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Special Topic : Our Life, Our Water


Questions for Climate Science from 
the Mahaweli Water Managers


Dr. Lareef, originally from Sri Lanka, is a researcher of the International Research Institute for Climate Prediction in New York. He stayed at the FRSGC as a visiting researcher for three months. He will introduce the current problem Sri Lanka government is facing regarding the dam construction and the need of the climate modeling research in the future.


Lareef ZUBAIR ( Visiting Scientist, Climate Variations Research Program, FRSGC, and Researcher, International Research Institute for Climate Prediction, New York, USA )



The government of Sri Lanka has a decision to make. Sri Lanka generates 60% of electricity from hydropower, which is cheaper than oil or coal. It would like to maximize its hydropower generation by constructing an additional dam on the Mahaweli River. There are two potential sites near Talawakelle; one has greater hydro-electricity potential (125 MW) but greater financial and environmental costs than the other site, which has a smaller generation potential (90MW) but has
also less social and environmental costs. The suitable choice would have to be based on a careful assessment of costs, benefits and risks. This project is to be financed with a loan from the Government of Japan.
The Mahaweli is the longest river in Sri Lanka and it carries water from the so-called Wet Zone where water is plentiful to the Dry Zone. A reservoir was built at Victoria for irrigation and hydropower generation in 1985.



Viability of new dams is tradition-ally assessed based on historical stream flow and rainfall records. Now the consensus of scientific opinion is that global warming is indeed happening. Such warming is also evident in Sri Lanka. Many residents and water managers feel that there is less water in the springs and in the stream. The existing reservoirs constructed on the basis of historical stream flow have only filled up three times in two decades. Indeed, while there are large year-to-year fluctuations, the stream flow in the Mahaweli is indeed declining.


But is this decline due to deforestation, siltation, environmental degradation, construction of reservoirs or to climate change? These are questions that need immediate answers. Indeed, the rainfall too declines so that climate change is indeed at play here. But the water managers still have many questions. Will the trends continue? Is it reversible? Will the frequency of floods and drought change? What is the role of El Nino and such climatic variability? Will there be decadal variations?

These questions are examples of the challenges that climate change poses to policy makers, water managers, farmers and ordinary people. The traditional approach to water resources planning is based on a stable climate. Now, the methods used to optimize risk is not valid. The guidelines used for operating reservoirs are suspect. Indeed, one cannot act based on our past history anymore.


These are such questions that researches such as at Frontier Research System for Global Change can answer. A particular difficulty in using contemporary climate modeling work is the need to interpret from the 250-km scale of global models to what happens at a few kilometer scales in the Mahaweli basin. For example, Sri Lanka is only 270-km wide and 400-km long and is covered by only 4 grid boxes in contemporary global climate models. The climate however varies drastically within these boxes. Hence research from the high-resolution work of the Earth Simulator (where Sri Lanka would be covered by 700 grid boxes), will be particularly useful.

Victoria Reservoir

The Victoria reservoir and powerhouse on the Mahaweli river has the largest hydro-electricity capacity in Sri Lanka. The picture on the left is the Victoria when it was full in late 1980's. Over the last 50 years, the stream flow into the Victoria has declined by 40% and rain-fall has declined by 30%. Much of Victoria's capacity cannot be used as was the case during the last year (photograph on the right).

Looking from the Mahaweli river basin, one sees concretely that the water managers are severely challenged by climate change and climate variability. Understanding climate and environment at sufficiently small scales is necessary to understand hydrological variability and change that matters to the society at large. Along with development in climate and hydrological sciences, a paradigm shift in water resources design, and management and policy formulation is required to harness our ability to predict environmental variability and to adapt to a changing climate. But all these changes are yet to come; so Sri Lanka decided to build the larger dam this year.

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