The rainfall intensity-duration control of shallow landslides and debris flows : an update

The rainfall intensity-duration control of shallow landslides and debris flows : an

update

指導教授：李錫堤 教授學生：邱奕勛報告日期： 100.6.16

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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.

Outline

IntroductionRainfall and landslide informationRainfall intensity–duration dataObjective identification of rainfall thresholdsGlobal rainfall ID thresholdsConclusions

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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)

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0.3914.82 (0.167 500)I D D

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.

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Introduction (3/3)

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Rainfall and climate variables used in the literature for the definition of rainfall thresholds for the initiation of landslides

The collected information was organized in a catalogue listing 2,626 landslide events covering the 89-year period between 1917 and 2005.

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Rainfall and landslide information (1/6)

areas for which rainfall characteristics resulting in shallow landslides

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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.

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Rainfall and landslide information (3/6)

Proportion of different shallow Landslide types.

Number of reported landslides for each rainfall event.

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Rainfall and landslide information (4/6)

Information on the exactor approximate time, date, or period of failure.

Accuracy of the temporal information.

Information on lithology.

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Rainfall and landslide information (5/6)

Climate classification, based on the Köppen climate classification system.

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Rainfall and landslide information (6/6)

Frequency of rainfall events for classes of mean annual precipitation (MAP).

Frequency of rainfall events for classesof average number of rain days (RDs)

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Rainfall intensity–duration data (1/3)

48 hr

Raw ID data. Percentile estimates of rainfall ID conditions.

moving-average filtering

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Rainfall intensity–duration data (2/3)48 hr

Normalized rainfall intensity-duration conditions (MAP).

Normalized rainfall intensity-duration conditions(RDN).

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Rainfall intensity–duration data (3/3)

Climate information for the 15 climate regions considered in this work.

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 the threshold. B. Bernoulli probability approach was used to find the scale

(intercept) α and the shape (slope) β of the power law curve.

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I D

( , )~ [( ( , )] , 0 1

( , ) {(1 ) [ ( , )] }exp[ ( , ) ]

( , ) 1 / .

P I D dbern I D P

I D z I D z I D

where z I D D I

set to 0.1 and 0.5

1 / ~ (0.001,10)

~ [0.1,2]

dunif

dunif

Global rainfall ID thresholds (1/4)

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Global rainfall ID thresholds for the initiation of shallow landslides and debris flows.

MAP

RDN

Raw data

0.25 mm/hr

Global rainfall ID thresholds (2/4)

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Validation of obtained ID and normalized-ID rainfall thresholds.

MAP

RDN

Raw data

Global rainfall ID thresholds (3/4)

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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)

Comparison with existing global thresholds

Global rainfall ID thresholds (4/4)

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Climatically subdivided thresholds

24hr 80hr

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.

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Thank for your attention

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