The rainfall intensityduration control of shallow landslides and

The rainfall intensity-duration control of shallow landslides and debris flows : an update Guzzetti, F. , Peruccacci, S. , Rossi, M. , and Stark, C. P. , 2008. The rainfall intensity-duration control of shallow landslides and debris flows: an update. Landslides, 5(1), 3 -17. 指導教授：李錫堤 教授 學生：邱奕勛 報告日期： 100. 6. 16 1

Outline Introduction Rainfall and landslide information Rainfall intensity–duration data Objective identification of rainfall thresholds Global rainfall ID thresholds Conclusions 2

Introduction (1/3) In 1980, Nel Caine published a paper entitled “The rainfall intensity– duration control of shallow landslides and debris flows”. I：rainfall intensity in millimeter per hour (mm/h) D：rainfall duration in hours (h) 3

Introduction (2/3) Rainfall ID thresholds are used to forecast the occurrence of shallow landslides and debris flows based on continuous rainfall measurements. To account for climatic effects, the rainfall intensity is normalized by the mean annual precipitation (MAP) and the rainy-day normal (RDN , Wilson and Jayko 1997). Rainfall thresholds can be defined physically or empirically. Regional thresholds and Local thresholds. 4

Introduction (3/3) Rainfall and climate variables used in the literature for the definition of rainfall thresholds for the initiation of landslides 5

Rainfall and landslide information (1/6) The collected information was organized in a catalogue listing 2, 626 landslide events covering the 89 -year period between 1917 and 2005. areas for which rainfall characteristics resulting in shallow landslides 6

Rainfall and landslide information (2/6) Geographical precision for the location of the rainfall and landslide events. Proportion of landslide events for which antecedent rainfall information is available. 7

Rainfall and landslide information (3/6) Proportion of different shallow Landslide types. Number of reported landslides for each rainfall event. 8

Rainfall and landslide information (4/6) Accuracy of the temporal information. Information on the exact or approximate time, date , or period of failure. Information on lithology. 9

Rainfall and landslide information (5/6) Climate classification, based on the Köppen climate classification system. 10

Rainfall and landslide information (6/6) Frequency of rainfall events for classes of mean annual precipitation (MAP). Frequency of rainfall events for classes of average number of rain days (RDs) 11

Rainfall intensity–duration data (1/3) moving-average filtering Raw ID data. 48 hr Percentile estimates of rainfall ID conditions. 12

Rainfall intensity–duration data (2/3) 48 hr Normalized rainfall intensity-duration conditions (MAP). Normalized rainfall intensity-duration conditions(RDN). 13

Rainfall intensity–duration data (3/3) Climate information for the 15 climate regions considered in this work. 14

Objective identification of rainfall thresholds (1/1) In general, a rainfall threshold is drawn visually as the (apparent) lower boundary for the rainfall conditions. New method A. threshold curve of the form was selected to describe threshold. B. Bernoulli probability approach was used to find the scale (intercept) α and the shape (slope) β of the power law curve. 15

Global rainfall ID thresholds (1/4) Global rainfall ID thresholds for the initiation of shallow landslides and debris flows. MAP Raw data RDN 0. 25 mm/hr 17

Global rainfall ID thresholds (2/4) Raw data Validation of obtained ID and normalized-ID rainfall thresholds. MAP RDN 18

Global rainfall ID thresholds (3/4) Comparison with existing global thresholds 1. Caine (1980) 2. Innes (1983) 3. Clarizia et al. (1996) 4. Crosta and Frattini (2001) 5. Cannon and Gartner (2005) 6. Threshold inferred from the entire set of ID rainfall data (this work) 7. Thresholds for two different rainfall periods (D < 48 h, and D ≥ 48 h) (this work) 19

Global rainfall ID thresholds (4/4) 24 hr 80 hr Climatically subdivided thresholds 20

Conclusions (1/1) New statistical treated outliers in an unbiased way and reduced interpretation errors. Collection of a large number of ID rainfall data through a literature search. Results of the normalization indicate that MAP and RDN did not reduce significantly. A global landslide warning system could contribute to mitigate landslide risk. 21

Thank for your attention 22