Countering climate change with the cascade effect
A small-reservoir revival in Sri Lanka’s Dry Zone
By Samurdhi Ranasinghe, Communications Officer, IWMI
In 2017, Sri Lanka experienced one of its worst droughts in over four decades. This was the culmination of five consecutive years of dry weather during the country’s main crop production season. Drought hit the northern Dry Zone especially hard, causing significant reductions in the production of rice, a central pillar of national food security.
In support of the government’s response to this disaster, researchers with the International Water Management Institute (IWMI) have joined a major effort to rehabilitate “tank” (or small reservoir) cascade systems in the Dry Zone. Involving extensive fieldwork, IWMI’s research forms part of a large-scale project aimed at strengthening the resilience of smallholder farming in the face of extreme weather events, which are expected to occur more frequently as a result of climate change.
Sri Lanka’s tank cascade systems are the product of an ancient hydraulic civilization dating back some 2,500 years. Successive kings built extensive networks of tanks and reservoirs connected by canals, through which runoff from the upper tanks flows into the lower ones. Though often not well maintained, these systems continue to play a vital role in the everyday lives of rural people across the Dry Zone. Apart from being the main water source for irrigation, they supply water for fishing, washing, bathing and replenishing as well as the surrounding flora and fauna. Proper functioning of the tank cascade systems is vital to offset increasingly frequent dry spells in the region. Rehabilitation of the tanks requires meticulous planning, based on an integrated approach.
“Village irrigation systems, consisting of small tanks, are not only for production but rather have wider social, cultural and economic significance,” said Herath Manthrithilake, who heads IWMI’s Sri Lanka Development Initiative. “Any intervention aimed at improving the cascade systems must be implemented in ways that are environmentally sound and economically viable.”
To this end, the Ministry of Mahaweli Development and Environment, with assistance from the United Nations Development Programme (UNDP), has secured financing from the Green Climate Fund (GCF) to rehabilitate selected tanks through the Climate Resilient Integrated Water Management Project, taking place from 2017 to 2024. The project is focusing on three river basins in the northern part of the Dry Zone – Malwathu Oya, Mi Oya and Yan Oya – selected on the basis of two main factors. First, all three of these basins encompass cascade and village irrigation systems, on which smallholder farmers depend for their livelihoods. And second, compared with other basins, these are considered to be among the most vulnerable to extreme weather and climate change.
IWMI researchers have embarked on a pilot study of the hydrological, socio-economic and environmental conditions as well as the institutional setting in the Malwathu Oya River Basin. During the project’s first 2 years, they have collected primary and secondary data, and carried out field studies to help determine priorities and define criteria for rehabilitating tank cascade systems.
“We don’t have the technological knowledge to rehabilitate this tank,” said R. Kapuruhami, head of the farmers association at Selesthimaduwa in Anuradhapura District, North Central Province. “A politician promised to rehabilitate it for us, together with a private company, and we even spent money from our village farmers association, for the initiating ceremony. Then they excavated a few parts of the tank and took the silt, and we have not heard from them since. The tank is in the same state as it was before. This was my initiative, and now my fellow villagers blame me for the outcome. We need to have a permanent water supply, especially during the dry season. We do not have other sources of water, and there is no other way to cultivate our land. Because of this, our children are migrating to look for more stable jobs.”
Kapuruhami’s concerns echo those of many farmers in the region, whom IWMI researchers have interviewed during their field visits. A well-managed tank cascade system would enable more of these farmers to grow cash crops during the dry season. For this purpose, the project will upgrade village irrigation systems, in the hope of empowering smallholder farmers to adopt more climate-resilient farming practices. The project’s ultimate goal is to strengthen food, livelihood and water security through improved irrigation practices and drinking water management in the three river basins.