Climate and Water Resources

Water Resources has an intimate link with climate via the hydrological cycle. Yet, until a few years back, water managers have made little use of the predictability of climate and the understanding of variability. We explored the usability of climate information and predictions for water resource and river basin management.

Partners Status Next Steps
Seasonal Climate Information for Water and Environmental Management in the Mahaweli Basin

(1) to identify necessary climate forecasts and information

(2) to develop hydro-climatic models and analytical tools

(3) to generate a framework to support decision-making

The Mahaweli Authority, Department of Irrigation, Interim National Water Resources Authority of Sri Lanka.
Supported the formation of a National Steering Committee on Seasonal Climate Predictions and Applications (NASCOM), provided climate information and forecasts, Research Paper on decadal changes of hydro-climatology in Sri Lanka under review.
Continued dissemination of climate information.
Land Surface Modeling
Relate meteorological model output into land surface propertie
Sarith Mahanama, NASA Global Modeling and Assimilation Office, Greenbelt.
Land Surface models implemented and meteorological forcings refined for producing high-fidelity stream flow for Sri Lanka.
mplementation of model at IRI and at FECT. Publications

Training of Mahaweli Engineers
To build technical capacity in climate analysis and hydro meteorological analysis techniques
Mahaweli Authority River Basin and Head works Divisions
Engineers Badra Nawaratne and Udayangani Palagama obtained training for two weeks at Polgolla. Since December, Engineer Badra Nawaratne commenced work full time.
Review of climate related design methods, hydro meteorological information systems.


Climate Information for WRM

It is illuminating to separate the climate inputs into water resources management (WRM) into the seasonal to inter-annual and longer term components. The seasonal component bears on operation of reservoirs and diversion points and seasonal management. The longer-term climate bears on water resources planning, the prediction of extremes and policy issues. The differences are captured in the following sketch diagram.

Project Setting

King Prackrama
Parakrama Bahu, King of Sihaladvipa (1153-1186)

In my kingdom are many paddy fields cultivated by means of water, but few indeed are those which are cultivated by means of perennial streams and great tanks. By rock, and by many thick forests, by great marshes is the land covered. In such a country, let not even a small quantity of water obtained by rain, go to the sea, without benefiting people.


In January 2000, we initiated a project to apply climate information and prediction for river basin management in the Mahaweli basin in Sri Lanka. The Mahaweli Authority is responsible for river basin management in the Mahaweli and adjacent rivers. This river basin provides half of Sri Lanka’s electricity requirements, rice and tea production respectively. Climate information has entered into basin management in terms of historical statistics. Recently, however monitored climate information and seasonal climate predictions have become available. Such timely information provide an opportunity for adaptive basin management. The following were key steps:

  • Characterization of climatology, climate variability and secular trends within the river
    basin. Strong spatial variability is evident.
  • Evaluation of predictability of in-situ rainfall and stream flow using global sea surface temperatures was undertaken and significant predictability was found.
  • Development of localized rainfall predictions based on Global Climate Models
  • Simulations using “downscaling” techniques resulting in predictions at a high resolution.
  • Study of climate impacts on key sectors in the Mahaweli basin such as rice, tea, hydro-electricity, water supply, human-elephant conflict and malaria established high vulnerability to climatic anomalies.
  • A study of climate information needs was carried out. Climate information and
    predictions is needed particularly at the start of the planting season in September and March.
  • Capacity building for climatic analysis within Sri Lanka.

The River Basin setting

The 207 misri Lankale long Mahaweli river traverses from the so-called "Wet Zone" of the island to the "Dry Zone“. Of the annual precipitation in the basin of 28,000 MCM, 9,000 MCM is discharged to the sea. Its catchment spans 10,448 square km and feeds 1003 tanks. Water transfer has been augmented with dams, canals and tunnels during rapid development from 1978 onwards under the Accelerated Mahaweli Project. The Mahaweli project involves the generation of hydroelectricity, irrigation of the "Dry Zone", land settlement, employment generation and infrastructure development. There are four reservoirs in the main trunk of the river with a storage capacity of 1,500 MCM and there is a bigger storage capacity from trans-basin diversions. This project led to hydropower generation capacity of 470 MW and irrigation of an additional 365,000 ha of land in the Dry Zone. There are competing demands for water for irrigated agriculture in different areas, for hydro-electricity, for river and watershed ecology, for public health and for social welfare. The need for water for irrigation and domestic use is particularly acute in the downstream. Agricultural production in the dry zone varies dramatically with the availability of water. Drought has brought on scheduled power cuts in the national grid.


Water Management in the Mahaweli River Basin

Rice or Paddy is the principal subsistence crop and it needs large amounts of water. Rice cultivation is carried out in the main Maha season from October to March and in the subsidiary Yala season from April to September. Both seasons begin with the rainfall in September-October and April-May. However, the monsoon system results in higher rainfall in the Maha season and lower rainfall in the Yala season. There is high rainfall due to orographic influence in the South-West quadrant of the island in Yala. Hence rivers such as Mahaweli and Walawe which originate in the South-West and traverse elsewhere are important sources of irrigation during Yala.

Climate Predictions needed for Seasonal Decision-Making

An elaborate system of water management is in place. Water management is based on consultation at various geographic scales: that of the field, block, system, basin and island-wide. Climate information is needed weekly for system operation, seasonally for seasonal planning and in the long-term for infrastructure development and policy. Here are the seasonal intervention points.

