Geography of Sri Lanka-

Climate, Relief and Distribution of Population

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In respect of relief the Island may be divided into five major regions:-
(1)The central Highlands, including the Knuckles and the Rakwana massif.
(2)The well-watered southwest country, having a characteristic topography of scarp lands, cuestas, hogs backs, strike ridges, with
gentle dip slopes and steeper scarp edges, alternating with longitudinal valleys and showing a well developed trellis drainage
(3)The drier, east and south-east country of residual hills, monadnocks, buttes, and monolithic outcrop domes, with a morphology of the inselberg type.
(4)The northern lowland and slope with residual ridges and hills, diminishing gradually in height and width with distance from the central highlands, eventually to be buried under the mantle of recent alluvium and gravels.
(5)The coastal belt of lowland, including the fringe of lagoons, spits, and dunes.

The central highlands are situated in the south central region of Sri Lanka. These highlands have a highly dissected terrain consisting of plateaus, ridges, escarpments, and inter-montane basins and valleys. The highest mountains of Sri Lanka, Pidurutalagala(8281 ft.or 2524 metres),Kirigalpotta(7858 ft or 2395 metres), and Adam's Peak (7,559 ft.or 2303 metres) are all situated in this area. The highlands are defined by a series of escarpments, the most spectacular being the so-called World's End, a near vertical precipice of about 4,000 ft.
Another important feature in the central highlands is the existence of a series of flats or plains at varying

1).Horton Plains -mean altitude 7,000 ft.
2).Moon plains,Elk plains,kandapola,Ambewala -6,200 ft.
3).The Ragala ledge- 4,900 ft.
4).The Hatton and Madulsima platform- 4,500 ft-4,200 ft.
5).The Welimada basin-4,200 ft.
6).the Southern platform, Kandy plateau, and the Badulla basin-2,000-1,600ft.
7).The Mahavalatanna-Tanjantanna step-1,500-1,200 ft.

The presence of these plains had a bearing on siting of settlements and agricultural land use.

The south-central highlands is an extensive and lofty mountain zone, commonly known as the upcountry. It is a cool, healthy and invigorating region, well watered by perennial streams and rivers which frequently descend in picturesque waterfalls and rapids. It is endowed with a luxuriant natural vegetation and posses great scenic attractions. The panoramas presented from it's passes and commanding heights being exceptionally expansive and beautiful.



Sri Lanka being a tropical country situated closer to the equator, has mainly a tropical climate. The temperatures are perennially high, but there are variations in temperature between the lowlands and the central highlands, determined more by the elevation rather than the season. Higher the elevation cooler is the temperature .In the lowlands the average monthly temperature varies from 26 deg. celsius to about 31 deg. celsius around thr year. However in the central highlands the monthly average varies between 7 deg. celsius and 22 deg. celsius. In Nuwara Eliya situated at an elevation of 1,525 metres the monthly average vary from about 13 deg, celsius in December to 20 deg.celsius in May.


The predominant factor that influences the climate of the country is the occurrence of two regional wind systems known as the Monsoon winds that blow in opposite directions across the Island at different times of the year.

During the first Monsoon period that occurs between May to October, the winds blow in a south-westerly direction, and bring rain-laden clouds from the Indian Ocean. There is heavy rainfall during this period affecting mainly the southern and western parts of the country and the central highlands.

In the second monsoon period that takes place between December and March, the winds reverse direction and blow from the north-east, bringing moisture-laden clouds from the Bay of Bengal. The north-east Monsoon brings rain to the north-east as well as the central highlands, and the southern and western parts of the country. In between the two Monsoon periods there are short inter-Monsoon periods which bring normal convectional rains,

Thus based on the precipitation received the Country can be divided into two main climatic zones:-
(1)The wet zone
(2)The dry zone


The wet zone receives rain from both the south-west and north-east Monsoons, as well as the inter-Monsoon period. The annual precipitation in this region varies from 80 ins.(2,032 mm) to 200 ins.(5,080 mm) and is evenly distributed throughout the year. The wet zone can be divided into the low-country wet zone and the montane or up-country wet zone.


