Floods, health and climate change: A strategic review

TitleFloods, health and climate change: A strategic review
Publication TypeTyndall Working Paper
SeriesTyndall Centre Working Papers
Tyndall Consortium Institution


Secondary TitleTyndall Centre Working Paper 63
KeywordsChange, Floods, health, strategic review
AuthorsFew, R., S. Kovats, F. Matthies, and M. Ahern
Year of Publication2004

Flooding is one of the most widespread of climatic hazards and poses multiple risks to human health, yet there has been little systematic research work on health outcomes and the means by which vulnerable populations and health systems respond to those risks. Given the prospect that flood hazards may increase as a result of climate change, it is timely now to make a strategic assessment of the existing knowledge base on health and flood risk. The objectives of this report are: * To present findings from a wide-ranging review of global literature on health impacts, adaptation processes and policies relating to flood risk. * To make a critical assessment of the existing knowledge base and identify key opportunities and challenges for intervention and research. * To assess the implications of climate change and future flood risk for health impacts, adaptation processes and policies. Following preliminary discussion of global flood risk issues (chapter 2), the main sections of the report comprise an epidemiological review of the evidence base for health outcomes of flooding (chapter 3) and a review of literature analysing mechanisms of response to health risks from floods (chapter 4). Though the scope of the report is global, the material discussed in these sections is fairly narrow in thematic focus: the intention has been to maximise the added value of the work by concentrating as closely as possible on issues connected with health and flooding. The final section (chapter 5) then discusses the key findings in the wider contexts of social differentiation, development, hazard management, climate change and adaptation. Global flood risk and response Flood events can take many forms, including slow-onset riverine floods, rapid-onset flash floods, accumulation of rainwater in poorly-drained environments, and coastal floods caused by tidal and wave extremes. Both inland and coastal flooding may be associated with windstorm events. Floods also vary greatly in magnitude and impact, according to depth, velocity of flow, spatial extent, content, speed of onset, duration and seasonality. A flood event that has severe consequences (variously defined) may be termed a flood disaster, and the human impact of flood disasters is concentrated disproportionately in developing countries. Though major limitations remain in our ability to make robust projections of future rates of climate change and its effects, increasing predictive evidence of heightened global risk of inland and coastal flooding is emerging. Over the next 100 years, flooding is likely to become more common or more intense in many areas, especially in low-lying coastal sites or in zones that currently experience high rainfall. Marginal changes in the geographical distribution of flooding are also possible. However, prediction of precise locations for increased flood risk resulting from climate change is not feasible: part of the problem is that flood risk dynamics have multiple social, technical and environmental drivers. In this report we draw on a body of analytical work that defines flood risk to humans as a product of flood hazard and vulnerability, recognizing that vulnerability is constructed largely by social processes that shape people's susceptibility to harm and capacity to resist and recover. The converse concept of coping capacity emphasizes the positive potential and actions of people and societies to combat the adverse effects of flooding. Response to flood risk that involves a change in action or policy is referred to as adaptation. Coping mechanisms in response to floods can apply at all phases of the hazard management cycle: mitigation, preparedness, emergency response and recovery. The last two decades have witnessed considerable rethinking on how society should approach the management of flood hazards, with a stronger trend now toward broader aspects of flooding preparedness and a less ready reliance on structural mitigation works and emergency relief efforts. Health impacts Floods of all magnitude have the potential to impact on human health. In order to understand better the nature of this health burden the report surveys the evidence base available on the epidemiology of floods. Chapter 3 provides the substantive results of this review, with studies grouped under the following categories: mortality; injuries; diarrhoeal disease; other faecal-oral; infection from soil-transmitted helminthes; vector-borne disease; rodent-borne disease; mental health; and other health outcomes. Overall, the epidemiological review suggests that there is presently a weak evidence-base to assess the health impacts of flooding. Relatively few rigorous epidemiological studies have been undertaken, and it is extremely difficult to assess the duration of symptoms and disease, and the attribution of cause without longitudinal data. Mortality statistics are generally only available for flood disasters and datasets may be subject to bias. In developing countries accurate information on the mortality impact of flood events is particularly limited. Nevertheless, data available shows that by far the greatest burden on mortality is in Asia, and suggests that incidence of death due to inland and coastal flooding is