An overview of soil erosion modelling

Soil erosion is one of the most important environmental issues in natural and synthetic territories. It can lead to loss of fertility, slope instability, soil truncation; etc. which causes irreversible effects on the poorly renewable soil resource. Therefore, understanding the key parameters and factors to model soil erosion will enable the conservation of soil system goods, services and resources, and will avoid the damage outside of fields caused by transported and accumulated sediments and water. In view of this, a review was carried out on previous studies to examine the concept of soil erosion and review various soil models widely used in literature. It was found that several models are used for soil assessment and prediction and these models are classified into physical (e.g. WEPP), conceptual (SEDNET) and empirical (USLE). The Universal Soil Loss Equation (USLE) and its modifications were found to be the most commonly used soil erosion models due to its simplicity, ease of use and the ability to integrate the various ecosystem parameters successfully. Furthermore, it was found that one of the major limitations associated with the use of models is lack of data for validation especially in large areas where obtaining ground data is not feasible. Although some researchers have suggested the use of correlation between modeled erosion results with factors such as land cover and management factor and soil erodibility factor as well as results of land use change analyses as alternatives for validation purpose. Others correlate the predicted soil erosion results with that of sediment yield. Some validated their soil erosion data with results of land use change analyses, slope length and slope steepness factor, land cover and management factor and soil erodibility factor. However, there is still ambiguity in the knowledge of our understanding as to which soil erosion prediction model to use. Keywords: soil erosion, model, validation, USLE, RUSL

Prediction of spatial soil loss impacted by long-term land-use/land-cover change in a tropical watershed

The devastating effect of soil erosion is one of the major sources of land degradation that affects human lives in many ways which occur mainly due to deforestation, poor agricultural practices, overgrazing, wildfire and urbanization. Soil erosion often leads to soil truncation, loss of fertility, slope instability, etc. which causes irreversible effects on the poorly renewable soil resource. In view of this, a study was conducted in Kelantan River basin to predict soil loss as influenced by long-term land use/land-cover (LULC) changes in the area. The study was conducted with the aim of predicting and assessing soil erosion as it is influenced by long-term LULC changes. The 13,100 km2 watershed was delineated into four sub-catchments Galas, Pergau, Lebir and Nenggiri for precise result estimation and ease of execution. GIS-based Universal Soil Loss Equation (USLE) model was used to predict soil loss in this study. The model inputs used for the temporal and spatial calculation of soil erosion include rainfall erosivity factor, topographic factor, land cover and management factor as well as erodibility factor. The results showed that 67.54% of soil loss is located under low erosion potential (reversible soil loss) or 0–1 t ha−1 yr−1 soil loss in Galas, 59.17% in Pergau, 53.32% in Lebir and 56.76% in Nenggiri all under the 2013 LULC condition. Results from the correlation of soil erosion rates with LULC changes indicated that cleared land in all the four catchments and under all LULC conditions (1984–2013) appears to be the dominant with the highest erosion losses. Similarly, grassland and forest were also observed to regulate erosion rates in the area. This is because the vegetation cover provided by these LULC types protects the soil from direct impact of rain drops which invariably reduce soil loss to the barest minimum. Overall, it was concluded that the results have shown the significance of LULC in the control of erosion. Maps generated from the study may be useful to planners and land use managers to take appropriate decisions for soil conservation. Keywords: Soil erosion, USLE, Landuse/cover changes, GIS, Malaysi