Why the Drought?


by Dr.C.S. Weeraratna

In Sri Lanka, rain is the primary source of water. The annual rainfall is around 1,800 mm with areas such as Hambanthota and Mannar receiving only about 900 mm and some areas in the hill country receiving about 5,000 mm. The total amount of water received in the form of rain is around 100 billion cubic meters per year. In spite of the country receiving so much rain, water reservoirs, wells and other water sources etc in many districts of the country, mainly in the dry zone, are dry/drying affecting cultivation of paddy and upland crops . A few millions of inhabitants in these areas are facing immense difficulties due to non availability of water for drinking and other domestic purposes. Shortage of water has also affected hydro power generation reservoirs such as Victoria, Randenigala etc. and the animals in these areas.

Water Use

The National Water Supply & Drainage Board supplies treated pipe-borne water to about 44% of the population. Around 3,500 Community Based Organizations supply water to nearly four million people in rural areas. These water supply schemes use reservoirs, village tanks, protected /unprotected shallow wells, deep wells with hand pumps or motorized pumps as water sources.

Water stored in reservoirs is taken to paddy lands located in the low-lands by an intricate system of channels. Around 500,000 hectares of paddy lands are cultivated using water from such reservoirs numbering about 12,000 which store the run off water. These tanks constructed to collect rainwater for crop and animal production and various domestic uses are an integral part of the eco-system, and play a dominant role in the socio-economic and cultural aspects of villages. Most of the 12,000 tanks are not distributed randomly, but in the form of distinct cascades each made up of 4-10 small tanks situated within a single small catchment of 100-1000 hectares.

Rainwater that falls on to the ground infiltrates and the balance runs-off. Infiltration is promoted by organic matter levels in the soil. But, most of the soils, especially those in the high rainfall areas are eroded and cannot retain much water thus favouring run-off. Out of the 100 billion cubic meters of water received annually it is estimated that around 60 billion cubic meters of water escape to the sea, although we often speak of the famous dictum of King Parakramabahu I, according to which "let not even one drop of water that falls on the earth in the form of rain be allowed to reach the sea without been used"

Thus, the main reason for water shortage in many parts of the country is high surface run-off.. central highlands of Sri Lanka which is the watershed feeding major rivers in Sri Lanka that immensely contribute to agriculture, power generation and water for human consumption receives an annual rainfall of 2500 – 5000 mm. The top soil in the central highlands has got eroded to a considerable extent resulting a drop in its capacity to retain the rain water. . According to a number of studies, the loss of top soil due to water erosion in the tea lands in the central highlands could be around 40 t/ha/yr causing the soil depth to decrease by 30-50 c.m annually. Felling of trees also promote run-off. It is reported that the catchment areas of many reservoirs/tanks are cultivated. Buildings have come up in some of the catchments. All these activities promote run-off. Run-off water carries a heavy load of silt and clay which gets deposited in reservoirs reducing its capacity to store water. It is because of this that most tanks spill after a few days of rain, and dry up after a few weeks of dry weather.

Rainwater Harvesting

Rainwater collection has been practiced since time immemorial. Rainwater is the most pure form of water. The rainwater that falls on the roofs of extensive buildings such as hospitals, schools, housing complexes etc. in urban areas can be collected in tanks in the premises itself. Water thus collected could be used for numerous domestic purposes. This will reduce water bill, save purified water and prevent flooding in some areas. Rainwater that falls over a period of one year on a roof of 1000 sq meter in Anuradhapura District , where drought affects to a great extent is around 1000 cubic meters ( 1 million liters) .

It is because of the importance of rainwater harvesting, Dinesh Gunawardena, the Minister of Water Supply and Drainage has taken action to promote rainwater harvesting in Sri Lanka. In June 2005, he initiated the formulation of a National Policy and strategy for rsain water harvesting which was approved by the government of Sri Lanka. The policy objective is aimed at encouraging communities to control water near its source by harvesting rain water. This would minimize the use of treated water for secondary purposes, reduce flooding, promote soil conservation and groundwater recharge, provide water for domestic use and crop production and reduce energy consumption. However, rainwater harvesting is not widely practiced and as a result a substantial amount of rainwater is not used.

Thus, drought is mainly because of our inability to use effectively 100 billion cubic meters of rain we get every year.

International Conference

The Ministry of Water Supply and Drainage of Sri Lanka together with National Water Supply & Drainage Board ( NWS&DB), National Community Water Trust (NCWT) and Lanka Rain Water Harvesting Forum ( LRWHF) is organizing a two day International conference under the theme " Water for Community Development and Prosperity" At this conference around 35 papers related to water supply issues will be presented and discussed. Based on the deliberations of this conference, appropriate actions will be taken to solve the issues/problems related to water supply.


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