especially high in parts of Central and South America, the Caribbean and South Asia. The speed of onset of floodwaters is a key factor determining the number of immediate flood-related deaths; few deaths from drowning occur during slow rising floods. Generally, there is very weak data available on non-drowning (non-immediate) deaths that can be attributed to the flood event. Infectious disease is a major flood-related health concern in the South, especially in settings where infectious disease transmission is an endemic public health problem. Infectious disease outbreaks have been reported following major flood events in developing countries, and these outbreaks vary in magnitude and rates of mortality. There is some evidence from India and Bangladesh that diarrhoeal disease increases after flooding. There is also good evidence of outbreaks of leptospirosis, but relatively weak evidence that flooding leads to outbreaks of other infectious diseases (e.g. cholera, hepatitis, vector-borne disease). From the studies reviewed it is clear that there is no strong evidence of outbreaks of infectious disease in countries of the North. Mental health studies relating to flood events, by contrast, come mainly from countries of the North. There is strong evidence that flooding can have an adverse effect on common disorders such as anxiety and depressive illness, especially in the elderly. One study in the USA showed that an increase in such disorders was greatest in low-income groups. Only two studies addressed mental health impacts of flooding in developing countries. There was evidence that flooding in Bangladesh was associated with increased behavioural problems in children. The lack of research in developing countries may reflect low levels of mental health service provision as well as a shortage of research expertise on mental health epidemiology. The knowledge gap on health outcomes relates in part to a need to improve monitoring and surveillance. This includes strengthening general surveillance systems for infectious diseases, and developing and enhancing specific surveillance following flood events. Many studies in the review also suffered from methodological shortcomings. We therefore make the following recommendations for the design of epidemiological studies that investigate the health impacts of floods: control groups for comparison with non-flooded populations; use of longitudinal data, or routine data in order to gain information on pre-flood levels of disease; use of objective measures of disease outcome; and improved use of routine surveillance information Priorities for future research include: the impacts of flooding on long-term mental health in both industrialised and developing countries; the impact of flooding and heavy rainfall on diarrhoeal disease, and the main routes of transmission; indirect mortality attributable to flooding (in addition to immediate deaths from drowning); and impacts on health from the disruption of health services and other life-supporting systems. Responses to the health risks from flooding Efforts to tackle the health risks from flooding include both actions that reduce vulnerability to health impacts and measures to strengthen coping capacity in the face of health risks. Health outcomes of floods can be seen as the culmination of a series of events whereby a flood hazard leads to mortality and morbidity effects in humans exposed to the hazard. Interventions can be made at various points along this process, including structural and non-structural mechanisms of flood risk management. Since such general flood avoidance mechanisms are widely discussed elsewhere, however, this report focuses attention specifically on health-related responses: by which we mean actions geared to preventing injury and illness resulting from flooding and to promoting treatment, including the continued functioning of health services. Chapter 4 reviews and analyses seven main categories of health-related responses: action in the home and the community; health and hygiene education; warning and evacuation; disease surveillance and control; health care provision; protection of health infrastructure; and water and sanitation protection and provision. The focus of these accounts is on assessing processes and policy-related issues. Together, they raise several generic considerations for policy and intervention, broadly relating to: information and education; planning, flexibility and organization; and commitment and support. The chances of effective response to health risks are greatly enhanced by reliable information on the health needs of the population and the rehabilitation needs of health, water and sanitation systems damaged by floods. Good baseline data, for example, is a prerequisite for accurate disease surveillance during floods and needs assessment. However, the ideal of high-quality data has to be considered in context: there may be a trade-off between optimization of the accuracy of data gathering and the need to provide a timely response to health impacts. A related issue is the need for communication of information to the public in a meaningful and accessible manner. Social differentiation in perception of risks and cultural barriers to effective coping and take-up of interventions, highlight the need for health promotion and flood warning activity to be tailored to local social contexts. Advance planning is key for successful health education, warning and evacuation, emergency health care provision, infrastructure protection and other aspects of health-related response to floods. At the same time, a planned approach to