Climate Scenario Identification and Evaluation of Irrigation Responses: Case Study Application of Rambakan Oya Reservoir Using Irrigation Department Guidelines

Present study was carried out to demonstrate the capability of Irrigation Department Guideline (IDG) model to assess climate change impacts under variety of scenarios by carrying out a case study of Rambakan oya irrigation scheme. The IDG model was optimized for the current irrigable area and verified by checking the irrigable area, spilling months, maximum and minimum storages with qualitative field assessments. Six climate change scenario were developed and three scenarios were identified as critical scenario after evaluating the possible impacts on cultivation extents. Critical scenario were incorporated in to the optimized model in order to evaluate the response and it was observed that a 30% decrease in north-east monsoon (December to February) and 30% increase in south-west monsoon (May to September) keeping the annual total constant would give rise to the highest impact. Annual irrigation demand of Ramabakan Oya reservoir increases by 3% and the cropping intensity reduces from 1.0 to 0.76 and 0.83 to 0.72 in maha and yala seasons respectively. Since cropping intensity of the Rambakan Oya could reduce up to 20% under future climate change scenario, it would be better to incorporate adaptation measures to execute water management plans in the future. Project efficiency enhancement of 7% will allow the present cropping intensity to be maintained under the worst-case scenario for Rambakan oya irrigation schem