A study on rational slopeland classification for land conservation in Taiwan: a case of Jhuoshuei River before Typhoon Morakot

Promulgated in 1976, “Slopeland Conservation and Utilization Act” aims to regulate the scope of slopelands. “Classification Standard of Slopeland Utilization Limitations” was set forth, classifying slopelands into lands suitable for agricultural, animal husbandry, or forestry purposes or as lands subject to strengthened conservation according to their average slope, soil effective depth, soil erosion degree, and parent rock. Overall inventory was carried out based on the said four factors to verify the classification standard of slopeland utilization limitations. However, the currently verified lands are mostly suitable for forestry or for agriculture and animal husbandry. Scattered placement of these lands results in critical issues such as segmented land use and impaired landscape and ecotype. Especially for lands verified as disaster-prone, they are immediately harmful to land conservation when typhoon or heavy rain occurs. Therefore, this study aims to research rational utilization of slopelands and use for land conservation in Taiwan. Jhuoshuei River is selected as the scope of the case study, using watersheds as analysis units. Seven vulnerability factors are selected, namely total curvature, average slope, average elevation, SPI, standard deviation of aspect, land use, and NDVI, in companion with a model of disaster susceptibility created based on logistic regression; this model interprets the success rate curve of disaster susceptibility and gives an area under the curve of up to 91.1 %. Subsequently, the diagram of disaster potential classification results of the Jhuoshuei River is created via cluster analysis.