Upstream Downstream Interaction and Impacts of Climate Change on Water Storage Interventions in the Abbay River Basin, Ethiopia

Abstract

In the planning and management of water resource systems comprising a large number of water reservoirs, it is necessary to simulate the interaction of entire systems rather than to consider the reservoirs separately. The Water Evaluation and Planning (WEAP) model is used to assess water demand and upstream downstream flow interaction of water storages by considering the existing development situation and future water resources development with and without climate change scenarios in the study area(Abbay River Basin, Ethiopia). Three different development and climate change scenarios were developed to simulate Water use at demand sites and flow interaction for 46-years period i .e., i) Current Condition Scenario (1995-2010) ; ii) Sho11 terrn development Scenario with and without Climate Change (2010-2025); and iii) Long term development Scenario with and without Climate Change (2025-2040). Twenty Large Dams/Reservoirs and/or twenty Seven large irrigation and hydropower projects (including dam projects) which can significantly affect the flow pattern were considered for the study. Irrigation Projects covering an area of 365,807 hectare of land and Hydropower projects which can develop 7,764MW Power have been selected from different sub-basins based on the basin Master Plan Study. The competing water sectors were irrigation development, hydropower production and environmental flow requirements. Next to environmental flow, high priority was given to hydropower projects than irrigation during the simulation. Net evaporation from reservoirs, River headflow, Monthly water demand and reservoirs physical and operation data were the basic inputs to the model. Penman-Monteith was used to estimate evaporation rate from 20 large reservoirs and reasonable results were model simulation results, there is a reduction of flow at the border for all different development and climate change scenarios. The current WEAP simulated flow at the Sudanese border was 47.08BCM per year. This flow will reduce to 46.48BCM and 45.22BCM for 2010-2025 and 2025-2040 development periods respectively. Considering Climate Change impacts on hydrology and reservoir systems, the mean annual streamflow is expected to be 46.00BCM for 20 I 0-2025 and 44.36BCM for 2025-2040 scenanos. In all scenarios and simulation periods water availability in the basin is far above the demand required i.e. , demand coverage and reliability of 100 was observed in the WEAP simulation result. Hence, unmet demands will not be the problem both for irrigation and hydropower production; keeping the minimum environmental flow to Tiss Issat fall.