Impact of water availability scenarios on present and future water allocation options in Rwizi catchment, Uganda

Abstract

Equitable and participatory water allocation to meet the competing water needs of users has always been a challenge for regulators in river catchments the world over. Rwizi upper catchment is water stressed with domestic, agricultural and industrial water demands. Supply and demand management is usually aimed at managing unmet demand. However, this has continued to be a big challenge in Rwizi catchment amidst competition for the available water resources and lack of a water allocation tool that recognizes stakeholder’s priorities while embracing equity. As such, the main objective of the study was to evaluate the impact of water availability scenarios on present and future water allocation options in Rwizi upper catchment. The specific objectives included: characterization of the Rwizi catchment, assessment of water availability scenarios and developing a decision support mobile application to aid participatory allocation of water under various water availability scenarios. The scenarios considered in this study included “business as usual” which considers continued social economic patterns, “adaptation” which considers implementation of water saving regulations, “worst case climate” and “likely future scenario” which considers anticipated climate and social economic trends. The Arc Hydro model was used to analyze the hydrological characteristics of the catchment. Assessment of water availability scenarios was undertaken using the WEAP model. Developing water allocation support tool was then done using questionnaires for stakeholder focus group discussions to collect prioritization and weighting data to identify water usage priorities and set up a decision support tool in form of an App. The results of the study showed that allocating water using the “Adaptation” scenario presented the highest positive impact on demand as it yielded a reduced unmet demand of 0.012 MCM/year. This is better than the “Business as Usual” and “Worst Case Climate” Scenarios which resulted in unmet demands of 647,433 MCM and 12,109,897 MCM respectively. The most desired option of allocating water to domestic users first will be feasible if the allocation takes the course of adaptation scenario. In conclusion, regardless of the allocation option and scenario chosen, there will still be unmet water demand. The use of a MCDA tool is a good and rational process of arriving at water allocation decisions and this study designed and digitized such a tool. It further demonstrates the possibility of developing a simple decision support tool in form of an App that can be used by stakeholders in a small water stressed catchment.