Estimation of Soil Erosion Using Remote Sensing and GIS, Its Valuation and Economic Implications on Agricultural Production

*Manzul Kumar Hazarika, Institute of Industrial Science, Block-C, Ce-509, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 1538505, Japan; Kiyoshi Honda, Asian Center for Research on Remote Sensing, STAR Program, Asian Institute of Technology, P.O.Box 4, Khlong Luang, Pathumthani 12120 , Thailand. *Corresponding author: [email protected] ABSTRACT Soil erosion is a serious environmental problem in Northern Thailand causing a threat to sustainable agriculture. Faulty agricultural practices, high annual rainfall and the undulating topography of Northern Thailand are the key factors contributing to a high annual rate of soil erosion. For finding the status and extent of the erosion problem in the Mae Ao watershed of Northern Thailand, the annual rate of soil erosion was estimated using remote sensing data. Since the vegetative cover is a major factor of soil erosion, therefore, a Normalized Difference Vegetation Index (NDVI) derived from Remote Sensing data (Landsat-TM) was used in this study to assess the vegetative cover in the watershed. A soil erosion model was developed to integrate NDVI and land slope for estimating the annual soil erosion rate. Results indicated that the changes in agricultural pattern from traditional crops to orchard plantation and adoption of soil conservation measures in the Mae Ao watershed decreased the annual soil erosion rate. Estimated reduction in soil erosion rate from 1.24 mm/year in 1992 to 0.91 mm yr in 1996 in the area also lowered the external cost of soil erosion by 4,210,284 Baht. The cost of soil erosion in 1992 and 1996 were estimated as 16,010,244 Baht and 11,799,960 Baht, respectively, using replacement cost technique. The net farm income in the study area was increased from 38,262,654 Baht in 1992 to 62,740,702 Baht in 1996. However, the net farm income was reduced to 22,645,290 Baht in 1992 and 50,956,127 Baht in 1996, if the external cost of soil erosion was taken into account.