Sri Lanka lies on the Indian Plate, a major tectonic plate that was formerly part of the Indo-Australian Plate. It is in the Indian Ocean southwest of the Bay of Bengal, between latitudes 5° and 10°N, and longitudes 79° and 82°E. Sri Lanka is separated from the Indian subcontinent by the Gulf of Mannar and Palk Strait. According to Hindu mythology, a land bridge existed between the Indian mainland and Sri Lanka. It now amounts to only a chain of limestone shoals remaining above sea level. Legends claim that it was passable on foot up to 1480 AD, until cyclones deepened the channel. Portions are still as shallow as 1 metre (3 ft), hindering navigation.
The island consists mostly of flat to rolling coastal plains, with mountains rising only in the south-central part. The highest point is Pidurutalagala, reaching 2,524 metres (8,281 ft) above sea level. The climate is tropical and warm, due to the moderating effects of ocean winds. Mean temperatures range from 17 °C (62.6 °F) in the central highlands, where frost may occur for several days in the winter, to a maximum of 33 °C (91.4 °F) in other low-altitude areas. Average yearly temperatures range from 28 °C (82.4 °F) to nearly 31 °C (87.8 °F). Day and night temperatures may vary by 14 °C (25.2 °F) to 18 °C (32.4 °F).
Rainfall pattern is influenced by monsoon winds from the Indian Ocean and Bay of Bengal. The "wet zone" and some of the windward slopes of the central highlands receive up to 2,500 millimetres (98.4 in) of rain each year, but the leeward slopes in the east and northeast receive little rain. Most of the east, southeast, and northern parts of Sri Lanka comprise the "dry zone", which receives between 1,200 and 1,900 mm (47 and 75 in) of rain annually.
The arid northwest and southeast coasts receive the least amount of rain at 800 to 1,200 mm (31 to 47 in) per year. Periodic squalls occur and sometimes tropical cyclones bring overcast skies and rains to the southwest, northeast, and eastern parts of the island. Humidity is typically higher in the southwest and mountainous areas and depends on the seasonal patterns of rainfall.
An increase in average rainfall coupled with heavier rainfall events has resulted in recurrent flooding and related damages to infrastructure, utility supply and the urban economy.
Sri Lanka has 103 rivers. The longest of these is the Mahaweli River, extending 335 kilometres (208 mi). These waterways give rise to 51 natural waterfalls of 10 meters or more. The highest is Bambarakanda Falls, with a height of 263 metres (863 ft). Sri Lanka's coastline is 1,585 km long. Sri Lanka claims an Exclusive Economic Zone (EEZ) extending 200 nautical miles, which is approximately 6.7 times Sri Lanka's land area. The coastline and adjacent waters support highly productive marine ecosystems such as fringing coral reefs and shallow beds of coastal and estuarine seagrasses.
Sri Lanka has 45 estuaries and 40 lagoons. Sri Lanka's mangrove ecosystem spans over 7,000 hectares and played a vital role in buffering the force of the waves in the 2004 Indian Ocean tsunami. The island is rich in minerals such as ilmenite, feldspar, graphite, silica, kaolin, mica and thorium. Existence of petroleum and gas in the Gulf of Mannar has also been confirmed and the extraction of recoverable quantities is underway.
Flora and fauna
Lying within the Indomalaya ecozone, Sri Lanka is one of 25 biodiversity hotspots in the world. Although the country is relatively small in size, it has the highest biodiversity density in Asia. A remarkably high proportion of the species among its flora and fauna, 27% of the 3,210 flowering plants and 22% of the mammals, are endemic. Sri Lanka has declared 24 wildlife reserves, which are home to a wide range of native species such as Asian elephants, leopards, sloth bears, the unique small loris, a variety of deer, the purple-faced langur, the endangered wild boar, porcupines and Indian pangolins.
Flowering acacias flourish on the arid Jaffna Peninsula. Among the trees of the dry-land forests are valuable species such as satinwood, ebony, ironwood, mahogany and teak. The wet zone is a tropical evergreen forest with tall trees, broad foliage, and a dense undergrowth of vines and creepers. Subtropical evergreen forests resembling those of temperate climates flourish in the higher altitudes.
Yala National Park in the southeast protects herds of elephant, deer, and peacocks. The Wilpattu National Park in the northwest, the largest national park, preserves the habitats of many water birds such as storks, pelicans, ibis, and spoonbills. The island has four biosphere reserves: Bundala, Hurulu Forest Reserve, the Kanneliya-Dediyagala-Nakiyadeniya, and Sinharaja.Of these, Sinharaja forest reserve is home to 26 endemic birds and 20 rainforest species, including the elusive red-faced malkoha, the green-billed coucal and the Sri Lanka blue magpie.
The untapped genetic potential of Sinharaja flora is enormous. Of the 211 woody trees and lianas within the reserve, 139 (66%) are endemic. The total vegetation density, including trees, shrubs, herbs and seedlings, has been estimated at 240,000 individuals per hectare. The Minneriya National Park borders the Minneriya tank, which is an important source of water for numerous elephants (Elephus maximus) inhabiting the surrounding forests. Dubbed "The Gathering", the congregation of elephants can be seen on the tank-bed in the late dry season (August to October) as the surrounding water sources steadily disappear. The park also encompasses a range of micro-habitats which include classic dry zone tropical monsoonal evergreen forest, thick stands of giant bamboo, hilly pastures (patanas). and grasslands (talawas).
Sri Lanka is home to over 250 types of resident birds. It has declared several bird sanctuaries including Kumana. During the Mahaweli Program of the 1970s and 1980s in northern Sri Lanka, the government set aside four areas of land totalling 1,900 km2 (730 sq mi) as national parks. Sri Lanka's forest cover, which was around 49% in 1920, had fallen to approximately 24% by 2009.