health-related response needs a degree of flexibility, to ensure that actions are tailored to local circumstances and needs, and to promote institutional learning from positive experiences and external examples of good practice. Efficient response to health risks from flooding also rests on effective coordination between sectors and agencies, and on effective linkage between scales of responsibility, including the relations of trust and accountability between local public agencies and communities subject to flooding. Effective response requires considerable commitment to preparedness and risk reduction, both in time and financial support. Agencies from flood-prone areas need a long-term commitment to put strategies in place and ensure they are capable of functioning when emergencies arise. External agencies need to provide a presence beyond the immediate flood relief phase, preferably with a long-term commitment to capacity building and broad-based community involvement in intervention projects. For the South, in particular, health risk reduction from floods may require an increase and/or a shift in emphasis in external funding assistance. The global knowledge gap on health responses to flooding remains wide, and the review indicates many issues and considerations that would benefit from greater research attention. In a technical sense, there is a need to evaluate the effectiveness of existing and new health protection, health promotion and system preparedness measures used in flood-prone locations. It is important also to analyse responses to 'non-emergency' floods as well as to extreme events. In parallel, social science approaches can help strengthen our understanding of processes of response by people and institutions to the health impacts of flooding. That means analysing perceptions of health risk and coping strategies of affected populations and organisations, and the economic, social, cultural and political constraints and opportunities that shape capacity to adapt. It is also recommended that research efforts should: be undertaken jointly on health impact and response, should aim to integrate findings from different spatial scales, and should inform and be informed by more generic aspects of health risk and hazards. Vulnerability and adaptation in a changing climate The final section of the report interprets the findings in terms of vulnerability, coping and adaptation to health risks from flooding, and sets them in the context of potential changes in future flood hazards as a result of climate change. Chapter 5 discusses a series of key points and related questions, grouped under four themes: health impacts and vulnerability; coping capacity; climate change and future risk; and adaptation processes and policies. The major direct and indirect health burden caused by floods is widely acknowledged, but poorly characterised and too often omitted from formal analyses of flood impacts. A major distinction exists between the health burden of floods in the North and South, linked crucially to capacities within society to protect populations from flood hazard and health risks, and to provide health care services. However, this gross distinction hides important differences between regions and countries. Differences in vulnerability are also critical at the micro-scale, shaped both by differences in people's behaviour, material assets, wellbeing and access to health care, and by wider social, economic, cultural and political processes. Diverse coping mechanisms exist in relation to flooding and health risk at a range of scales, and yet there has been little systematic research work gauging their effectiveness. It is evident, however, that there are major limitations to the application of preparedness measures for health risk reduction, many linked with issues of information and communication, organisation, funding and the mainstreaming of flood response into strategic planning. The potential for climate change to intensify or alter flood patterns means that it is likely to become a major additional driver of future health risk from flooding. Though predictive uncertainties and timescale issues may remain an impediment to adaptive action, many such actions are also likely to provide immediate health benefits for flood-prone populations. The climate change threat heightens the need for research, both for assessment of future health burdens and for improved analysis of current and future options for health-related response. Important insights may be gained from analyses in areas currently experiencing major shifts in flooding incidence as a result of other drivers of change. Adaptation to the increased risk posed by climate change requires a further shift of emphasis toward flood preparedness, away from an emphasis on emergency health response. For the South in particular, improvement in general health practices and infrastructure can play a vital role in reducing the specific risk from flooding: if the climate change threat were to galvanise significant improvement in health systems and related services, it could therefore be seen as a 'win-win' solution. More effort is needed to identify and communicate actions and strategies at different scales that work effectively, and adapt them to meet the needs of other contexts and regions. This may become especially important for any areas newly exposed to flood risk. Ultimately, commitment to implementing best practice in flood health risk response is likely to rest on political will, innovation in response to floods, and targeted financial support.

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