Category: flooding

Africa’s resistance grows as climate crisis worsens

Africa’s resistance grows as climate crisis worsens

By Kieran Cooke

Battered by storms and droughts during a tough 2019, Africa’s resistance to the climate crisis left no room for passivity.

Attempting to come to any general conclusions on the state of a vast, varied and complex continent may be a tricky business, but Africa’s resistance to the climate crisis shows it rejects any idea of settling for victimhood.

A new report, State of the Climate in Africa 2019, published by the World Meteorological Organization (WMO), makes that clear.

It reaches some grim conclusions. Increased temperatures, changing rainfall patterns, rising sea levels and more extreme weather are threatening human health and safety across the continent, says the report.

“Climate change is having a growing impact on the African continent, hitting the most vulnerable hardest and contributing to food insecurity, population displacement and stress on water resources”, says Petteri Taalas, the WMO secretary-general.

“In recent months we have seen devastating floods, an invasion of desert locusts and now face the looming spectre of drought because of a La Niña event”, he says. “The human and economic toll has been aggravated by the Covid-19 pandemic.”

Killer cyclone

Drought caused considerable damage in 2019, particularly across southern Africa. Much of East Africa also suffered drought but then, late in the year, there was torrential rain and serious flooding and landslides in the region.

The trend, says the report, is for continuing increases in temperature: 2019 was among the three warmest years ever recorded in Africa. The WMO predicts that rainfall is likely to decrease over northern and southern regions but increase over the Sahel.

There are also likely to be more weather-related extreme events. In March 2019 Cyclone Idai hit the coast of Mozambique and went on to devastate large areas of Malawi, Zimbabwe and surrounding countries.

Described as the most destructive cyclone ever recorded in the southern hemisphere, Idai killed hundreds of people and displaced several hundred thousand.

“Climate change is having a growing impact on the African continent, hitting the most vulnerable hardest”

Sea levels are rising well above the global average in many parts of Africa, the report says. Coastal degradation and erosion is a major challenge, particularly in West Africa. More than 50% of the coastlines in Benin, Côte d’Ivoire, Senegal and Togo are eroding – a trend likely to continue in future years.

The knock-on effects of these changes in climate are considerable. Approximately 60% of the total population of Africa is dependent on agriculture for a living.

Heat and drought, plus flood damage in some areas, are likely to reduce crop productivity. Changes in climate are also leading to pest outbreaks.

In what it describes as the worst case climate change scenario, the report says crop yields could drop by 13% by mid-century across West and Central Africa, 11% in North Africa and 8% in the eastern and southern regions of the continent. Rice and wheat crops would be particularly badly affected.

Combatting the crisis

Increased heat and continually changing rainfall patterns are also likely to lead to the spread of disease – and a fall-off in economic production in many countries.

But the report does point to some positive changes, showing Africa’s resistance to the crisis. Though the continent is responsible for only a small percentage of the world’s greenhouse gas emissions, many countries in Africa are taking measures aimed at tackling climate change.

Solar power is becoming more widespread, with several large-scale projects planned. Early warning systems monitoring the approach of such cataclysmic events as Cyclone Idai are being installed across the continent.
Farm incomes in many areas are increasing, due to the application of more efficient cultivation methods, such as micro-irrigation. But good planning, based on reliable data, is essential, the report says.

“The limited uptake and use of climate information services in development planning and practice in Africa is due in part to the paucity of reliable and timely climate information”, says Vera Songwe, the executive secretary of the United Nations Economic Commission for Africa– Climate News Network


This article was originally posted on the Climate News Network.
Cover photo by Georgina Smith/CIAT (public domain), via Climate Visuals
Rainfall Explorer: Achieve next-level insight into global rainfall and flood patterns

Rainfall Explorer: Achieve next-level insight into global rainfall and flood patterns

Today, the EO4SD Climate Resilience Cluster releases the Rainfall Explorer, a cutting-edge tool that enables users to readily obtain near real-time extreme rainfall statistics for past major flood events recorded anywhere in the world.

Global annual dollar damages from floods have increased from an average of US $4bn in 1971 to around US $40bn by 2015. Despite increasing flood-related losses, there remains low capacity to understand historic flood – rainfall patterns, trends, and impacts, across most of the world. These gaps in understanding compound uncertainties about how extreme rainfall and flood hazard could change under a future climate.

All of this increases the imperative to leverage new and existing data to derive deeper insights that may improve early-warning of near-term flood risks and inform development of robust, climate resilient strategies to deal with future flood risk. Our tool, which is already used by the World Bank and Multilateral Investment Guarantee Agency, seeks to be part of the solution.

Rainfall return level and return period data during late July 2016 over Maryland (USA) visualised using the Rainfall Explorer.

It is well understood that prolonged heavy rainfall is a key trigger of major flood events globally. However, catchment characteristics, land cover, topography, drainage, flood control, and other factors (including how these change in these over time) result that flood propensity for similar amounts of rainfall varies significantly from place-to-place. Further, a range of factors lead an area to be flood-prone at a given point in time, including the height the water table, ground saturation, and river discharge. And whilst the Rainfall Explorer presents rainfall statistics over a 5-day period, destructive flash floods may be triggered by intensive rainfall falling in a few hours.

