Institute of Technology
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Item ASSESSING THE EFFECT OF LAND USE LAND COVER CHANGE ON STREAM FLOW AND SEDIMENT YIELD: THE CASE OF ROBIGUMERO WATERSHED, UPPER BLUE NILE BASIN, ETHIOPIA(Hawassa University, 2024-07-26) KASAHUN TADESSE MARELand use and land cover change significantly affected global water yield and sediment yield. The population within the Robigumero watershed experiences periodic increases that are attributable to changes in land use and land cover patterns occurring over both a spatial and temporal scale. Therefore, this study mainly focused on assessing LULC change and analyzing its impact on stream flow and sediment yield in the Robigumero watershed. For this study, spatial and hydro-meteorological data were used as model input. ERDAS Image 2015 was used to assess land cover classification and accuracy. SWAT model was used to simulate stream flow and sediment yield in monthly time steps. The model predicted stream flow with R2 values of 0.89 and 0.77, NSE values of 0.87 and 0.76, and PBIAS values of -2.3 and -5.1 during calibration and validation periods, respectively. Similarly, the model predicted sediment yield with R2 values of 0.80 and 0.75, NSE values of 0.80 and 0.74, and PBIAS values of -7.1 and 0..9 during the calibration and validation periods, respectively. During the study period from 1994 to 2021, the Robigumero watershed experienced substantial LULC change, with agricultural land and built-up area increasing by 18.6% and 160.8%, respectively, while forest, grassland, and shrubland cover decreased by 12.7%, 10.4%, and 40%, respectively. The calibrated model predicted results showed that on the watershed outlet point, mean annual stream flow increased by 4.64 m3 /s, and mean monthly stream flow increased by 0.86 m3 /s during the wet season and decreased by 0.14 m3 /s during the dry season from 1994 to 2021. Similarly, annual sediment yield increased by 5.5 t ha- 1 .yr-1 , with seasonal yields increasing by 4.84 t ha-1 .yr-1 during the wet season and 0.49 t ha- 1 .yr-1 during the dry season. Spatially, nine subbasins (43.3%) of the catchment revealed sediment yield-critical areas; from these, 24.02 t ha-1 yr-1 of sediment was generated. Implementing terracing, filter strips, and contouring in the critical subbasins demonstrated sediment yield reductions of 71.1%, 46.3%, and 51.9%, respectively. The findings of this study indicate that annual and wet season stream flow and sediment yield increased, while dry season stream flow was reduced. The change in stream flow and sediment yield is a direct result of the significant change in land use and land cover in the watershed. This suggests soil and water resource development in the catchment needs urgent regulation by the LULC and should be given priority to sediment reduction measuresItem Assessment of Climate Change Impact on Surface Water Availability: Gerhu-Sirnay Catchment, Mereb Sub- Basin,(Hawassa University, 2024-07-12) ZEGEYE TAMIRU HAMESSOInvestigating surface water availability under climate change impact is vital to ensure water resource sustainability. The general objective of this thesis was to assess the impact of climate change over surface water availability of Gerhu-Sirnay catchment using CORDEX-RCA4 with soil and water assessment tool (SWAT). To achieve this, quality of observed data was accepted for outlier, adequacy and consistency tests, and CORDEX-RCA4 datasets were passed the Power transformation and variance scaling bias correction and square root normalization. The baseline monthly stream flow (1990-2003) was modeled using SWAT, calibrated (1992-1999) and validated (2000-2003) in SWAT-CUP under SUFI2 tool. The CORDEX-RCA4 models were compared their performance at the baseline period (1990 to 2001) using volumetric metrics and Taylor diagram to predict future precipitation and stream flow variability by the best fit RCA4 model under RCP4.5 and 8.5 emission scenarios for 2050s and 2080s periods. The results showed that SWAT was very good at modeling baseline stream flow indicated by R 2 , NSE, PBIAS and RSR as 0.93, 0.94, 6.3% and 0.13 for calibration, and 0.82, 0.89, 10.4% and 0.07 for validation respectively. ICHEC-EC-EARTH-RCA4 was best fitted by scoring 0.9838, 0.0000, 0.9838 and 0.0162 for VHI, VFAR, VCSI and VMI respectively for volumetric, and 0.749, little less than 75 and little less than 100 for CC, NRMSE and δN respectively and better at annual scale at Taylor diagram. The baseline variability of seasonal rainfall indicated that an increments on the winter and autumn and decrease on the spring season. In the 2050s and 2080s of both emission scenarios significant increase and decrease was projected than the baseline periods at seasonal and annual scales. The mean annual rainfall was decreased by; 7.58% and 9.82% at 2050s and 2080s, and 4.92% and 9.28% during 2050s and 2080s under RCP4.5 and RCP8.5 respectively. The total change of rainfall was; 9.89% for 2050s and 13.52% for 2080s, and 8.79% at 2050s and 13.31% at 2080s for RCP4.5 and RCP8.5 scenarios respectively. Future annual stream flow will be decreased by; 8.84% in 2050s and 10.59% in 2080s, and 6.32% in 2050s and 9.88% at 2080s under RCP4.5 and RCP8.5 respectively. The total annual stream flow change will be; 9.88% during 2050s and 13.67% at 2080s, and 9.96% at 2050s and 13.86% at 2080s for the RCP4.5 and RCP8.5 scenarios respectively. Findings of this study indicated that climate change has significant impact over surface water availability of Gerhu-Sirnay catchment. To conduct policy oriented climate change impact over surface water availability, future researchers should consider multiple; climate variables, dynamic drivers and uncertainty analysis, and improve CORDEX inputs