The low-country wet zone extends over three provinces-the Western Province, the Southern Province' and the Sabaragamuwa Province-consisting of the following districts:-Gampaha, Colombo, Kalutara, Galle, Matara, Ratnapura and Kegalle. The average annual rainfall varies between 80ins. to 125 ins.(2,032mm-3,175mm),and rises to 130 200 ins(3302 mm to 5080 mm) in the Ratnapura and Kalutara districts, parts of Kegalle and Galle districts and the lower valley of the Kelani Ganga. In this region floods are a recurrent problem. The vegetation is luxuriant and dense, and farmers in this area have to struggle
continuously to control the growth of weeds that can invade cleared and cultivated land. The rivers are perennial, broad and deep. the need to store water for irrigation does not arise, as there is no lack of water at any time. Sometimes droughts do occur but they are not prolonged and do not cause any serious problems. The land is flat only near the Sea coast, but rises gradually inwards, often interrupted by high outcrops, to the foothills of the central mountains.

In modern Sri lanka the main population centres are all situated in the low-country wet zone,but in ancient times before 10th century A.D., there is no evidence of any settled population in the south-western region from Kalu Ganga in Kalutara to Nilwala Ganga in Matara, and in the Ratnapura district, which lies immediately inland of it. The earliest inscriptions from this region belongs to the 10th century A.D. It is recorded that in the 12th century A.D.Parakramabahu I drained the swamps and marshes of Pasdun Korale in Kalutara district,into the rivers and made the land habitable. However inscriptions recovered from Colombo, Gampaha, and Kegalle districts and Chilaw, show that these areas were populated in pre-Christian times.


The up-country wet zone extends over the entire south-central highlands, that include the Central and Uva Provinces, consisting of the following districts:-Kandy district, Matale district, Nuwara-Eliya district and Badulla district. The average rainfall is 80 125 ins (2,032 mm -3,175 mm), rising to 140 ins. to 200ins.(3,556 mm-5080 mm) in the upper valley of the Mahaweli Ganga around Ramboda and the Knuckles, and falling away to 65 100 ins (1,651 mm to 2,540 mm) in the mountains of Uva and the easterly hills, which form a drier sub-zone. The wettest town in Sri Lanka, Watawala, having the highest annual rainfall of over 200 ins.(5080 mm) is situated in this region.

The Montane zone above 2,500 ft.(762 metres) was largely unpopulated till the 10th century, but large scale movement of people into the hills did not take place untill the fall of the Polonnaru kingdom and the virtual abandonment of the northern plains in the 13th Century. However by the end of the Ist Century B.C.the lower montane zone between 1,000 ft to 2,000 ft.(305 metres to 610 metres) in elevation, was populated as indicated by rock inscriptions left in the Buddhist monasteries, mainly in the regions such as the Mahaweli Ganga valley, around Teldeniya, Kandy, and Gampola, and the lesser hills to the north-west of Badulla and the northern and western slopes of the Matale hills. The Kandyan Kingdom, the last stronghold of the Sinhalese Monarchy, was essentially a mountain kingdom, a refuge of independence from the European enemies below.


The low-country dry zone is historically the most important region in Sri Lanka, because it was the cradle of the Sinhalese Civilization. The main population centers in ancient times were situated in this region, including the kingdoms of the Sinhalese Monarchies from the 6th century B.C. up to the 13th Century A.D. The highly sophisticated irrigation systems consisting of vast irrigation tanks and an intricate system of irrigation channels, that has marveled and earned the respect and admiration of modern day Scientists and Engineers, was developed in this region, and was responsible for converting the dry zone into the main food producing area of the country.

The dry zone embraces the north-western, northern, north-eastern, north-central, eastern, and south-eastern parts of Sri Lanka, which constitutes about 70% Of the total land area. The provinces that fall under this area are the North-Western, North-Central, Eastern, Northern and parts of Uva and Southern Provinces. The districts that come under this area are Puttalam, Anuradhapura, Polonnaruwa, Batticaloa, Trincomalee, Digamadulla, Jaffna,Vanni, Moneragala and Hambantota.

