Preliminary method for anticipating the occurrence of precipitation-induced landslides in Seattle, Washington

Analysis of precipitation data associated with historical landslide events in Seattle has resulted in the identification of precipitation thresholds for the initiation of landslides. Also, an air-temperature index for multiple landslide events is identified, and in conjunction with the precipitation thresholds, is used to develop a method for anticipating the occurrence of landslides during the December-March wet season.

The precipitation thresholds are based on 3-day cumulative precipitation that occurred immediately prior to landslide events and antecedent 15-day precipitation that occurred prior to the 3-day amounts. The data indicate that 15-day cumulative precipitation influences the amount of subsequent 3-day precipitation required to initiate landslides.

Results of the analysis also indicate that air-temperature data can be used to help identify times when conditions are conducive for the initiation of landslides. It is shown that a high percentage of precipitation-related landslides occurred on days when the daily maximum air temperature was between 46? and 56? F (9? and 13? C) and that nearly all of the slides occurred on days when the daily maximum air temperature was above 43? F (6? C).