In order to better represent the landslide risk induced by rainstorms in Hong Kong, the GEO derives the Landslide Potential Index (LPI) by estimating the potential number of landslides based on rainfall intensity, rainfall location and spatial distribution of slopes in Hong Kong.
Based on the observations on LPI of every rainstorm that prompted Landslip Warnings since 1985, landslide risk can be generally described as follows according to the LPI:
Risk Description based on Landslide Potential Index (LPI)
| Landslide Potential Index | Risk Description |
|---|---|
| > 100 | Extremely high |
| 51 - 100 | Very high |
| 10 - 50 | High |
| < 10 | Low |
According to the records from 1985 to 2018, there were three rainstorms with LPI greater than 100 that occurred in Hong Kong. Among these rainstorms, the highest LPI is 126, corresponding to the rainstorm that occurred on 7 June 2008. The rainstorm caused 2 fatalities and 347 landslides. As for the rainstorm that occurred on 23 July 1994, it triggered a serious landslide at Kwun Lung Lau causing 5 fatalities and 3 injuries. The LPI of that rainstorm was 103 and the GEO received 214 landslide reports. The above incidents indicate that the landslide risk level is extremely high when the LPI is greater than 100. Rainstorms with LPI ranging from 51 to 100 usually triggered more than 100 landslides and 50% of them resulted in fatalities, indicating the landslide risk level is very high. Rainstorms with LPI greater than 10 but less than 50 triggered about 40 landslides on average and 6% of them resulted in fatalities, indicating that the landslide risk level is high.
The GEO will post the LPI of each intense rainstorm on this webpage (see above) when the rainstorm ends (typically when the Landslip Warning is cancelled) to inform the public of its severity. Members of the public can also view the LPI of other previous intense rainstorms in the link below:
- Landslide Potential Index of every rainstorm that prompted Landslip Warning since 1985
- More information on LPI can be found in GEO Information Note 15/2022, which can be viewed/downloaded from CEDD website (https://www.cedd.gov.hk/filemanager/eng/content_454/IN_2022_15E.pdf).