Soil erosion and sediment yield in tropical mountainous watershed of northwest Thailand: the spatial risk assessments under land use and rainfall changes

摘要

A GIS-based method has been applied for assessing the spatial soil erosion risk and sediment yield in Mae Rim watershed, Northwest Thailand. The gross soil erosion in each watershed cell was estimated using the Revised Universal Soil Loss Equation (RUSLE) by thoroughly determining its various parameters. RUSLE results showed mean annual soil loss rate of 31 tonnes ha(^{-1}) yr(^{-1}), while the mean annual suspended sediment yield was 7.4 tonnes ha(^{-1}) yr(^{-1}). From the results of the spatial analysis between controlling factors and soil erosion, it indicated that bare land, field crop land and high steep slope were linked to extreme soil erosion (> 150 tonnes ha(^{-1}) yr(^{-1})). With respect to soil erosion under land use and rainfall change, it was revealed that the conversion from deciduous forest to field crop area has very serious implications for soil erosion in the Mae Rim watershed. Indeed, transition from forest to agriculture may lead to erosion increase despite reduced rainfall. The results obtained from analysing scenario sensitivities identify synergistic effects on soil erosion hazard if bare land, field crop land and rainfall erosivity are increased simultaneously in the future.