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Lake Tana water balance assessment by the effect of climate change and land use interventions

Gebretsadik, Betelhem Wolderufael (2021) Lake Tana water balance assessment by the effect of climate change and land use interventions.

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Abstract:Lake Tana is the largest lake in Ethiopia, which is located in the upper Blue Nile Basin. The lake has a significant impact on society regarding income generation and food security since the community's livelihood around the lake depends on agriculture, fisheries, livestock production, and water transportation. In line with this, there are a number of water resource developments in the Lake Tana sub-basin, such as hydropower, large-scale irrigation, and water supply projects. Accordingly, the lake's sustainability is expected to be affected as a result of climate change and land use interventions. This study assesses the impact of climate change and land use interventions on the water balance of Lake Tana by using the water evaluation and planning (WEAP) model. The land use interventions this study focused on were the large-scale irrigation projects and dam constructions in the Lake Tana sub-basin. To assess the change in the lake's water balance, two time horizons were selected: baseline period (1991-2005) and future period (2041-2070). The water balance simulation of the WEAP was performed under four scenarios: baseline period (scenario 1), baseline period with land use interventions (scenario 2), future period (scenario 3), future period with land use interventions (scenario 4). Bias corrected ensemble mean of three dynamically downscaled RCM models under RCP4.5 and RCP8.5 emission scenarios were used for this study. The HBV rainfall-runoff model simulated streamflow from 19 catchments (gauged and ungauged). To estimate the irrigation demand of the 11 planned irrigation schemes, the AquaCrop model was used. The WEAP simulation result shows that the mean annual lake level of the baseline scenario is 1786.45 m.a.s.l. According to the WEAP simulation result, the mean annual lake water level of the baseline period under planned irrigation schemes and dam construction could decline by about 1.2 m when compared to scenario 1. The future period (scenario 3) revealed a mean annual lake water level decline of 0.51 m and 1.74 m for RC4.5 and RCP8.5 emission scenarios, respectively. The drop in water level under the RCP8.5 emission scenario is more significant than the RCP4.5 due to lower lake precipitation and higher open water evaporation because of increasing temperature for the RCP8.5 emission scenario compared to the RCP4.5 scenario. The mean annual water level under the combined effect of climate change and land use intervention will likely result in a decline of 2.78 m and 5.16 m water levels under RCP4.5 and RCP8.5 emission scenarios, respectively. According to the result, the combined impact of future development and climate change is more significant than the climate change impact. Evaluation of the sustainable water supply to the planned irrigation schemes was performed under the full implementation of the water resource developments. Findings indicate that for scenario 2, the irrigation schemes' unmet water demand is 19.4% of total water demand. WEAP results indicate that the unmet demand under scenario 4 is 11.4% and 20.5 % under the RCP4.5 and RCP8.5 scenarios, respectively. The unmet demand of the environmental flow requirement showed that the unmet demand is less than 1% for scenario 2 and RCP4.5 under scenario 4. While the unmet demand for the environmental flow requirement of scenario 4 of the RCP8.5 is around 4%.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
Link to this item:https://purl.utwente.nl/essays/88998
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