Abstract:
Land use land cover change is the global phenomenon that affects the watershed
hydrological process and subject to changes causing the area to form impervious surface
that affects the hydrological processes. This study was conducted to investigate the impact of
land use land cover changes on hydrology of Upper Gilo Watershed located in the Baro
Akobo River basin, southwest of Ethiopia. In this study SWAT model was selected as it
applies distributed at required scale. Land use/Land Cover data, Hydrological data (stream
flow) and meteorological data were obtained from Ethiopian Map Agency, Ministry of water
Resources, Irrigation, and Electricity, National meteorological Service Agency respectively..
The result of sensitivity analysis has shown that the curve number (CN2), GWQMN, CH_K2,
ALPHA_BF and SOL_Z are the top most sensitive parameters. The model was calibrated
using stream flow data from 1993 to 2006 and validated from 2007 to 2014. The R2
and NSE
values were used to examine model performance and the result indicates 0.91 and 0.82 to R2
and 0.77 and 0.61 to NSE during calibration and validation respectively. The classified Land
use map of 1995, 2004 and 2013 which were obtained from Ethiopian Mapping Agency
indicate that the cultivated land and settlement have expanded during the study period of
1995-2013 by 14% and 7% respectively and unlike that, forest and grass land were
decreased by 11% and 4.7% respectively during the period. The effects of the land use land
cover changes (1995-2013) have impacted on the stream flow of the watershed that changes
the magnitude of surface runoff and sediment loading increased by 22% and 84%
respectively but lateral flow, ground water flow, Aquifer recharge, and percolation capacity
of the soil was decreased by 3.4%, 12.9% 8.4% and 14.6% respectively. During the study
period, maximum annual surface runoff was contributed by sub-basin 31, 5 and 28 and the
highest ground water was contributed by sub-basin 29, 25 and 25 for the period of 1995,
2004 and 2013 respectively. And maximum sediment load is contributed by sub-basin 22, 19
and 27.
