EVALUATION OF THE COMBINED IMPACT OF CLIMATE CHANGE AND FUTURE WATER ABSTRACTION ON LAKE ZIWAY WATER BALANCE, CENTRAL ETHIOPIA

Abstract

Climate change and continued human activities posed a threat to the water balance of Lake Ziway in central Ethiopia. However, there were very limited studies that addressed the combined effect of climate change and water abstraction for agriculture on the water balance of the lake. In this study, considered the combined impacts of climate change and water abstraction on the Lake Ziway based on high-resolution data from multiple GCM climate models and the Representative Concentration Pathway (RCP) scenarios. Climate change was evaluated for two time periods: 2021-2050 and 2051-2080 considering the baseline period of 1971-2000. The power transformation approach was applied to correct the remote sensing precipitation data while the variance scaling method was employed for temperature correction. The IHMS hydrological model was used to simulate surface inflow into the lake. The model was calibrated and validated using the 1985-1999 and 2000-2007 streamflow data periods, respectively. The CROPWAT 8.0 model was used to estimate the irrigation water requirements of the major crops grown in the study area. The IHMS model performed well and can be suited for the prediction of water balance components. The minimum and maximum temperatures show an increasing pattern for both future periods. The existing crop water requirement was computed as 41.9 Mm3 per year from 1980-2009. The effects of water abstraction resulted in the reduction of maximum mean annual lake volume by 257.2 Mm3 per year from 2051-2080, and a 77.5 cm drop in lake level with 25 km2 surface area reduction. The annual maximum raise of lake Ziway water level will be likely 0.624 m due to climate change. The combined effect of climate change and water use may result in a drop in the lake level by some order of 25 cm with 10 km2 surface area and 101 Mm3 volume reductions, respectively, annually. Therefore, the introduction of cautionary measures, proper planning, and monitoring for lake water use in the future are recommended.