There are over 600,000 hectares (ha) of irrigated farmland in Sri Lanka. Cultivation takes place during the two seasons with an average cropping intensity of 1.65.
The main irrigated crop in the country is paddy (94% of irrigated area), with an average yield of 4.3 tonnes (t)/ha, and a surplus is being produced at the moment. While the current productivity ranges between 0.2-0.5 kilograms (kg)/cubic meter (m3), the irrigation efficiency at systems level is about 35-45%. There is a growing need for substantial investment in the rehabilitation of existing irrigation facilities and overall improvements in productivity. Therefore, future investment in the irrigation sector needs to be more focused on increasing productivity of expensive irrigated water through increased yields and multiple use.
Managing groundwater use
As is happening elsewhere in Asia, farmers are increasingly turning to groundwater. Private investment in agro-wells and irrigation pumps is expanding rapidly because of the high rates of return on investment. Wells and pumps allow multiple-cropping of high-value upland crops, give farmers more discretion over water use, promote diversification of crops and livestock, and increase farmers’ incomes. Most of the new wells are running dry or producing low quality water due to site selection errors. However, indiscriminate withdrawal of groundwater from aquifers is a serious threat to the sustainable use of groundwater.
Moreover, nearly 30% of the population live in coastal areas and depend on the shallow lens of freshwater saddled on saline waters for livelihoods and for the tourism industry. These precious and limited water resources are threatened by over-extraction, pollution, saltwater intrusion and sea level rise due to climate change. No doubt, the sustainable utilization of this limited resource is important. A systematic research program is urgently needed to guide the policy, legislations and institutions that include adaptation to climate change.
Agriculture in the dry zone
The dry zone forms 70% of the land area of Sri Lanka. Most of the rain falls during the three months of the monsoon season in the form of heavy downpours. Therefore, the traditional practice was to capture and store this rainwater in small- and medium-size surface reservoirs. There are an estimated 18,0001 constructed ponds or tanks in the dry zone, but approximately half of them are classified as ‘abandoned’ or badly in need of repair. Some of these structures in this area can be traced back to the fifth century BC. Though these tanks served multiple purposes, irrigation has always played a major role in the economy. These small tanks are the ideal storage option for mitigating drought and floods, a function they have performed on a local scale for several centuries. These tanks are interlinked and interdependent through a cascade system. The rehabilitation of these tanks is of great interest to everybody. Past experiences show the failure of the single tank rehabilitation approach. Therefore, in rehabilitation efforts, one should look at the whole cascade system including the watershed area and not only on an individual tank. Large areas of land in the Dry Zone are under rainfed conditions. The productivity of rainfed areas could be increased by supplemental irrigation at crucial times for the crops using groundwater. This type of conjunctive use of water can help to improve the livelihoods of a vast amount of people, whose livelihoods are vulnerable to frequent droughts and floods.
Watershed degradation in the hill country and the impact on water resources and agriculture
Population pressure on lands in the hilly region is leading to the cultivation of marginal slopes. Forest cover is declining dramatically. This conversion of natural forest into agricultural and other land uses has decreased annual total water yield, increased storm runoff and reduced baseflows. About 31% of the electricity used in the country is generated from rivers flowing from the hills, and most irrigated lowlands depend on water from the hills. Poor land management practices and rapid runoff are responsible for high soil erosion, loss of land productivity, more frequent flash floods, and silting of canals and other water bodies. About 46% of the total land area in the hill country is estimated to be seriously affected by erosion.