기후변화에 맞서 스리랑카의 농민들이 고대의 관개 체계를 활용하자고 요구

Ancient irrigation reservoirs have played an important role in Sri Lanka’s agriculture and could be even more vital now due to changing weather patterns, new research has found. Thomson Reuters Foundation/Amantha Perera

This time last year, most of Sri Lanka was baking amid a drought that lasted 10 months. Reservoirs had run dry in the main food-growing regions in the north and east, where farmers had seen no rain since the end of 2011.

This year could not be more different. The monsoon season has been in full force since the last week of May, after five months of intermittent but heavy rainfall. Sri Lanka’s main reservoirs - vital for the island’s power production and agriculture - are full to the brim.

The Ceylon Electricity Board said in mid-June that the nine reservoirs driving hydro-power generation are able to meet 92 percent of current electricity supply needs. A year back, their capacity was only around 20 percent.

But government officials are not taking any chances. “You would be surprised to know that not only do we track oil prices (and) projections at the Monetary Board meetings, we also keep track of how much water there is in the reservoirs,” Ajith Nivard Cabraal, governor of Sri Lanka’s Central Bank, recently told journalists.

Cabraal said the bank’s concern was motivated by the significant impact of rainfall on both power generation and agricultural production.

But while the problem of erratic rains may seem relatively new, research by Sri Lankan water experts shows that a workable solution to the vagaries of shifting rain patterns has been around for centuries in the form of ancient irrigation reservoirs, or “tanks” as they are known locally.

Experts at the Colombo-based International Water Management Institute (IWMI) say these tanks – mainly located in the north and east – can be used to store excess water from floods, which is then released during dry spells.

Nishadi Eriyagama, a water resources engineer at the IWMI, said farming regions in the dry zone have traditionally relied on reservoirs and irrigation for crop cultivation.

“It has been the custom from ancient times to store excess rainfall in large and small irrigation ‘tanks’ to be used during the dry season,” she told Thomson Reuters Foundation.

‘CRITICAL TO SURVIVAL’

One example is the Parakarama Samudraya tank in north-central Polonnaruwa District. Spanning an expanse of 20 sq km, it was dug out in the 12th century BC and has an 18 km-long outer wall.

It provides water for most of the district’s crops, according to R. M. Karunaratane, the officer in charge of irrigation.

“When the tank is full, like now, there are few problems in the district. But when it runs dry, we have farmers protesting on the streets, burning tyres,” the official said. Last July, farmers surrounded his office, blaming engineers for their water woes.

As rainfall patterns change, it will be vital to have some way of at least partially controlling the water in the reservoir, he added.

“People don’t understand clearly that we can only release water if we have it in the reservoir. When there is no water, my office is the main target of their anger,” he explained.

There are thousands of such tanks in Sri Lanka, concentrated in the drier north and east. Most are relatively small, serving one or two villages.

K.B. Gunapala, a farmer in north-central Anuradhapura District, said the three tanks that provide water to his village of Tambalagollawe determine the annual harvest.

The tanks fill up during the rainy season, after which the water is used for cultivation. “They are critical to the village’s survival,” Gunapala said. 

RESTORATION NEEDED

When the tanks were constructed, their main purpose was to store water for the dry season. But they can also help control floods and protect crops from flood damage, IWMI’s Eriyagama said.

Nonetheless, only sporadic efforts have been made to restore individual tanks and their irrigation networks, and there has yet to been a major, island-wide rehabilitation effort, Eriyagama added.

The IWMI research, which was carried under the CGIAR Research Programme on Climate Change, Agriculture and Food Security (CCAFS), also found that other methods have also been effective in dealing with shifting rainfall patterns in Sri Lanka, including rain water harvesting.

Sonja Vermeulen, head of research for the CCAFS programme, told Thomson Reuters Foundation the new research highlights the importance of supporting farmers’ efforts to manage climate stresses, despite inconclusive evidence on the impact of more extreme weather trends.

“It is imperative that countries take decisive action on adaptation to climate change, rather than wait for a global movement take place,” she said.

Vermeulen said the Sri Lankan example shows that local, indigenous knowledge and practices can sometimes be put to good use quickly, rather than waiting for newer technologies that could take years and millions of dollars to develop.