The dry zone receives rain only during the north-east Monsoon between the months of December and March, while during the south-west Monsoon it undergoes a period of drought. The average annual rainfall is between 50 ins. to 75 ins.(1,270 mm to 1,905 mm) and decreases to 30ins. to 45ins. (762 mm to 1,143 mm) in the two arid sub-zones, Hambantota in the south-east and Mannnar-Puttlam in the north-west.

During the annual drought the temperature rises and a strong dry south-west wind blows throughout the day .The grass dries up and turns to stubble and can be easily set on fire. The vegetation droops and the under-growth dies out. The smaller irrigation tanks dry up or shrink to muddy pools. The streams and water courses run dry. The larger rivers except the Mahaweli Ganga and Walawe Ganga, are reduced to mere trickle of flowing water or break up into disconnected pools. Thus the main problem in the dry zone is the lack of an adequate supply of water during the annual drought, for agricultural and domestic purposes.

The ancient Sinhalese fully realizing this drawback in the dry zone areas, built a sophisticated irrigation system, consisting of large and small reservoirs, some rain fed and others receiving water along artificial canals from rivers that were dammed at higher levels. The creation of this vast irrigation network was a great boon to the population of the dry zone, in overcoming water shortages during he annual drought period, as well as at times when the north-east Monsoon rains failed.

After the fall of the Polonnaru Kingdom early in the 13th Century,the North-Central Province was abandoned ,and the vast irrigation systems were neglected and fell into total ruin. Malaria became a serious scourge and large scale population movements took place from the dry zone, towards the low-country and up-country wet zone regions, which subsequently became the main population centers of country. The re-occupation and re-development of the dry zone was possible only in the recent past after the second world war, following the extensive use of the insectide DDT to eradicate the Malarial vector, the Anopheles mosquito.

After the eradication of Malaria in the early 1940s,the Government embarked upon a massive re-construction and re-habilitation project, the primary aim of which was to reconstruct and restore the major ancient irrigation tanks and channels in the dry zone, and encourage farmers in re-occupying the land which they abandoned during the Malarial scourge. Independent Sri Lanka's first Prime Minister Honorable Don Stephen Senanayake was deeply involved in these projects, and was also instrumental in the construction of a massive irrigation project in the Eastern Province, under the Gal oya development scheme ,which resulted in the creation of a vast irrigation tank, known as the Senanayake Samudra, that supplied much needed water to thousands of acres of old and new paddy lands, and led to the establishment of new settlements and townships

However, the perennial problem of water shortages in other parts of the dry zone persisted until the Government of Sri Lanka in the decade 1980 to 1990 embarked upon the most ambitious development project ever undertaken in post-independent Sri Lanka
known as the Mahaweli Ganga diversion project,in which the longest, perennial river in Sri Lanka was dammed at several places,creating artificial lakes,the waters of which were subsequently channeled through underground and overland irrigation channels,to join the existing ancient network of irrigation channels and vast irrigation tanks situated in the North-Central and Eastern Provinces, thus providing adequate water supplies to these tanks ,for irrigated agriculture during the annual drought period. Hydro-Electric power was also generated at several points, under this massive irrigation cum hydropower project, thus giving a major boost to hydro-electric power generation in the country. The project has now been successfully completed and thousands of acres of new land have been brought under cultivation of rice and other food and cash crops. Simultaneously new farmer settlements have sprung up all over the North-central and Eastern Provinces .This has helped to reduce the rural-urban drift of the population. Thus Sri Lanka is one of the few developing countries, where the majority of the population still live in rural areas. The country has also achieved self-sufficiency in rice, the staple diet of the majority of Sri Lankans. Before the implementation of the Mahaweli Ganga diversion project,a failure in the north-east Monsoon, would have meant disaster for the farmers living in the area. But now, such occurences have become a thing of the past.

Much of the credit for the successful implementation of the Mahaweli Ganga diversion Project should go to the first executive President of Sri Lanka, who is also the father of the free market economy in the country, Honourable Junius Richard Jayewardene,who entrusted the vital development project, to his able and efficient Minister of Lands, Power and Irrigation, Honourable Gamini Dissanayake, setting an ambitious time frame of six years for the completion of the project. The project was re-named as the Accelerated Mahaweli Development Project and was completed with assistance from the World Bank and other friendly countries such as the U.S.A., the U.K., Canada, Germany, Sweden, etc.

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