| dc.description.abstract | This study chooses the sedimentary terrain and the slate terrain in Taiwan as the main research areas, and is complemented with the 1999 Chi-Chi Earthquake isoseismal line for further dividing the research area into three parts: the north, the middle, and the south parts. This study chooses appropriate small drainage basins as a study unit. Satellite images before and after rainfall event are choose to draw a rainfall-induced landslides inventory in each study unit. Rainfall factors, such as maximum hourly rainfall, maximum 3, 6, 9, 12, 24 hourly rainfall, total rainfall, average rainfall intensity, and rainfall duration, are used to analyze the relation between the probability of rainfall-induced landslides and the rainfall factors. Diagrams of landslide ratio to a rainfall factor are drawn. Multiple rainfall factors are also analyzed via multiple regression analysis.
Landslide ratio represents the ratio between areas of rainfall-induced landslides and area of the study unit. By observing the variation of R2 value in the mutiple regression, we can realize which combination of rainfall factors can best explain the landslides. Residuals represent the unexplained or remain of the data after regression. When the residuals are positive, it means there are more landslides than predicted, when the residuals are negative, it means the opposite. Through observing the amount of landslides varies in accordance with time, we can understand the general condition of the slope restoration in an area after being struck by an extreme event; while analyzing the variation of residuals in accordance with time allows us to understand the changes of the slope restoration in a more accurate and unbiased manner.
This research uses least squares method to conduct linear regression, and plot landslide ratio to rainfall factor diagrams. It reveals that each rainfall factor all shows good performance, as the landslide ratio increases with the rainfall and shows high value of R2. The total rainfall is shown to be the best rainfall factor, showing average R2 value reach 0.87 in each study unit. We defined the intercept of the regression line at the horizontal axis as rainfall threshold for landsliding. Although the landslide ratio curve and rainfall threshold are different in each study unit, but they are similar between neighboring units. The analyses of residuals in central Taiwan show that the landslide ratio of a similar rainfall event is higher than expected. But, the decline of residuals year by year may imply that the region is in the process of restoration. | en_US |