Abstract:
Land use and climate changes are among the biggest issues facing the world today. The
main purpose of this study was to assess the impact of land use and climate change on
Melka Wakena reservoir sedimentation by using Geospatial tools and Hydrological
models. Two time (1990 and 2016) land use land cover data and CORDEX-Africa data
outputs of HadGEM2-ES regional climate model were used for this study along with other
spatio-temporal data sets. T he data (1971-2000) was used for baseline scenario analysis.
Future scenario analysis was performed in two-time frames: near-term (2020-2049) and
mid-term (2050-2079) under selected representative concentration pathways (RCP4.5 and
RCP8.5) scenarios. After assessment of missing, quality and consistency of data, bias,
coefficient of variation and correlation were used to evaluate the systematic error of
precipitation amount, the degree of precipitation variability and bias-corrected before
serving as input to the impact analysis. Observed annual precipitation shows decreasing
trend, whereas temperature shows an increasing trend. Impact assessment on sediment
yield was done by Soil and Water Assessment Tool (SWAT) to simulate future sediment
load for the predicted climate variables. Model performance was evaluated using
coefficient of determination (R2), Nash-Sutcliffe Efficiency (NSE) and percent bias (PBIAS)
during calibration and validation. The result of calibration and validation of sediment yield
R2, NSE and PBIAS are 0.83, 0.79, 14.9 and 0.87, 0.82, 14.2 respectively. In this study the
SWAT model yields average annual sediment load of 1430,and 1790.45 ton/ha/yr come
into the Melka wakana Reservoir under LULC 1990, and 2016 respectively. The future
precipitation predicted a decrease ,while temperature was increased in all RCP4.5 and
RCP8.5 near and mid-term scenarios from the baseline period. These change in climate
variables are result in an increase in mean annual sediment yield of 1.65% and decreaseby 23.09 % for RCP4.5 scenario and decrease by 19.88% and 18.84 % for the RCP8.5
scenario for the near and mid-term respectively. Finally,from this study we observed that
the runoff and sediment yield of watershed show decreasing and increasing trends when
we compare future scenario and land use of (1990_ 2016) respectively .
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