1. Empirical Criteria for Rainfall-Induced Landslides
Professor Steve Kramer

2. Landslide Records Can take an empirical approach to the problem:
Record observed landslides along with precipitation date – Caine (1980)
Attempted to find the threshold level of rainfall needed to trigger instability
Total amount of rainfall not a good predictor by itself
Highest instantaneous intensity not a good predictor by itself
A combination of the two is effective

3. Landslide Records Caine (1980):
73 sets of intensity-duration data that produced shallow landslides and debris flows worldwide
65 mm/hr
25 mm/hr
14 mm/hr
4 mm/hr
1.6 mm/hr
1 min
10 min
1 hr
1 day
10 days

4. Landslide Records
Many others have collected data and proposed alternative thresholds
Intensity-Duration thresholds proposed at local, regional, and global scales
Global models – independent of local morphological, lithological, and land-use conditions; of local or regional rainfall patterns, and history
Regional models – scale of few to several thousand square kilometers; exhibit similar meteorological, climatic, physiographic, and soil characteristics
Local models – scale of a few to several hundred square kilometers; consider local climatic regime, geomorphological setting

5. Landslide Records Global Model: Guzzetti et al. (2007)
Collected database of rainfall events that produced shallow slides
2,626 slide events from ; 97.5% between

6. Landslide Records Global Model: Rainfall Information:
Intensity and duration of rainfall event that resulted in shallow slides and debris flows
Cumulative amount of precipitation for the event
Measures of antecedent precipitation (where available)

7. Landslide Records Global Model: Landslide Information:
Type and depth of failure – descriptions often ambiguous
Number of slope failures – usually qualitative descriptions of time, date of landslide
Lithology – generic description of main rock type

8. Landslide Records Global Model: Climate Information: Broad Categories:
Tropical – rainforest (Af), monsoon (Am), wet-dry savanna (Aw)
Arid – semi-arid steppe (Bsk), middle latitude desert (Bwk)
Humid subtropical – east coast (Cfa), mild marine west coast (Cfb), warm (Cwa), Mediterranean warm (Csa), Mediterranean cool (Csb)
Humid Continental – mild summers (Dfb), hot summers (Dwa), subarctic (Dfc)
Tundra (ET)
Highland (H)

9. Landslide Records Global Model:
NOTE: Squares are debris flows, and circles are shallow slides

10. Landslide Records Global Model:
Durations range from 7 minutes to 5 weeks
Intensities range from 0.12 mm/hr to 713 mm/hr
General trend is apparent – consistent with Caine
No significant difference between shallow slides and debris flows
Smooth threshold curve implied

11. Landslide Records Global Model:
Statistical analysis of data shows different pattern
48 hrs

12. Landslide Records Global Model: Data suggests:
Higher intensity threshold for short events (D < 48 hours)
Lower intensity threshold for long events (D > 48 hours)
48 hours is the duration for which antecedent precipitation and soil moisture conditions become important
Beyond 48 hours, intensity stays relatively constant (I ≈ 0.2 mm/hr) regardless of duration – suggests that other things (groundwater recharge etc.) play an important role
Can develop single model or composite model

13. Landslide Records Global Model: Guzzetti et al. (2008) Single Model:
Composite Model:

14. Landslide Records Global Model: Guzzetti et al. (2008) Can also break
out different sets
of climatic conditions

15. Landslide Records Local Model:
Landslide data in Seattle dates back to 1897
Most slides occur in November-April period; January is the most common month

16. Landslide Records Local Model:
Used short-term and longer term rainfall metrics
3-day cumulative precipitation
15-day cumulative precipitation (prior to 3-day period)
Developed composite boundary
NOTE: Points represent events with 3 or more slides

17. Landslide Records Local Model:
With additional data, inclined boundaries extrapolated

18. Landslide Records
Local Model:
season

19. Landslide Records
Local Model:
season

20. Landslide Records
Local Model:
season

21. Landslide Records Local Model:
For the three periods ( , , )
89% of Seattle slides were part of events above threshold ( ≥ 3 slides)
65% of all events (including surrounding area and < 3 slide events) were above threshold
Majority of slides below threshold had human influence (fill, plugged culvert, broken water pipe, excavation, improper drainage, etc.)
Indicates lower threshold may be required for developed sites

22. Landslide Records Local Model - Forecasting:
Rainfall statistics can be monitored
Near real-time plots of 3-day and 15-day values can indication potential for sliding