WATER ALLOCATION FOR EXISTING AND FUTURE DEMANDS UNDER CHANGING CLIMATE CONDITION: CASE OF LOWER NYABARONGO CATCHMENT, RWANDA

Abstract

The main aim of this thesis is to study the current and future water availability and allocation under changing climate condition in Lower Nyabarongo river catchment in the developing country, where demands are growing and the supply seems to be constant. Assessment of impact of climate change on water resources in river catchment requires a proper estimation of availability of water and that can only be achieved by hydrologica modeling of the catchment. In this study a catchment simulation model (HEC-HMS) has been calibrated and validated for Lower Nyabarongo catchment for forecast of its hydrologic response. The future stream flow forecasted in the catchment were simulated by the dynamically downscaled RCP 4.5 (Representative Concentration Pathways scenarios has been adopted from CORDEX archive and bias correction were done by using power transformation equation before using in Hydrologic Engineering Cente Hydrologic Modeling system (HEC-HMS model). The annually result of current and future water availability from 1983-2010 and 2011 to 2040 in the catchment was found to be 7482.14Million Cubic Meter (MCM) and 5951.67Million Cubic Meter (MCM respectively. Water Evaluation and Planning System (WEAP) model is used for the study for wate allocation of the river water based on the existing water requirement and user priority setting situation. The water resources availability assessment and the allocations are performed for two scenarios; Scenario I: The current (1983-2010) water use rate. This scenario holds the overall existing water supply in Kigali, Muhanga, Gicumbi and Rwamagana city. Also two irrigation scheme and industry demand takes into account The overall irrigable area in this scenario is around 864.93ha. Scenario II: The presen water use rate plus various schemes under Planed. In this scenario the total irrigable area under this scenario is 5,000 ha. According to future scenario period the Kajevuba and Kanyenyomba irrigation projects shows increasing monthly water demand from 3.83 Million Cubic Meter to 64.57 Million Cubic Meter due to extension of the irrigation scheme. The Annually water demand and supplied for the current period found to be 78.49MCM while the demand rises to 244.10 MCM for the future scenario with unme demand of 165.61 Million Cubic Meter (67.87%)