Land-cover changes and potential impacts on soil erosion in the Nan watershed, Thailand

The expansion of built environments and agriculture land in the Nan watershed, Thailand, to support the rapid increase of the national population has resulted in deforestation, thus affecting the ecological balance. This deforestation, especially in high mountainous areas, has led to serious environmental degradation. Recent reports reveal an increasing soil-erosion problem in the watershed. This study analyses land-use and land-cover (LULC) changes and their potential impact on soil erosion during a study period between 1995 and 2005. The 1995, 2000 and 2005 Landsat 5 Thematic Mapper (TM) images were acquired and classified using hybrid classification methods. Cross-tabulation methods and the Markov Chain model were then used to analyse current and future LC changes. A soil risk-assessment model was formulated to identify potential risk areas of soil erosion. The LULC data show that the watershed was predominately covered by 40% closed-canopy forests, 25% paddy fields and 10% croplands. There was a major conversion of forests to agricultural lands and urban areas. The predictive model shows that forests are most likely to convert into paddy fields and croplands. The northern and eastern regions of the watershed have a high potential risk of soil erosion. These findings can be a basis for the design and implementation of sustainable resource management plans and geographically targeted conservation measures.