Evaluation of land use and land cover change impacts on stream flow: in Case of Temsa watershed, abbay river basin, Ethiopia, using soil and water assessment too

Abstract

The land use land cover were the major factors alters flow regime. Many studies evaluate impacts of land use land cover change on flow regime and understanding influence of it on river flow regimes was important for sustainable watershed management. An imbalance of natural resources due to human intervention brings an impact of one on another especially in developing countries. In the last 21 years Temsa watershed experienced land use/land cover change. The main objective of this study is to evaluate the Land Use change impacts on the stream flow of Temsa watershed. Specifically, the study analyzed the present land covers that have taken place in the watershed and its effect on the Stream flow responses of the watershed. Geographic Information system was integrated with the Soil and water assessment tool model to carry out the study. Arc GIS10.4.1 and ERDAS imagine2015 were used to process soil raster data set and prepare land use/cover map from Land sat image acquired in 1997 and 2018 respectively. Land use classification was performed using a supervised classification system and accuracy assessment was done using a confusion matrix. Using the two land use/cover map Soil and water assessment tool model was set up and run and the default simulation was compared with the observed data. Then sensitivity analysis was made on a monthly basis using 16 flow parameters whereas only five parameters were identified as influencing the flow. The model calibration was done from 1998 to 2010 and the validation period from 2011 to 2017. The calibration and validation results showed a good match of simulation with observation, with Nash-Sutcliff efficiency 0.73 & 0.82 coefficients of determination and 0.78 & 0.81 for calibration and validation respectively. The result showed that the mean wet monthly flow increased by 33.15% (from 30.166m3/s in1998 to 49.358m3/s in 2017), the mean short rain monthly flow increased by 9,086 %( from 15.023m3/sec in 1998 to 16.388m3/se in 2017) and the mean dry monthly flow decreased by 49.01% (from 16.2351m3/s in 1998 to 15.745m3/s in 2017). Generally, the study result indicated flow during wet season increased whereas during dry season decreased. The surface runoff contribution increased whereas ground water contribution decreased from 1997 to 2018 as a result of the expansion of agricultural and settlement areas. The study results showed a change in flow with change in land use/cover. The land use land cover changes scenarios were also developed by analyzing the impacts of land cover changes to the hydrological responses were modified or changed.