Impact of Land Use and Land Cover Change on Hydrological Processes of the Upper Awash Sub-Basin, the case of Melka Hombole watershed, Ethiopia
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Date
2020-06
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Addis Ababa University
Abstract
The increase in comprehensive socio-economic activities have resulted in considerable changes
in the land use and land covers of Melka hombole watershed of the Upper Awash sub-basin of
Ethiopia for the last years. This study examines, thus, the changes in hydrological processes in
response to changes in land use and land covers during the period 1995-2015 by integrating
remote sensing, GIS and Hydrological modeling. Land use land cover classifications for 1995,
2005, and 2015 were conducted by employing supervised approach of classification image. The
accuracy assessment result revealed that the overall accuracy of 87.71% was achieved for the
current image classification. Kappa coefficient was found 0.97. Post classification comparison
technique was applied to detect the changes in land use land cover. The LULC change analysis
revealed that the cultivated land, urban and water body have increased by 14.23%, 3.05% and
0.12% respectively and that of grass land, woody vegetation, wetland and bare lands decreased
by 9.15%, 8.34%, 0.06% and 0.04% respectively during the study period of 1995-2015. The
three generated land cover maps were, then, used to run the Arc SWAT model so as to evaluate
the impacts of the detected land use and land cover changes on the stream flow. Sensitivity
analysis, calibration, and validation of the model simulation were conducted and 12 parameters
were identified to be sensitive for the stream flow and were used for further model calibration
and validation. Calibration was executed using the observed stream flow data of Hombole
gauging station from 1998 to 2007 leaving 3 years of warm up period. Consequently, validation
was undertaken from 2008 to 2015. Both the calibration and validation results revealed a good
match between measured and simulated stream flow expressed by a coefficient of determination
(R2
) of 0.82 and that of Nash-Sutcliffe Efficiency (ENS) value of 0.81 for the calibration, and a
value of 0.76 and 0.75 for the validation period respectively. Then the model was run to obtain
the values of surface runoff and ground water return flows for the three respective time periods.
The result indicated that the mean monthly stream flow for wet season has increased by 19.63%
and has decreased 30.74% for dry months. Total water yield of the watershed has increased by
21.67%. Generally, surface runoff has increased by 38.69% while lateral flow decreased by
21.82% during the study period owing to the increase of cultivated and urban lands and decrease
of vegetation cover. The annual actual evapo-transpiration has decreased by 16.34% from 1995
to 2015. Therefore, the results confirmed that the hydrological processes of the study area have
changed due to land use and cover changes undertaken in the past two decades.