Taiwan Island poses very rough and steep terrain along the Central Range to east coast with only about 30% of plain area along the west coast. It suffers from strikes from typhoon and flush storms almost every year. For example, the Mindulle typhoon in July 2004 carried heavy rainfalls and raged viciously to the several counties in Middle Taiwan. The aim of this paper was to understand and document the caused landslides by means of a model using satellite images in order to assess the potential risk, to build up the attribution properties, and to compare with the past analysis result. It is hoped that we may improve our understanding about the status and trend of the catchments, drainage network, and watersheds.From the analysis results, it was found that the model to extract landslide is workable, and when the accumulation rainfall is over 1600mm, the new developed landslide was obviously added. The tatal landslide is 23,748.37 hectares, only 11 %( 2607.23 hectares) belong to mountainside range, the others were part of forest area. In terms of the scale by numbers of landslide, mostly were fallen between 0.1 to 0.5 hectares, or about 33.4% in total; if terms of area, areas between 2 to 10 hectares had 33% of the total; gradient at most number is 53% between 30 with 45 degree. It was also found that most landslides were in between 45 to 60 degrees and 25% of them were between 1,500 to 2,000 meters in altitude. It was worth mentioning that Nantou County, the 921 great earthquake site, wrap up a total of 13,270 hectares, increasing 1,792 hectares from previous report.

Taiwan Island is of mountainous with high density of population concentrated on a narrow belt of western plain. Human activities are pushing to move toward hillside and even mountains after an overdeveloping of flat plain. These include local community, agricultural zone, golf course, and road network, among others. The competition of land use with nature leads to landscape change to dramatic degree. The complex geological setting of is prone to landslide and soil erosion triggered by torrent storms if soil and water conversation are not well cared. The 921 Great Earthquake further made the soil even more vulnerable to slide and collapse. This has been seen from floods in 2004 which caused large scale damages in middle Taiwan. Hence, monitoring of hillside change becomes critical for effective and efficient land management. These changes are of spatial and temporal variability. In this paper, we analyze the statistical properties of land cover changes detecting by SPOT images from two years of continuous observations and monitoring, with ancillary data from base maps, land use maps, GIS data, and DTM. All the data handling and analysis are through a GIS system. To assess the detection accuracy, a total of well distributed 206 samples from the whole island are selected for verification. Those changed areas are then analyzed in terms of occurrence frequency associated with location and time. Spatially, the occurrence frequency is high for slope between 15%-30% with altitude of around 1500m. The occurrence frequency was also dependent on the geological risk sites and strongly related to landslide-prone sites. Preliminary, it was found that the correlation between space and time is weak. Longer observation in time may be necessary and is undergoing.