本研究以理論探討崩塌型及溪床型土石流之臨界降雨條件,並就本省土石流案例之降雨特性如降雨強度、降雨延時及累積雨量等加以分析.崩塌型土石流之臨界降雨特性以總降雨量來控制;而溪床型土石流之發生則以降雨強度為決定條件.Caine (1980)[6]提出之降雨強度與降雨延時關係式可用以估算出本省921地震前土石流發生的臨界起動線,但並不適用於921地震後於中部山區所發生的土石流案例.921地震後發生土石流之臨界累積雨量明顯降低,故臨界降雨特性應考慮地文參數變動之影響.本研究建立臨界降雨特性與地文參數之關係,並以本省相關案例加以驗證.本研究建立之臨界降雨條件可配合氣象資料做即時性之土石流預警措施之參考. Knowing the threshold rainfall conditions is essential for the warning system as well as the evacuating process in areas prone to debris flows. The initiation of rainfall-induced debris flow is examined in this study based on both theoretical analysis and field data. Hydrological parameters, such as rainfall intensity, rainfall duration and total rainfall, of 29 debris flow events are carefully evaluated. The threshold curve proposed by Caine (1980) is valid for the debris flows prior to the 921 Chi-Chi Earthquake only. Since many landslides and slope failures occurred during and after the 921 Earthquake, the amount of total rainfall triggering debris flows is considerably reduced. Consequently, the threshold conditions should reflect the change of the geological parameters. In this study, the threshold conditions for debris flows of both landslide type and mobilized type are proposed and evaluated based on field rainfall data. For landslide type debris flows, the total rainfall is the dominant factor. While the value of peak rainfall intensity determines the occurrence of mobilized type debris flows. 研究期間：9101 ~ 9112
