Abstract:
Soil erosion is one of the most important environmental concerns faced by the world
today, and it seriously compromised the fate of human societies and the achievement
of sustainable development goals that ensure human and environmental well-being.
Numerous factors affect soil erosion, while human-induced changes in climate (rainfall
and temperature) and land use land cover (LULC) changes are the most important
driving forces. Assessing soil erosion and understanding the impacts of climate variables
and LULC changes on soil erosion are crucial for the watershed management. Thus,
this study used the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST
3.9.2) Sediment Delivery Ratio (SDR) model which was introduced by the National
Capital (NatCap) Project in collaboration with the Stanford University – USA to
assess soil erosion in the Samanalawewa watershed (SW), in Sri Lanka and its eight subwatersheds,
over 20 years (2000-2020) with five-year time intervals. Further, the Pearson
correlation test was used to establish the relationships between climate variables, LULC
changes, and soil erosion of the SW watershed. The estimated mean annual soil erosion
rates were 53.2, 52.9, 69.7, 87.7, and 70.2 t ha−1year−1 for the years 2000, 2005, 2010,
2015, and 2020 respectively. Estimated soil loss values of the SW are 10 to 18 times
greater than the soil erosion tolerance (5 t ha−1year−1) in Sri Lanka. Correlation analysis
disclosed that there is a significant correlation (p<0.05) between soil erosion and two
driving forces viz. temperature and LULC changes (mean annual temperature and forest
cover in the watershed has slightly increased over time). These results would help in
formulating watershed management policies and the implementation of proper soil and
water conservation measures in the watershed.
