By Roz Pidcock
Without efforts to build resilience, the economic losses from global flooding are expected to rise by at least 430% by 2080, and possibly as much as 2,000%, scientists warn.
The number of global fatalities could rise by as much as 200% in the same time, according to new research published in the journal Proceedings of the National Academy of Sciences.
But ambitious adaptation efforts in flood-prone countries could cut the potential economic costs by 96% and reduce global fatalities by 69%, say the scientists.
The authors say the new study is the first to project how vulnerable the world's population and economies are to future flooding, and how adaptation could reduce the potential damages.
Between 1980 and 2012, annual reported losses from flooding exceeded $23bn with an average of 5,900 lives lost each year, according to the team of scientists from two Dutch research institutes, Columbia University, the Red Cross and insurance firm Munich Re.
The following graph from the paper shows the top 10 recorded floods with the largest economic losses globally. An event in China in 1998 tops the list with $40bn in losses.
The 10 recorded global flood events with the largest total losses (blue line). In 10 out of 10 floods, the losses are greater than the average loss rate for the income group in that year (green bars). Source: Jongman et al., (2015)
But there's more to flooding than just how much it rains. The severity of flood impacts depend on how many people and assets are exposed to the flood. More people will be affected in a densely populated area than a sparsely populated one, for example.
The extent of flood damage also depends on whether a region has taken measures to increase its resilience. If flood defences are strong enough, or if residents are evacuated early, for example, the damage will be lower than in an area less well-equipped to cope.
This is known as vulnerability and it's measured in two ways: the number of lives lost relative to the size of the population exposed; and the costs incurred as a proportion of exposed GDP.
Economy rises, vulnerability falls
Between 1990 and 2010, the world reduced its vulnerability to flooding by half, according to the new research. That means a smaller percentage of the exposed population lose their lives now than 30 years ago, and the clean-up costs are lower as a proportion of GDP.
Why? As countries' economies grow, more money goes on improving infrastructure, building flood defences, improving health care and better communication, the paper explains.
Global fatalities as a percentage of the exposed population have declined since 1990 (black dashed line). Vulnerability has been decreasing faster in the last two decades in low income countries (orange) than high income countries (green). Source: Jongman et al., (2015)
The black dotted line in the graph above shows global fatalities as a percentage of exposed population declining over time. The paper shows a similar plot for economic losses.
The other coloured lines in the graph highlight the stark difference in vulnerability between high-income and low-income countries, however.
At the end of the 2000s, the global average mortality rate was around 40 fatalities per million exposed people, and the average economic loss rate was around 6% of exposed GDP. The authors find a factor of 17 difference in mortality between high income (green) and low income (orange) countries, and a factor of three difference in economic losses.
But between the 1980s and 2000s, resilience increased faster in lower income countries than high-income countries. That means the vulnerability gap is closing, the paper explains.
Rising damages, exposure and climate change
The impact of adaptation in the past two decades is that the damages from flooding are probably less than they might otherwise have been, the paper notes.
Nevertheless, total reported economic losses and fatalities associated with floods worldwide are still a lot higher than they were in the 1980s. You can see this in the graphs below.
The left one shows total deaths from flooding globally between 1990 and 2010 (red bars), compared to the 1980 to 1989 average. The right graph shows economic losses (green bars).
Economic losses are higher than the 1980s average in all but three years, lead author Dr Brenden Jongman from VU University Amsterdam tells Carbon Brief. Though a few costly flood events in the 1990s contribute most to the increasing trend since 1980, he notes.
To allow comparison, all reported economic losses are adjusted for inflation and converted to Purchasing Power Parity standards to enable comparison of values across different countries.
Change in global flood volume (blue line), annual exposed population (orange line) and exposed assets (purple line) compared to the 1980-1989 average, versus absolute fatalities (red bars) and economic losses (green bars). Source: Jongman et al., (2015)
The pattern of higher losses since the 1980s exists in both high-income and low-income countries, as well as globally. A number of studies attribute the higher flood damages in recent decades mainly to population growth and economic development in flood-prone areas.
The orange line in the graphs above shows how the exposed population has risen since 1990. Similarly, the purple line in the right-hand graph shows the increase in exposed GDP.
