Assessing the Impacts of Land Use and Land Cover Changes on Sediment Yield Using the SWAT Model: A Case Study in the Khlong Bang Yai Watershed, Phuket Island, Thailand

Abstract

Land use and land cover (LULC) changes are among the most significant landscape transformations globally, reflecting the dynamic interaction between human activities and Earth’s surface processes. Phuket Island, Thailand, exemplifies a region experiencing rapid LULC changes driven by tourism and economic growth, with notable impacts on sediment yield. This study aimed to assess and quantify the LULC changes within the Khlong Bang Yai watershed, Phuket Island, estimate sediment yield, and evaluate the impacts of LULC changes on sediment yield. LULC data from 2002 and 2019 were analyzed using a post-classification comparison approach. A Digital Elevation Model (DEM), stream network, slope, soil, and daily weather data were used to parameterize the SWAT model, which estimated sediment yield under dry (2018–2019) and wet (2016–2017) conditions. Results showed urban and built-up areas expanded from 22.71% in 2002 to 36.71% in 2019, while evergreen forest declined from 25.85% to 21.10%. Sediment yield increased by 16% under dry conditions and by 638% under wet conditions, especially in subwatersheds where evergreen forest was converted to perennial trees and orchards and urban and built-up area. The SWAT model showed strong performance (NSE = 0.75–0.84, RSR = 0.4–0.5, PBIAS < 20%). Correlation analysis indicated negative relationships between evergreen forest and sediment yield (r = –0.409 dry; –0.739 wet), and positive correlations with perennial trees and orchards (r = 0.744 dry; 0.845 wet). Urban and built-up area showed strong negative correlations in low-elevation zones (r = –0.972 dry; –0.868 wet). These findings highlight the role of LULC changes in influencing runoff-driven sediment processes. The results support targeted strategies such as reforestation to address forest loss, riparian buffers and sediment basins for erosion control, slope stabilization in uplands, and improved drainage and zoning to reduce flooding, promoting watershed sustainability in Phuket’s rapidly urbanizing and environmentally sensitive landscape.