dimanche 4 mai 2014

Geography of Sri Lanka (Draft)

From http://ramsar.wetlands.org/Portals/15/SriLanka.pdf

Area: 65,610 sq.km.
Population: 14,850,000 (1981).

Sri Lanka is a pear-shaped island in the Indian Ocean, situated between latitudes 5°54'N and 9°52'N, and longitudes 79°39'E and 81°53'E, and separated from India by a channel only 35 km wide at its narrowest. The island measures 435 km from north to south, and 225 km from east to west at its widest. 

Sri Lanka became an island probably in the late Miocene times (from 23 to 5 million years ago), the southwestern sector having been the first to separate from India, with alternate shallow floodings and elevations at various  times thereafter. There are also indications that parts of the island have, through subsidence, elevation, erosion and even faulting, produced three peneplains or erosions levels, at sea level to 120m, 300m to 700m, and 910m to 2,438m, respectively. Two-thirds of the island is lowland, with the highlands, at a general elevation of l, 400-l,800m, covering some 10,400 sq.km in the south-central part of the country. That the island is a detached part of the continental Deccan plateau is evident from its continental shelf and rock formations. Nine-tenths of the island is composed of crystalline rocks of pre-Cambrian age (Cooray, 1967). The greater part of the lowland is composed of very strongly metamorphic Palaeozoic rocks of the Vijayan series. There are areas of Miocene limestone in the northwest and southeast, and very small patches of fossiliferous Jurassic formations in the northwest (Puttalam) and Sabaragamuwa Province (Ratnapura). Plio-Pleistocene gravels occur as isolated patches in the northwest and southeast, and there are quaternary deposits in river valleys and along much of the east and west coasts.

Climatically, three major areas can be recognized. The overall climate is monsoonal with a southwest monsoon in May to August, and a northeast monsoon in October or November to January. The largest climatic area is the low country dry zone; this includes almost the entire northern half of the island, together with much of its eastern side, as far as the southeast coast. Although heavy rains occur during the northeast monsoon, the region is otherwise hot and dry, and is mostly covered with secondary forest and scrub. The annual rainfall ranges from 600 to 1,900 mm. The climate in the southwestern lowlands is very different, and is generally hot and humid, the annual rainfall on occasions exceeding 5,000 mm. The rainfall is concentrated into the period of the southwest monsoon, but also occurs during the northeast monsoon. The highlands also lie within this wet zone, but have a subtropical to temperate climate, depending on altitude.

In the lowlands, temperatures are typically tropical, varying from about 24°C to 32°C. However, at higher elevations much lower temperatures are recorded (10-20°C), and the temperature occasionally approaches zero at localities such as Nuwara Eliya, Horton Plains and Mount Pidurutalagala. In the lowlands, the mean average temperature is about 27°C, in the mid-country about 24°C, and in the highlands about 15°C. There are only slight seasonal variations in temperature, the fluctuations being 1.8°C at the coast, 2.7°C in the uplands and 2.4°C in the highlands.

Although large areas of the island are under cultivation, especially for tea and rubber, there arestill some significant areas of dense jungle remaining. The natural forest cover is presently estimated at approximately 23% of the total land area. Most of this (20%) is in the dry zone low country, while only 3% is in the wet zone, including the hill country. Since the control of malaria in the 1950s, most land development has taken place in the dry zone, especially in the basins of the Mahaweli Ganga and the southeastern rivers (MacKinon & MacKinnon, 1986).