Simulation of Runoff Under the Past Impacts of Land Use Land Cover and Future Climate Change (Case Study of Anger Sub Basin)
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Date
2018-10
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Addis Ababa University
Abstract
Water resources are substantially affected by LULC and climate change. It was crucial to assess the impact of past LULC and future climate change on water resource. However, conflicting results on the effect of the LULC and climate change on runoff volume have been reported for Anger sub-basin which is located in East Wollega Zone of Oromia National Regional State (ONRS) of Ethiopia. ArcGIS was used to process preliminary data, extracting, layer stake, mosaic satellite images, and image classification. In addition to this Soil and Water Assessment Tool (SWAT) was adopted to perform runoff simulation. The good performance of the SWAT model was confirmed, with a Nash-Sutcliffe model efficiency coefficient (Ens) and determination coefficients (R2) of 0.76 and 0.90 respectively, for monthly runoff during calibration, and 0.63 and 0.84, respectively, during validation.
This study focused on assessing the past LULU and future climate change on runoff volume change. As research finding show that from the year 1986 to 2010, agricultural land increased by 39.3% and built up area increased by 0.5%. And also, shrub-land, forest area, and water body decreased by 32.9%, 6.6%, and 0.3% respectively during the study. The accuracy of LULC classification was achieved by overall accuracy, user’s accuracy, producer’s accuracy, and kappa coefficient.
Due to population growth, economic development and deforestation both maximum and minimum temperature increased differently during different scenarios. The temperature of this sub-basin increased by 0.52 Co, 0.68 Co, 0.40 Co, 1.74 Co, and 2.54Co, 3.04Co during the 2020s, 2050 and 2080 0respectively. On the other hand, precipitation of sub-basin decreased differently during different scenarios. It decreased by 2.06%, 7.63% and 17.67% during 2020s, 2050s and 2080s respectively.
From this study, it was observed that, due to urbanization, deforestation and agricultural expansion, past LULC change affect runoff volume of the sub-basin differently in different scenarios. The simulated runoff result indicated that runoff volume increased by 12.54Mm3 and 25.29 Mm3 between 1986-2000 LULC and 2000-2010 LULC respectively. And also due to future climate change, the runoff volume will decrease from baseline period (1990s) by 16.76Mm3, 44.96 Mm3 and 54.29 Mm3 during the 2020s, 2050s, and 2080s respectively.
Lastly, past LULC change affect water yield volume of the sub-basin differently in different scenarios. The simulated runoff result indicated that water yield volume decreased by 22.16Mm3 and 20.76Mm3 between 1986-2000 LULC and 2000-2010LULC respectively. And also due to future climate change the water yield volume will decrease from baseline period (1990s) by 14.50Mm3, 39.32 Mm3 and 78.85 Mm3 during the 2020s, 2050s and 2080s respectively.
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Keywords
SWAT, Arc GIS, Anger sub-basin, Land use land cover and climate change