Abstract:
To optimize benefits of the ongoing and planned water resources developments for sustainable socio
economic development in Tana and Beles sub-basin, Ethiopia, an integrated adaptive water
resources management system is crucial. The objective of this study is to provide inputs to adaptive
water management by evaluating the impact of ongoing and planned water resources developments
with and without climate change on performance of Beles hydropower and main irrigation projects in
Tana-Beles sub-basins. This study is different from previous studies for the study area since high
resolution climate data and new climate scenario are used. Two independent water resources
scenarios were evaluated. Scenario I refers to implementation of the water resources development
projects without climate change, i.e. using historical climate data. Scenario II refers to
implementation of the water resources development projects under climate change for three future
periods: near term (2011-2040), medium term (2041-2070) and long-term (2071-2095) with a
baseline scenario (1971-2000). Dynamically downscaled climate model outputs were obtained from
CORDEX-Africa program for the Representative Concentration Pathway of RCP4.5.The climate data
was bias corrected before serving as input to the impact models. The HBV-96 rainfall-runoff model
was used to simulate inflow of Lake Tana while WEAP21 was applied to assess the performance of
the water resources projects. Under Scenario-I (without climate change), the reliability of
hydropower production reaches 83% with 100% demand coverage while there is considerable unmet
irrigation water demand. Under Scenario-II (with climate change), water resources availability
(inflow to Lake Tana, net basin supply and lake storage level) of all future scenarios will likely
increased unlike medium term scenario inhabited with insignificant change. Medium-term scenario
will face a considerable unmet demand of Tana sub-basin irrigation projects and Beles hydropower
reliability of 76%. This will be promoted in the near and long-term scenario with reliability of Beles
hydropower by 90% and 91.7% respectively. The most likely affected major irrigation projects by
climate change are Jema and Megech followed by Ribb, Gumara, Koga and Tana pump irrigation
sites. The two independent scenarios were evaluated without affecting standard minimum operation
of the lake safe for navigation and downstream environmental flow requirement. For both scenarios
(with and without climate change) the maximum unmet demand for Beles hydropower will be 4.5%
and 13% respectively showing that impact of water resources development on Hydropower is
insignificant.
