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Assessment of Long-term Groundwater Abstraction and Forest Growth Impacts on Watershed Hydrology Using SWAT
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  • Wonjin Kim,
  • Jinuk Kim,
  • Soyoung Woo,
  • Jiwan Lee,
  • Sehoon Kim,
  • Seong Joon Kim
Wonjin Kim
Konkuk University
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Jinuk Kim
Konkuk University
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Soyoung Woo
Konkuk University
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Jiwan Lee
Konkuk University
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Sehoon Kim
Konkuk University
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Seong Joon Kim
Konkuk University
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Abstract

This study used Soil and Water Assessment Tool (SWAT) to investigate the impacts of groundwater abstraction and forest growth on the watershed hydrology of Geum River basin (9,645.5 km2), South Korea. Groundwater abstraction (GA) and forest growth (FG) data from 1976 to 2015 (1980s;1976~1985, 1990s; 1986~1995, 2000s; 1996~2005, 2010s;2006~2015) were prepared with 10-year interval as SWAT input data, respectively. SWAT was calibrated (2006~2015) using daily observation data from two multipurpose dams and three multifunction weirs. The dam and weir calibration result showed coefficient of determination (R2) of 0.78, 0.81, Nash-Sutcliffe efficiency (NSE) of 0.79, 0.76, root mean square error (RMSE) of 1.96 mm/day, 0.55 mm/day, and PBIAS of -5.48%, 8.56%, respectively. The SWAT ran at each decade using corresponding GA and FG information under the same weather condition of the 2010s to evaluate the impact of GA and FG on hydrologic cycle. Influenced by both GA and FG, the streamflow at the watershed outlet showed the decrease of 1.3% (10.1 mm/year), 4.4% (34.2 mm/year), and 7.8% (60.3 mm/year) in the 1990s, the 2000s, and the 2010s, respectively. The hydrologic response of surface runoff, lateral flow, groundwater flow, and soil moisture showed decreasing trend while evapotranspiration and groundwater recharge showed increasing trend. GA imposed bigger influence on the spatial and temporal loss of streamflow than FG. Especially, it was discovered that the agricultural water use from groundwater was the most influential factor that has decreased total runoff in the target watershed for the last four decades.