Towards a framework for analysing public health impacts from cascading effects of urban floods [MSc. thesis research]

Many urban cities face a challenge in regards to long lasting impacts of urban flooding. These impacts may include psychological damages, environmental destruction, health deterioration, loss of life and structural damages, which are generally ignored as they are the secondary effects or after-effects of a flood event. The secondary effects are the consequences of direct flood damages to critical urban infrastructures, such as, utility networks, road transportation and many others. In a complex urban environment, various critical infrastructures and services are dependent on one another, causing interdependency. This interdependency generates cascading effects when a flood event occur which refers to domino-effect, where a series of continuous events occur, eventually generating a much larger disruption affecting the whole community. In case of urban flooding, it may include the flooding of streets and overflowing of combined sewers which may result in floodwater being contaminated with various pathogens causing different diseases once humans are exposed to it. Therefore, exposure to urban floodwater poses a great health risk with increase in frequency of flood events. In this study, a framework to support Quantitative Microbial Risk Assessment (QMRA) is developed and then applied on a case study of Sukhumvit Area of Bangkok in Thailand in order to analyse public health impacts from cascading effects of urban floods using MIKE+ software for one flooding event. The probability of infection was assessed on two exposure groups of adults and children because of accidental ingestion of contaminated floodwater mixed with human faeces. The QMRA was based on the ratio of concentrations of three reference pathogens, E. coli 0157:H7, Norovirus and Cryptosporidium relative to indicator microorganism, non-pathogenic E. coli. The probability of infection and illness was calculated as public health risk. The risk of illness was very low for Cryptosporidium and E. coli 0157:H7, in the range of 0.0002% to 0.0007% for Cryptosporidium and 0.0003% to 0.0009% for E. coli 0157:H7. The risk of illness for Norovirus ranged from 0.60% to 1.30%. The overall risk of illness in the exposure group of children was higher than in adults. The risk of illness for adults and children ranged from (0.0002% to 0.6%) and (0.0007% to 1.30%), respectively. The number of people developing diarrheal illness from one flood event was quantified as 55. This research work shows the applicability of QMRA framework on developing countries with limited data and the result of such studies can give important information to the urban planners to predict spatial variation for risk of infection in case of flooding and take necessary precautions to reduce the damage of cascading effects of urban floods