Long-term soil moisture assessment using the optical trapezoid model for sustainable agriculture and environmental management in the western province of Sri Lanka

Abstract

The assessment of soil moisture plays a crucial role in various environmental and agricultural applications. This study conducts a thorough spatial analysis of soil moisture in Sri Lanka's Western Province from 2015 to 2024 using the OPtical TRApezoid Model (OPTRAM). Based on GeoTIFF images processed through Google Earth Engine and visualized in QGIS, the analysis revealed soil moisture values ranging from 0 (completely dry) to 1 (fully saturated). Significant temporal and spatial fluctuations were identified, with high soil moisture levels in Kalutara and Galle during 2015-2016, followed by a decline due to urbanization and land use changes in the subsequent years. By 2023, areas of low soil moisture had expanded across Colombo, Gampaha, Kalutara, and Galle. These results provide critical insights for water resource management and agricultural planning, illustrating the value of remote sensing in tracking long-term soil moisture dynamics.