  • In September, decisions as to extent of rice cultivated for Maha cultivation season is decided based on water in storage, consultations with farmers. Short-term, 3-6 months climate predictions needed
  • In April, Decisions as to extent of rice cultivated for Yala cultivation season is decided based on water in storage, consultations of farmers and irrigation managers. Short-term, 3-6 months climate predictions needed
  • Around January, Energy Managers need 3-9 months prediction to determine whether reservoir storage is sufficient to meet hydro-electricity demands till October rains.


We have already found:

  • Evidence for vulnerability to climate variability and climate change
  • Evidence of climate sensitivity of water supply, rice and hydro-electricity production.
  • Significant predictability for in-situ variables in the Mahaweli river basin.
  • Climate information is needed at the start of the planting season in September and March and during the start of the dry spells in January and June.
  • Climate variability, climate change and land use change needs to be considered in analyses.
  • Climate information needs are multifaceted and vary from one management situation to another.
  • Our work has provided a proof-of-concept that seasonal climate information can be profitably introduced for basin management in a typical tropical setting. Work is ongoing towards a comprehensive project.


  • December 2005: Lareef Zubair and Janaki Chandimala, Epochal Changes in ENSO-Stream flow relations in Sri Lanka, in press, Journal of Hydrometeorology.
  • October 2005: Janaki Chandimala and Lareef Zubair, ENSO based Stream Flow and Rainfall Predictions for Water Resources Management in Sri Lanka, in revision, Journal of Hydrology.
  • November 2004: Janaki Chandimala and Lareef Zubair, Predictability of Stream flow and Rainfall in the Kelani river basin in Sri Lanka using ENSO, International Conference on Sustainable Water Resources Management in the Changing Environment of the Monsoon Region, United Nations University, Colombo, Sri Lanka Nov 2004: May 2003 disaster in Sri Lanka and Cyclone 01-B in the Bay of Bengal, Natural Hazards, 33: 303-318, 2004.
  • September 2003: Lareef Zubair, Sensitivity of Kelani Stream flow in Sri Lanka to ENSO, Hydrological Processes. 17 (12) 2439-2448.
  • Aug 2003: What led to the May Flooding, The Island, Sri Lanka, August 23, 2003.
  • June 2003: Lareef Zubair, Ruvini Perera and Herath Mathrithillake, Using Climate Information for Mahaweli river basin management, World Water and Environmental Resources Congress 2003, Philadelphia.
  • January 2003: Lareef Zubair, ENSO influences on Mahaweli Stream flow in Sri Lanka, International Journal of Climatology. 23(1)91-102
  • October 2001: Seasonal stream flow predictions from sea surface temperatures: Application to Mahaweli river in Sri Lanka, National Oceanic and Atmospheric Agency 26th Climate Diagnostics Workshop, San Diego, California.
  • Nov 1999: Modelling of Irrigation Networks: Udawalawe in Sri Lanka, Jubilee Congress of the Asian Institute for Technology, Bangkok, Thailand, 1999, IV: 91-100, with R. Aloysius.


  • 2005: Janaki Chandimala and Lareef Zubair, FECT Technical Report-6, Construction of rainfall indexes for the Kelani Catchment.
  • July 2002: Lareef Zubair, Questions for Climate Science from Mahaweli Water Managers, Frontier Newsletter, Japan


  • January 2006: Advances in Climate Sciences for Mahaweli River Basin Management, Head works Divisions, Mahaweli Authority, Digana.
  • November 2005: Predictability of Climate around Sri Lanka and its Applications, Global Modeling and Assimilation Office, National Aeronautical and Space Agency, Greenbelt, Maryland.
  • November 2004: Climate Information for Mahaweli River Basin Management, Head works Divisions, Mahaweli Authority, Digana.
  • December 2003: Workshop on the Climate of Sri Lanka and Climate Applications for staff of the Headworks division of the Mahaweli Authority and the Central Engineering Consultancy Bureau at Digana, Sri Lanka,
  • March 2003: Applications of Seasonal Climate Predictions, National Water Resources Authority (Interim), Colombo.
  • January 2003: Climate Prediction for Water Resources Management in Sri Lanka, Office of the Minister of Water Resources and Irrigation, Colombo.
  • January 2003: Seasonal Climate Predictions and its Applications in Sri Lanka, International Water Management Institute, Colombo.
  • December 2002: Climate Predictions for Mahaweli River Basin Management, Mahaweli Authority of Sri Lanka, Colombo, Sri Lanka.
  • July 2002: Review of IRI-MASL projects and plans for the future, Environment and Forestry Division, Mahaweli Authority of Sri Lanka.
  • May 2002: Climate Change, Climate Variability and Water Resources, School of Engineering, Tokyo University, Japan.
  • May 2002: Climate Change, Climate Variability and Water Resources, Frontier Research System for Global Change, Yokohama, Japan.
    October 2001: Seasonal stream flow predictions from sea surface temperatures, 26th Climate Diagnostics Workshop, San Diego, CA
  • March 2001: Sri Lanka Water Resources Project, International Scientific and Technical Advisory Committee of the International Research Institute, Palisades, New York.
  • January 2001: IRI Water Resources Applications Project in Sri Lanka, NOAA Office of Global Programs, Silver Spring, Maryland.
  • August 2000: Climate Prediction for Water Resources Management, International Water Management Institute, Colombo, Sri Lanka.
  • August 2000: Climate and its Prediction in the Mahaweli Basin, Environment and Forest Conservation Division, Mahaweli Authority of Sri Lanka, Sri Lanka.
  • August 2000: Climate Prediction for the Mahaweli, Water Management Secretariat, Mahaweli Authority of Sri Lanka, Sri Lanka.
  • August 2000: Climate Prediction for Water Management, Department of Irrigation, Colombo, Sri Lanka.