Soil erosion risk in Korean watersheds, assessed using the revised universal soil loss equation

Soil erosion reduces crop productivity and water storage capacity, and, both directly and indirectly, causes water pollution. Loss of soil has become a problem worldwide, and as concerns about the environment grow, active research has begun regarding soil erosion and soil-preservation policies. This study analyzed the amount of soil loss in South Korea over a recent 20-year period and estimated future soil loss in 2020 using the revised universal soil loss equation (RUSLE). Digital elevation (DEM) data, detailed soil maps, and land cover maps were used as primary data, and geographic information system (GIS) and remote sensing (RS) techniques were applied to produce thematic maps, based on RUSLE factors. Using the frequency ratio (FR), analytic hierarchy process (AHP), and logistic regression (LR) approaches, land suitability index (LSI) maps were developed for 2020, considering the already established Environmental Conservation Value Assessment Map (ECVAM) for Korea. Assuming a similar urban growth trend and 10-, 50-, and 100-year rainfall frequencies, soil loss in 2020 was predicted by analyzing changes in the cover-management factor and rainfall–runoff erosivity factor. In the period 1985–2005, soil loss showed an increasing trend, from 17.1Mg/ha in 1985 to 17.4Mg/ha in 1995, and to 20.0Mg/ha in 2005; the 2005 value represents a 2.8Mg/ha (16.6%) increase, compared with 1985 and is attributable to the increased area of grassland and bare land. In 2020, the estimated soil loss, considering the ECVAM, was 19.2–19.3Mg/ha for the 10-year rainfall frequency, 36.4–36.6Mg/ha for the 50-year rainfall frequency, and 45.7–46.0Mg/ha for the 100-year rainfall frequency. Without considering the ECVAM, the amount of soil loss was about 0.4–1.6Mg/ha larger than estimates that did consider the ECVAM; specifically, the values were 19.6–19.9Mg/ha for the 10-year rainfall frequency, 37.1–37.8Mg/ha for the 50-year frequency, and 46.7–47.5Mg/ha for the 100-year frequency. In 2010, without considering the ECVAM, the soil loss was 0.3–1.8Mg/ha more than that estimated when considering the ECVAM. These results indicate that if urban areas are developed such that they damage areas of high value, as defined environmentally and legislatively, the amount of soil loss will increase, whereas if such areas are preserved, erosion will decrease slightly. Thus, when planning urban development, the environmental and legislative value of preservation should be considered to minimize erosion and allow for more sustainable development.