Abstract:
Assessment of the current climate change impacts on water resource availability and its utilization
should be made to account in future water resource development works and its operational
management. Meki-Ziway watershed, found on the northern part of Central Rift Valley, is an area
of an active part in water resource development activities particularly irrigated agriculture around
the Lake and on its tributaries. The availability and use of water on the Lake system is an issue of
very sensitive because of great socio-economic activities, ecological values and climate change
impact. In the last 30years, the inflow from the two tributary rivers Meki & Katar are nearly 250
and 410MMC respectively in a decreasing trend. The outflow to Bulbula River is about 180MMC
which is important for ecological balance. The aim of this thesis is to evaluate the impact of climate
change (future change in precipitation and temperature) on water availability using ArcGIS and
HEC-HMS hydrologic model and its utilization assessment and allocation by Water Evaluation and
Planning (WEAP) model aiming to provide results for the water managers and policy makers.
Historical data and downscaled IPCC A1B scenario variables (precipitation & temperature) were
used as input to the HEC-HMS hydrologic model to simulate future stream flow changes in the
Meki and Katar Rivers and runoffs from the lake adjacent catchments. Hydrological model result of
the two rives showed increase flows by 13.71 and 12.42% in the future periods of 2009-2040 for
Meki and Katar Rivers respectively, the two tributary rivers, relative to historical period of 1981-
2008. The precipitation in the Lake watershed is increased by 13 and 2% in the scenario periods of
middle term 2009-2024 and long term 2025-2040 respectively. Irrigation requirement is increased
10% in average up to 2040 and evapotranspiration by 2-3% in the Lake watershed. In the same
periods the mean minimum and maximum temperature is raised in Katar and Ziway sub-catchments
0.2 and 1.2.0°C and 1.2 and 5.8°C in Meki River sub-catchment which is bigger relatively to other
sub-catchments.
Considering historical inflow and its deceasing trend, the result of WEAP model evaluation with
regulated the Lake level, result indicates the maximum optimal total annual abstraction was set to
be 98.618MMC with 90% reliability and 10.85MMC total unmet demand even if the future inflows
seems to meet all potential development plans.
