flooding, landslides, drought, and famine depending on the timing, intensity, and duration of the summer monsoons
- Environment - current issues
- Deforestation (overuse of wood for fuel and lack of alternatives); contaminated water (with human and animal wastes, agricultural runoff, and industrial effluents); wildlife conservation; vehicular emissions
- Environment - international agreements
- Party to: Biodiversity, Climate Change, Climate Change-Kyoto Protocol, Desertification, Endangered Species, Hazardous Wastes, Law of the Sea, Ozone Layer Protection, Tropical Timber 83, Tropical Timber 94, Wetlands
- Signed, but not ratified: Marine Life Conservation
- Existing and proposed dams, barrages and canals for flood control, irrigation and hydroelectric generation
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