# Risk Assessment of Landfalling Tropical Cyclones in China Based on Hazard Risk Theory
## 2 Materials and Methods
### Methodology
#### 2.3.5 Processing of Evaluation Indicators and Calculation of Weights  
1. The Hazard of Hazard-Causing Factors  
Generally speaking, tropical cyclones encompass three natural hazards: high winds, heavy rain, and storm surges. This study selected average daily wind speed, average daily maximum wind speed, and average daily rainfall as indicators to assess the risk posed by hazard-causing factors. Utilizing the National Meteorological Science Data Center's hourly observational data, we filtered out 1482 meteorological stations impacted by landfalling tropical cyclones over a period of 24 years (i.e., from 1997 to 2021), comprising 288 months. These stations were analyzed for average daily wind speeds, maximum wind speeds, and rainfall. Indicator weights were determined using the AHP and, as the IDW interpolation method is simple and convenient to operate, it was used to interpolate wind speed data. The amount of rainfall is closely related to terrain and, so, the longitude and latitude of data stations were used as the principal variable of the average daily rainfall index, and the terrain was used as the covariable to perform ANUSPLIN interpolation. The risk associated with these hazard-causing factors was quantified using a weighted calculation, as presented in Equation (7).  
\[H=\sum_{1}^{n}w_{i}H_{i} \tag{7}\]  
where \(H\) denotes the level of risk posed by hazard-causing factors, \(w_{i}\) is the weight assigned to each corresponding secondary indicator, and \(H_{i}\) measures the influence of each indicator. The greater the value of \(H\), the higher the risk, increasing the susceptibility of the area to tropical cyclone hazards.  
2. Sensitivity of Natural Carriers  
During the development of tropical cyclones, the terrain changes and ground roughness in the path area will affect the change in its dynamic path and gradually weaken its intensity. In this study, topographic elevation and vegetation coverage were chosen as indicators to evaluate the sensitivity of natural carriers. The vegetation coverage \(f_{c}\) was computed from NDVI distribution data according to Equation (8) [32]. Following this, the AHP was utilized to determine the weights of these indicators, and the sensitivity of the natural carriers was quantified through the weighted calculation specified in Equation (9).  
\[f_{c}=\frac{NDVI-NDVI_{soil}}{NDVI_{VEG}-NDVI_{soil}}\times 100\% \tag{8}\]  
where \(NDVI_{soil}\) denotes the NDVI value corresponding to purely bare soil pixels, replaced by the NDVI value that appears at a cumulative frequency of 0.5%; meanwhile, \(NDVI_{VEG}\) denotes the NDVI value for purely vegetated pixels, replaced by the NDVI value observed at a cumulative frequency of 99.5%.  
\[\text{N}=\sum_{1}^{n}w_{f}N_{f} \tag{9}\]  
where \(N\) represents the sensitivity of natural carriers, \(w_{f}\) denotes the weights assigned to the respective secondary indicators, and \(N_{f}\) measures the impact level of each indicator. An increased \(N\) value indicates higher sensitivity, resulting in a reduced impact of tropical cyclone hazards within the area.  
3. Integrated Risk of Tropical Cyclone Hazards  
This study integrates various evaluation indicators for both the hazard level of hazardous factors and the sensitivity of natural carriers. The calculation results for these indicators are presented in Table 2. The formula for calculating the comprehensive risk of tropical cyclone hazards is (10):  
\[CRTY=\sum_{k=0}^{n}\text{C}_{k}W_{k} \tag{10}\]  
where \(CRTY\) represents the comprehensive risk of tropical cyclone hazards. A higher \(CRTY\) value indicates a greater overall risk, whereas a lower value indicates a lesser risk. \(\text{C}_{k}\) denotes the impact level of each indicator at the indicator layer, and \(W_{k}\) signifies the weight of each indicator in the overall ranking.