New study shows global vulnerability to river flooding is declining, but fatalities and economic costs are rising
June 3rd 2015
A team of scientists has carried out new research into the economic and human costs of flooding. The research was carried out by scientists from Columbia University, VU University Amsterdam, Deltares (a research institute in the Netherlands), the insurance firm Munich Re and the Red Cross. The authors say the new study, which was published in the Proceedings of the National Academy of Sciences, is the first to show “that trends and fluctuations in vulnerability to river floods around the world can be estimated by dynamic high-resolution modelling of flood hazard and exposure.”
The authors have reproduced historical river flood occurrence using daily climate data for the period 1980 to 2010. According to these figures, reported losses from river flooding on a global scale exceeded $23 billion a year on average, whilst the cost to human life was an average of 5,900 lives lost per annum. The largest single economic loss was a major flooding event in China in 1998, which was recorded as a loss of $40 billion.
The researchers have also produced data on changes in national and global vulnerability to river flooding over the period. Vulnerability depends on two major factors: population density and flood protection measures. For instance, more people will be impacted by flooding in a densely populated area than in a sparsely populated area, whilst flood protection measures can reduce the extent and severity of flood damage. The study measures vulnerability in two ways: by the number of lives lost relative to the size of the population exposed, and by the costs incurred as a proportion of exposed GDP.
The study finds that the world has reduced its vulnerability to river flooding by 50% between 1980 and 2010, which means that a smaller percentage of the exposed population lose their lives now compared to thirty years ago, and the clean-up costs are lower as a proportion of GDP. The scientists explain the reduction by worldwide improvements to infrastructure, flood defences, health care and channels of communication. However, they also find that the reduction in vulnerability is greater in high-income countries than in low-income countries, though the gap is gradually narrowing, with resilience increasing faster in lower income countries in the twenty-year period from 1980 to 2000.
Despite this reduction, the study finds that the total of reported economic losses and fatalities associated with river floods worldwide are still higher than they were in the 1980s. The pattern of higher losses since the 1980s is apparent in both high-income and low-income countries, as well as globally. In its fifth assessment report, the Intergovernmental Panel on Climate Change (IPCC), citing a number of recent studies, has attributed the increase mainly to population growth and economic development in flood-prone areas, and has also warned of the likelihood that climate change will increase the frequency and intensity of heavy rainfall in some parts of the world, potentially increasing flood risk. The IPCC’s fifth assessment report is available for download as a PDF document.
Adaptation and Forecasts
This new research looks at how the potential increase in flood risk could be reduced by different levels of adaptation. The study presents projections of flood losses and fatalities under 100 individual scenario and model combinations, and three possible global vulnerability scenarios. The first global vulnerability scenario – a low level of adaptation – assumes that the current vulnerability in each income region remains unchanged. With that scenario, annual economic losses from river flooding globally would see an increase in the range of 433% to 2,360% by 2080, compared to 2000 levels. A medium level of adaptation assumes that all countries currently classed as vulnerable (meaning economic and human costs are higher than the global average) raise their resilience to the current global average by 2080. Under that scenario, economic losses would be 48% lower compared to a low level of adaptation. A high level of adaptation assumes that all vulnerable countries increase their resilience to match the average across high-income countries. Under that scenario, economic losses would be 96% lower compared to a low level of adaptation.
The researchers argue that adaptation will be the key to reducing vulnerability to river flooding as the frequency and intensity of flooding rises in the future. However, they also point out that adaptation must go hand in hand with mitigation. Speaking to Carbon Brief, lead researcher Dr Brenden Jongman from VU University Amsterdam said that, in the absence of any mitigation measures, the impact of climate change will continue to increase, which means that investment in resilience will also have to increase, and increase to such an extent that it becomes economically unfeasible to sustain. He also said that the researchers had not carried out a cost-benefit analysis of adaptation in the new study, adding that the costs of such measures are likely to be enormous. The burden will be greatest in poor countries who cannot afford such measures, he said.
Last year’s Natural Hazards Risk Atlas, produced by the research organisation Verisk Maplecroft, found that the UK is one of the most vulnerable countries in the world to economic damage from flooding, ranking seventh in a league table behind the USA, China, India, Bangladesh, Germany and Japan. Population density, building density, and infrastructure built on floodplains were all said to increase the risk of flood damage from heavy rainfall.
The Atlas, which is produced annually, also found that the UK is one of the most vulnerable countries to extra-tropical cyclones, a type of storm that battered the country in the winter of 2013-2014. It said that this type of storm, which features a tight circle of low pressure at its centre, is the most disruptive and costly kind of storm to affect northern Europe, and it also warned that they could become more frequent in the future. The findings were based on an assessment of 197 countries for physical and economic exposure to twelve types of natural hazards, including earthquakes, tsunamis, storm surges, wildfires and volcanoes, as well as cyclones and flooding.
Dr Richard Hewston, Maplecroft’s Principal Environment Analyst, said: “The future scale of the problem will depend heavily on the government continuing to build resilience and apply resources through flood mitigation and risk management schemes.” However, MPs have recently warned that England’s ability to sustain current levels of flood protection faces major risks, following a report by the Public Accounts Committee. The report argued that the Treasury should agree longer budgets for maintenance spending to enable the Environment Agency to develop a long-term plan. Committee member Richard Bacon, concerned about the impact on long-term value for money, said that reducing maintenance could mean new investment in defences is needed sooner than expected.
According to the report, approximately five million properties across the country, or around one in six, are at risk of flooding from coastal, river and surface water – see the Guardian for the full story.
Jongman et al. (2015) ‘Declining vulnerability to river floods and the global benefits of adaptation.’ Proceedings of the National Academy of Sciences. DOI: 10.1073/pnas.1414439112.
To read the full article, click here.
Photo: Flood damage in the Karlin district of Prague. In August 2002, floods devastated large swathes of Europe. The floods caused considerable damage to the cities of Prague and Dresden. Via Wikimedia, licensed for reuse under this Creative Commons Licence.