# Leveraging Internet News-Based Data for Rockfall Hazard Susceptibility Assessment on Highways
## 2 Materials and Methods
### Rockfall Data Collection  
Taiwan is an island celebrated for its unique environment and diverse geological landscapes. Positioned at the convergence of tectonic plates, and in the path of Pacific typhoons, Taiwan features rugged terrain with steep slopes and high mountains, making it highly vulnerable to natural hazards such as typhoons, floods, landslides, and earthquakes. In 2005, a World Bank report indicated that 73% of Taiwan's land and population are exposed to three or more hazards, such as earthquakes, landslides, or floods, and almost 99% of its land and population are exposed to two or more hazards [11]. Taiwan may be considered one of the most vulnerable areas to natural hazards on Earth [12; 13]. Many of these hazards have been extensively studied by various researchers. However, no one has systematically and comprehensively studied rockfall hazards specifically on Taiwan's highway system or analyzed the rockfall hazard vulnerability. Taiwan has an extensive highway system. The layout of the highways relevant to this study is shown in Figure 1, and the lengths of the highways are presented in Table 1. The total length is 21,839.6 km, which includes 1061.8 km of National Expressways, 5323.2 km of Provincial Highways, 3684.1 km of City and County Highways, 11,362.7 km of District and Rural Highways, and 407.8 km of Exclusive Highways [14]. Figure 1: The highway system in Taiwan, highlighting the locations of rockfall and non-rockfall events. Rockfall events are frequent in Taiwan, yet they often go unreported in mainstream TV news and newspapers, unless they are particularly significant. Consequently, identifying these occurrences frequently necessitates consulting local news reports, posing a challenge to the comprehensive collection of rockfall events essential for hazard susceptibility analysis. To address this, we used Google Alerts, a tool that sends notifications about new online content based on specified keywords, to automatically search for relevant reports from a wide range of news sources that are typically inaccessible or unnoticed. The Google Alerts were configured to search daily for rockfall events and send pertinent news to the author. Since April 2019, we have been employing this method, which has allowed us to gather data until February 2024. Note that most internet news in Taiwan is only available for a short period online. Usually, it is not possible to search and retrieve internet news that is a few months old, let alone a few years old. The highway types targeted for this study are those listed in Table 1, which does not include farm roads, urban roads, forest roads, or hiking trails. Each rockfall event reported in the news was manually verified and geolocated using Google Earth by referencing kilometer markers and road names/numbers and utilizing street view. This meticulous process enabled us to compile a primary dataset essential for our rockfall hazard analysis. The dataset not only provides a comprehensive record of rockfall incidents, but also offers valuable insights into the spatial distribution and frequency of rockfalls across Taiwan, facilitating a more accurate and detailed hazard susceptibility assessment. In total, we identified 126 rockfall events along the Provincial Highways, 19 rockfall events along the City and County Highways, and 37 rockfall events along the District and Rural Highways. There were no rockfalls along the National Expressways and the Exclusive Highways. The rockfall locations are also shown in Figure 1 as red dots. Overall, 24.7% of the Provincial Highways experienced rockfalls, 8.2% of the City and County Highways experienced rockfalls, and 0.7% of the District and Rural Highways experienced rockfalls. In terms of the number of rockfalls per kilometer, the Provincial Highways have the highest frequency, followed by the City and County Highways, and finally the District and Rural Highways. These statistics highlight the Provincial Highways as experiencing the highest frequency of rockfall incidents and the most significant impact.