Abstract:
Globally, there has been a lot of research on land use/land cover (LULC) change, which
has profound effects on both natural and human systems. In this study, Weyib watershed
historical LULC changes, as well as their impacts on stream flow was assessed using Soil
and Water Assessment Tool (SWAT). Spatial data (Digital Elevation Model (DEM), Soil
Maps, Landsat images) and Hydro-meteorological data (Stream flow and Weather data)
were input data used in this study. The DEM, soil map, and LULC map of the watershed
were prepared by using Arc Geographic Information System (ArcGIS) 10.4.1 software.
The LULC classification and its accuracy assessment were carried out by using Earth
Resources Data Analysis System (ERDAS) imagine 2015. The investigation of changes in
LULC within the watershed was implemented using satellite images (2002 and 2020).
The LULC classification results indicated that, the expansion of agricultural land by
11.54% and urban areas by 3.73%. Grassland, water bodies, forests and shrub land were
decreased by 6.83%, 1.09%, 2.45% and 4.98% respectively due to socioeconomic
development, population growth and pressures for agricultural land needs. Using the two
years (2002 and 2020) LULC maps for hydrological simulation, the SWAT model was set
up and run. Then, sensitivity analysis was completed on a monthly basis using 15 flow
parameters and only 8 parameters were identified as influencing the stream flow. The
model calibration and validation were done from 1992 to 2002 and from 2003 to 2008
respectively and the simulation was compared with the observed data. The result showed
a good match of simulation with observation with coefficient of determination (R2
) 0.94
and 0.98 and Nash-Sutcliff efficiency (NSE) 0.69 and 0.72 for calibration and validation
respectively. The mean wet monthly stream flow increased by 37.49% (from 31.66m3
/s in
2002 to 43.53m3
/s in 2020) and the mean dry monthly stream flow decreased by 31.10%
(from 18.10m
3
/s in 2002 to 12.31m
3
/s in 2020). Generally, the study result indicated
stream flow during the wet season increased whereas during the dry season decreased
because of increment of agricultural and urban area, and reduction in forest, shrub land,
water body and grassland result on variation of surface runoff and ground water flow.
