The Risk Assessment of the Fog Disaster Based on Vulnerability Calculating Related to the Urban Transportation Network

In well developed urban area, the atmosphere is full filled with more aerosol than in suburban and rural area for industrial pollution and automobile emissions. It is evident that the accumulation of air pollutants contributes to the intensification of fog in urban. Fog has impacts on the living of citizens, especially in traffic affairs, in which fatal collision can cause casualties and death, further more the bad air quality in fog influences human healthy heavily. So it is very necessary to assess the risk of the fog disaster in city for emergency and disaster risk management. A new method is proposed to assess the urban fog disaster risks, calculating a risk index from fog probability, fragility and vulnerability, and the index is overlapped onto the map with GIS grid cell technology. The fog probability in urban area is determined based on the observatory data. The frequency of fog days is considered to be the probability of fog disaster, and for each grid cell a value is assigned. The Fragility Exponential (FE) is computed upon the regular gird cell, in which the density of the road net is its substitution while different road types have different weight coefficients in measuring the density, and the FE can be modified according to the important facility distribution. In the end, the density of the road net is normalized and considered to be the fragility of fog disaster. The population density is used as the index of vulnerability. Moreover, the probability, fragile, and vulnerability is composed by 5:2:1 to integrally sum up as the risk index of fog disaster in urban area. A 10 year fog observatory data of Beijing district is studied to assess the fog disaster risk by spatial grid. The result indicates that the high fragility value area is consistent to the extending of highway, ring roads and high rank roads. High risk area of fog disaster distributes in urban central area with dense population, highway, ring roads extension area and airport. It's also found that the frequency of fog in southeast area of Beijing is relative higher than any other area.