The new study suggests climate change may have played a role in greater losses and fatalities, too, by altering the frequency and intensity of flooding. The blue line in the graphs above show the rise in global annual flood volume since 1990.
Scientists expect climate change to increase the frequency and intensity of heavy rainfall in some parts of the world, potentially increasing flood risk. The reason is simple physics - a warmer atmosphere holds more water vapour. So, when it rains, it falls in heavier bursts.
On this point, the new paper says:
"The trend could potentially be a signal of climate change, although the time series is too short to draw strong conclusions on this aspect. Increased reporting of events in later years due to improved telecommunication could be playing a role."
Some previous research suggest climate change has, at least in part, led to an increase in past flood damage in China and Korea. But other studies in the US and Europe find no trend after accounting for changes in wealth and population.
Economic losses due to flooding are linked to income levels. Source: Jongman et al., (2015)
Scientists are much more confident about how climate change will alter flood risk in the future. As temperatures continue to rise, a number of studies predict flood damages will increase. Based on the weight of evidence, the latest report from the Intergovernmental Panel on Climate Change (IPCC) concluded:
"The fraction of global population experiencing water scarcity and the fraction affected by major river floods increase with the level of warming in the 21st century."
Not everywhere will see a rise in flooding, according to one paper. And there will still be large year-to-year variation because of natural fluctuations such as El Niño, the new paper notes.
Building on floodplains means that the exposure of people and assets to flooding will be greater when floods do strike, Jongman says:
"If we can totally prevent population growth and urban expansion in flood prone areas and relocate the people who live there now, indeed, this will reduce a lot of the risk. However, we cannot achieve this. As long as people live in flood prone areas, climate change will remain a crucial element."
Stepping up adaptation
As the frequency and intensity of flooding rises in the future, adaptation will be key to keeping vulnerability to flooding down, say the researchers.
To demonstrate this, the team looked at how financial and human losses are likely to change in the future depending on whether we opt for low, medium or high adaptation.
Under the low-adaptation option - which assumes current vulnerability in each income region remains unchanged - annual losses from river flooding around the world increase by between 433% and 2,360% by 2080, compared to 2000 levels. Global fatalities increase more slowly, but could reach between 15% and 214% over the next few decades, the study shows.
The projections combine the outcomes of five global climate models and four possible emissions pathways. This is why there's quite a bit of uncertainty in the results given. You can see the results in the graph below. The left one below shows global fatalities, the right one shows economic losses. The red lines represent the low-adaptation pathway.
If all countries currently classed as vulnerable - meaning death rates and economic costs are higher than the global average - raised their resilience to the current global average by 2080, this would reduce the number of lives lost by 25% compared to the low-adaptation path, the study suggests. Economic losses would be 48% lower under this medium-adaptation scenario, equivalent to an annual saving of $233bn. This is shown by the green lines.
Projected fatalities and losses from flooding out to 2080 using different climate models, emission scenarios and socio-economic pathways. Red lines indicate a scenario with no additional adaptation, green represent medium adaptation and blue represents a high adaptation scenario. Source: Jongman et al., (2015)
The most ambitious scenario - shown by the blue lines - assumes all vulnerable countries increase their resilience to match the average across high-income countries. In this scenario, global fatalities by 2080 are 69% lower by 2080 than in the low-adaptation scenario, while the economic losses are a full 96% lower, equivalent to $468bn.
These results don't mean adaptation will be enough to deal with climate change on its own, Jongman tells Carbon Brief:
"Adaptation can be effective in dealing with a large share of the risk increase, by investing drastically in flood protection, land-use planning, relocation, early warning, etc … [However], if we don't do mitigation, climate change will keep intensifying and investments will have to keep increasing, which will eventually not be feasible anymore ... It will remain crucial to mitigate climate change … Adaptation and mitigation will have to go hand in hand."
Jongman points out that he did not do a cost-benefit analysis of adaptation in the new study, adding that the costs of such measures will likely be "enormous". The burden will be greatest in poor countries who cannot afford such measures, Jongman adds:
"Investments in adaptation measures will have to become more cost-effective than they are now in order for countries to afford them. Recent global agreements call for a larger collaboration in adaptation between high-income countries and low-income ones, which could be one part of the funding."
One thing's clear: economic losses from floods will increase drastically unless further adaptation measures are implemented in river basins around the world, the paper concludes.
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