Climate and Water Resources

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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.

Activity
Objectives
 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.

 

  1. Seasonal Stream Flow Predictions

  2. Streamflow Prediction based on ENSO

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

“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.”
- Parakrama Bahu, King of Sihaladvipa (1153-1186

 

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:

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.

Summary

We have already found:

Outputs

Reports

Presentations