# New Landslide Disaster Monitoring System: Case Study of Pingding Village
## 4 Discussion  
According to the obtained rainfall data, [PERSON] established the scope of events of different gradations and provided an explanation based on 15-day pre-storm rainfall and 24 h rainstorms. Severe events brought over 100 mm of rainfall in 24 h and over 350 mm of pre-storm rainfall in 15 days, while serious events generated more than 100 mm of rainfall in 24 h and 200 mm of pre-storm rainfall. This proof of a relationship between side slope failures and rainfall encouraged many studies focusing on the threshold of rainfall for causing side slope failures. For example, it was determined that the mechanism of side slope failures is successfully triggered when the rainfall in Southern California reaches 140% of its normal rainfall (an average value of the recorded data of over 100 years) [34; 35; 36], suggesting that the threshold for Los Angeles is 125% (1993), which was also confirmed by [PERSON] [37]. [PERSON] and [PERSON] studied the collapse distribution of Nelson County, central U.S., after Hurricane Camille in 1969. According to their research, the hurricane, which moved from the west to the east, caused a more serious collapse of the side slopes in the west, northwest, and southwest directions. This indicates that there might be a connection between the directions of side slopes in collapse zones and hurricane routes [38]. Hong Kong has no records of collapse generated by earthquakes; however, the Geotechnical Engineering Office compared the risk of earthquakes and rainfall in terms of their generation of artificial slope collapse [39]. The study results showed that earthquakes bring a lower risk of causing artificial slope collapse than rainstorms. [PERSON], [PERSON], and [PERSON] [40] examined the side slope failures of Hong Kong through the following three steps:  
Figure 19: Relationship between rainfall and CCD data: (**a**) Cumulative rainfall of Pingding; (**b**) CCD camera 1; (**c**) CCD camera 2; (**d**) CCD camera 3. * The data provided by [PERSON] [32] were referred to and the rainfall data collected through Hong Kong's 46 automatic rainfall recorders were recorded;
* The considered rain delay was 1 h and 24 h of rainstorms, which was matched with the 30-day pre-storm rainfall;
* The timing of side slope failures was documented based on the reports of the National Fire Agency. According to the above research, based on the relationship between disaster numbers and rain intensity, the authors [40] concluded that over half of the studied side slope failures in Hong Kong were caused by local brief rain showers, and that the threshold for triggering side slope failures is crossed when the rain intensity reaches 70 mm/h. [PERSON] [41], who discussed the influences of different factors on the mechanism of side slope slips through on-site measurement data, focused on the slopes (28 K + 900 to 31 K + 500) along the roads near Wuwanzi in Gongtian village, which is in the township of Fanlu in Jiayi county. As part of the old landslide region, this area has suffered from landslides for a long time--since the opening of the road. Several measurement devices have been installed for two-year periods since the beginning of 2000, carrying out consistent observations of local strata, land surface deformation, the underground water level, and rainfall. Relevant discussions have also been carried out in coordination with basic theory and indoor experiments. According to the observation results, the condition of this particular area is extremely unstable. It has also been discovered that the slip behaviors of this area are highly related to rainfall. The monitoring data since 2000 indicate that the cumulative rainfall needed for accelerated side slope slips is 80-270 mm, which equals a cumulative rainfall of 3-5 days.