A Study Of Hazards Associated With Flood And Its Synthetic Evaluation Model

Part 1 A comprehensive analysis regarding the hazards associated with flood Background: Flood accounts for up to half of all natural disasters, and affects human health, as well as the environment we live in, in multiple ways. Although many epidemiological studies have focused on one particular aspect of the dangers associated with flood, few comprehensive studies have been reported in medical literature. Objective: To carry out a sample based investigation of the two great floods experienced in 1996 and 1998 in Hunan Province, and to reveal and analyze any regular pattern or characteristics of flood. Methods: To obtain detailed information regarding the hazards associated with flood by means of cross-sectional and retrospective epidemiological investigation, analyzing data held in medical records, interviewing those involved, and laboratory testing. Results: We investigated 55 towns, 438 villages, 20,230 families, and 75,033 people of different flood areas in Hunan province. Subjects were selected by random sampling, and 96.2% of the subjects selected responsed. Results showed that the majority of casualties resulting directly from flood event occurred in the locality with collapsed embankment (the direct injury rate was 191 per 100,000 local population, the direct mortality rate was 77 per 100,000 local population). Among these casualties, the rate of injury as a result of animal attack increased significantly (P<0.01) when compared to non-flooded regions. Therewere no direct casualties in soak flooded or flash-flooded areas. The incidence rate of infectious disease (44.3 ‰ ) and the prevalence rate of non-infectious disease (68.8‰) were significantly higher in flooded areas compared with non-flooded areas (23.9‰ and 52.1‰ respectively; P<0.01). Flash-flooded areas had the highest disease incident rate (76.4‰) and disease prevalence rate (82.3‰) of all different kinds of flood areas. The incidence and prevalence rates of all types of disease increased along with the severity of flood; the diseases with the most significantly increased incidence or prevalence were conjunctivitis (RR=83.12), dermatitis (RR=10.9), and schistosomiasis (RR=2.09). Gastrointestinal illnesses were the most common non-infectious diseases encountered (RR=1.41). The total mortality rate was significantly higher in flooded areas (939 per 100,000) than in non-flooded areas (726 per 100,000; P<0.01). The increase of total mortality was significant in flash-flooded and collapsed embankments areas (P<0.01). The relative risk of death was 1.61 and 1.44 respectively compared with non-flooded ares. Thestandard rate of years of potential life lost (SYPLL) were 16.03‰ and 21.84‰, respectively. The rate of posttraumatic stress disorder (PTSD) in the population of more than 6 years old in flooded areas was 32.6%. The rate of PTSD was higher in more severely flooded areas, in more than 20 years older age groups, and in female (34.0%) than in milder flood areas, younger than 20 years old age groups, and male (31.0%) (P<0.01). The flash-flood group had the highest rate of PTSD (57.4%), followed by group of collapsed embankment (35.8%). Floods facilitated the spread of epidemic focus of schistosomiasis in Hunan; new epidemic focus appeared in 11 towns and 52 villages in 1998. The rates of schostosoma infection and acute schistosomiasis was significantly higher in flood years than that in non-flood years (RR: 1.60, 1.95, P<0.01). Although there was no significant difference between flooded and non-flooded areas in the rates of leptospirosa and hemorrhagic fever with renal syndrome (HFRS), the density of rats and rate of rates infection of leptospirosa and HFRS virus was significantly higher in flooded areas than that in non-flooded areas (P<0.01), an outbreak of leptospirosa and HFRS was therefore identified as a potential risk. The total economic loss was 13.2 billion RMB per flood year in 55 sample towns, of which 12.7% was private loss, 87.3% was community loss, 28.5% was direct economic loss, and 71.5% was indirect economic loss. The collapsed embankment flood areas sustained the highest economic loss (35,420RMB per person), followed by flash-flood areas (9,323 RMB per person); the investment in flood prevention strategies before and during the flood years was negative related to the economic loss caused by the flood. The cost-benefit ratio of investment in anti-flood strategies was calculated to be 1:250. Conclusions: Our results showed that the hazards associated with flood were serious; it involved the environment, the society, as well as the individual. The severity of hazards was closely related to the type of flood. Preparation in advance of flood was the single most important measure for minimizing the flood damage. Implementing adequate flood responses, and in particular establishing an appropriate disease prevention scheme was also important to minimize damage associated with flood. Part 2 Research of synthetic evaluation model applied to flood hazards Background: In order to minimize the economic loss and the environmental damage due to flood, and maximize help and assistance to flood victims, it is very important to make a precise and complete evaluation when flood event occurred. The impact of flood on human health and its survival environment is multiple and complicated, thereforeany evaluation regarding the flood hazards must be fully comprehensive. All previous studies have focused upon the evaluation of a specific flood hazards; no fully comprehensive evaluation has been reported in medical literature. Objective: To create a synthetic evaluation model, which can be applied to the evaluation of flood hazards, based on a detailed investigation into the floods of Hunan province in 1996 and 1998. The model aims to be used by anti-flood managers as a practical quantitative evaluation tool. Methods: The initial evaluation indicators were selected using systematic analysis and literature data analysis. All of the initial evaluation indicators were tested using single or multiple variable analysis method, and those indicators with no statistical significance were excluded from the study. A frame of evaluation indicators was drafted using variable cluster analysis and analytic hierarchy methods. The evaluation indicators and their weight were determined using the Delphi procedure; the evaluation model of the flood hazards was established by analytic hierarchy method and rank sum ratio method; the model was tested by jackknife analysis, one-way ANOVA, and correlation analysis. Results: Based on the results obtained in Part One, 128 initial evaluation indicators were selected using systematic analysis and literature data analysis methods, of which 54 indicators with no statisticalsignificance in single variable analysis or in multiple regression analysis were excluded. The remaining 74 indicators were divided into 6 categories, which consisted of the frame of synthetical evaluation indicators by variable cluster analysis and analytic hierarchy methods. Finally, 6 First Rank Indicators and 24 Second Rank Indicators and their weight were determined by Delphi process. The First Rank Indicators were: direct casualties, the increases of incidence and prevalence rate of diseases, excess mortality rate, mental injury, epidemic focus expansion and infectious vector spreading, and economic loss. Based on the 24 indicators, two synthetic evaluation models were established using analytic hierarchy method and rank sum ratio method respectively. The results showed that the model used to classify the flood severity was reliable, the cutoff value of flood severity was suitable, the model had better differentiability, and most of the synthetic evaluation indicators were independent. Conclusions: Two synthetic evaluation models established from our study, including 24 second rank evaluation indicators, were highly comprehensive and practical model for evaluating the flood severity, with very important theoretical and practical significance in directing anti-flood. The synthetic evaluation model of analytic hierarchy method can be used to evaluat the flood severity quantitatively for any flood area, and the synthetic evaluation model of rank sum ratio method can be usedto compare the flood severity in different flood areas and sort the flood areas according to the flood severity.