Dynamic Risk Analysis For Rainstorm Disaster Chain

Risk analysis has emerged as an effective and comprehensive procedure that supplements and complements the overall economy during the past three decades.In terms of natural hazards,research on risk analysis is crucially important for decision makers to implement emergency management policy,which can reduce negative impacts on society to certain extent.With the global climate change,many cities have suffered extreme natural hazards more frequently.At the same time,human activities,such as the growth of settlements,contribute to increasing the probability of the adverse impacts of natural hazards.The development of society urgently needs more effective hazard chain risk assessment methods,or multiple hazards risk evaluation models,especially under the circumstance of climate change.Risk is defined as a measure of the severity of hazards,or a measure of the probability of adverse effects.Traditional methods of assessing risks mainly utilize Geographic Information System to get risk map,and information diffusion method to deal with incomplete data sets.However,there are few papers discussing the uncertainty of multiple hazards and considering dynamic risk under time dimension.Besides,in the existing study for dynamic risk evaluation,the collected data are limited with insufficient data dimensions.Considering the above mentioned research gaps,this research proposes a brand-new model to evaluate multiple hazards dynamic risk and applies it to study typhoons and rainstorms hazards in Shenzhen.The model proposed in this research combines the variable fuzzy set theory with information diffusion method to solve the uncertainness of multiple hazards dynamic risk evaluation when data sets are incomplete.There are three parts needing to illustrate in the proposed model.Based on the definition of probabilistic risk,the proposed model takes time dimension into consideration to introduce the concept of dynamic probabilistic risk.Since the level of multiple hazards is affected by multiple indicators,the proposed model employs variable fuzzy set to calculate the relative membership degree and applies information entropy method to obtain the weights of criteria indicators for multiple hazards evaluation.Then the multiple indicators reduction model is introduced and can be used to get the comprehensive results of multiple hazards level degree.According to the concept of dynamic probabilistic risk which is charactered by insufficient data dimensions,the proposed model applies information diffusion method to estimate conditionalprobability distribution and vulnerability curve with the comprehensive multiple hazards level,time data and multiple hazards losses.In the end,the proposed model calculates the expected value of conditional probability distribution and vulnerability curve to denote multiple hazards dynamic risk.This model deals with the multiple dimension indicators of different hazard and solves the problem of limited information in dynamic risk so as to improve the accuracy of risk evaluation results.The specific innovations made by the model are:(i)The model takes time dimension into consideration to introduce the concept of dynamic probabilistic risk.(ii)Considering that different kinds of hazards have different measurement indicators for the multiple hazards evaluation,a combination model of variable fuzzy sets and the information entropy method has been proposed.(iii)According to the concept of dynamic probabilistic risk which is charactered by insufficient data dimensions,the model applies information diffusion method to estimate conditional probability distribution and vulnerability curve.(iv)Finally,the model calculates the expected value of conditional probability distribution and vulnerability curve to denote multiple hazards dynamic probabilistic risk.To illustrate the proposed model,this research applies it to study typhoons and rainstorms hazards in Shenzhen.Shenzhen locates in the southern China,a coastal city with low latitude,where the rainstorms and typhoons hazards have severely restricted the sustainable development of local economy and society.From 1990 to 2016,an average typhoon and rainstorm hazards have caused 3.4 deaths and affected 149000 people,and the average direct economic losses exceed 136 RMB millions.To assess the dynamic risk of typhoons and rainstorms hazards in Shenzhen area,this research collects the historical data about the maximum precipitation,strong wind intensity,and landing location from meteorological annual report and the typhoon website of China.According to the Classification Standards of Rainstorm and Typhoon hazards,this research uses the above data sets to obtain the multiple hazards level degree by converting the multiple hazards matrix into a single value.Combined with the multiple hazards level results,direct economic losses and time dimension,this research applies information diffusion method to estimate the conditional probability density and vulnerability curve of rainstorm and typhoon hazards.Ultimately,in accordance to the introduced concept of dynamic probabilistic risk,this research calculates the rainstorm and typhoon hazards dynamic probabilistic risk.The main results made by this research are:(i)The multiple hazards level degree can be classified into four types,and the probability of type II and III hazard occurrence is highest in August and September over the past 8 years.This result shows that emergency management department should prepare corresponding emergency plans in advance to reduce the occurrence of secondary disasters in August and September.(ii)From the perspective of hazard losses,the direct economic losses caused by typhoons and rainstorms of the same hazard level in each month are different.The result indicates that the impacts of typhoon and rainstorm hazards on the economy are not same.Besides,for the same month,the influence of economic loss decreases gradually when the hazard level degree rises.This result indicates that the capacity of rainstorm and typhoon hazards resistance in Shenzhen is reliable,and the ability to cope with the sudden hazard is relatively strong under the existing emergence system.(iii)The risk value of typhoon and rainstorm hazards in each month is different and the highest hazard risk value occurs in August and September which brings 1.14 and 1.67 billion RMB economic losses respectively.From the above conclusions,it can be seen that these results are more in line with the actual situation and can give certain guidance of the emergency management in Shenzhen.