Nevertheless, analysing accumulated rainfall in the lead-up major floods in an area can help to illuminate the relationship between rainfall and flood propensity. Using this tool, users may select past floods or areas of interest to obtain rainfall statistics, including the amount of rainfall (mm) recorded 5-days prior to a flood, the return period (years) of this rainfall, and the range of the rainfall return period for the selected area or flood.

  • In turn, these statistics can assist users to:
  • Identify patterns and trends in flood occurrence, flood severity and rainfall totals, and rainfall return levels
  • Identify rainfall thresholds likely to trigger a large flood in an area of interest
  • Identify the amount of rainfall associated with a past material flood event of interest
  • Understand the likelihood of rainfall associated with past flood events
  • Find the return period (years) for a given 5-day rainfall amount (mm)
  • Find the 5-day rainfall return level (mm) for a given return period (years)
  • Map the region affected by a past flood event, together with the 5-day rainfall amount and return period associated with the event

The Rainfall Explorer currently leverages the Dartmouth Flood Observatory archive of large flood events (1984 to 2020) and a 40-year timeseries of processed Copernicus ERA5 Reanalysis daily precipitation data, at 30km x 30km spatial resolution, available near-real time (with 5 days delay from present time). ERA5-Land Reanalysis daily precipitation data, at enhanced 9km x 9km spatial resolution, will be available in early 2021. All data are stored and computed in the cloud, meaning that users may access the Rainfall Explorer using only a web browser, wherever they are.

Access the Rainfall Explorer here.


The Rainfall Explorer is an EO4SD tool led by Telespazio Vega UK and Sistema GmbH, with the support of Acclimatise and GMV. We thank the World Bank and MIGA for valuable feedback provided during the development of this tool.


This article was originally posted on the EO4SD CR website.
How many people will migrate due to rising sea levels? Our best guesses aren’t good enough

How many people will migrate due to rising sea levels? Our best guesses aren’t good enough

By Sonja Ayeb-Karlsson, Celia McMichael, Ilan Kelman, Shouro Dasgupta

An article in 2011 shocked many by suggesting that up to 187 million people could be forced to leave their homes as a result of two metres of sea level rise by 2100. Almost a decade on, some of the latest estimates suggest that as many as 630 million people may live on land below projected annual flood levels by the end of the century.

The idea that rising seas will force millions to move, unleashing a refugee crisis like no other, has now become commonplace. It’s a narrative that the media are fond of, but that does not mean it is based on evidence.

The potential scale of sea level rise is becoming clearer, but this does not necessarily translate into population movements. Everything we have learned so far suggests that decisions to migrate are far more complex than a simple flight response.

In our new review article, we looked at 33 different studies that have estimated how sea level rise will affect migration patterns. Reliable estimates are important to help support vulnerable populations, but there is deep uncertainty around the amount of people who will be exposed to rising seas, and how they will respond.

Trapped populations

We looked carefully at the methods and data sets of these studies to try and tease out uncertainties. One issue plaguing their estimates is assumptions about the number of people who will be living in vulnerable low-lying areas in the future.

Most of the studies we reviewed did note that the connections between migration and sea level rise are incredibly complex. Every person directly affected isn’t guaranteed to move away as a result. People may be just as likely to try and protect their homes against the water, by building sea walls or elevating their houses.

It’s impossible to predict how each person will respond, and there are countless reasons why someone might choose to stay in the place they call home rather than move or seek shelter elsewhere. Those who may be forced to migrate and resettle due to climate change receive far more attention than those left behind. These so-called “trapped” populations can be just as vulnerable as those on the move, if not more so.

A wooden sailboat rests on a green bank next to a palm tree which has been overwhelmed by the rising water.
Despite flooding and erosion, many of the Bangladeshis we interviewed said they cannot or do not want to leave their home villages. Sonja Ayeb-Karlsson, Author provided

Research suggests that the decision to stay or leave will have as much to do with emotional and social pressures as financial or practical reasons. People may feel afraid or find it unbearable to leave, while others lack the necessary support. Many may feel obliged to stay due to binding social ties and reponsibilities.

How the health and wellbeing of those staying behind will be affected by rising seas is poorly investigated. More research is needed to understand the realities of staying put, for those who choose to stay and those who are unable to leave.

Where do we go from here?

Research on sea level rise and migration has often tried to obtain global estimates of those likely to be affected. These are useful for drawing attention to the potential scale of future impacts, but they lack local insights that could help make the picture clearer for different areas.

Rising sea levels are just one of the many ways climate change is remaking our world. Understanding how sea level rise interacts with other environmental changes, such as increased temperatures and changing rainfall patterns will be important, but this stretches the ability to predict exact migration numbers.

A young girl stands on a concrete bank as a red, wooden boat returns from fishing.
A young girl watches as a group of men return home from a fishing trip. Sonja Ayeb-Karlsson, Author provided

Despite all the unknowns, we do know that coastal changes wrought by climate change will be significant, and they require action now. That means devising measures to prevent or reduce inundation, figuring out how to live with the water, and planning for successful ways to migrate and resettle. Evaluating options, developing scenarios, and making decisions around this must happen now, rather than waiting for the issue to become more urgent.

It is just as important to avoid repeating myths around climate change triggering vast flows of people from the so-called “Global South” seeking refuge in the so-called “Global North”. We do know that people will not inevitably flee across borders in a warming world. Where migration does happen, movements within countries are often neglected on the likely flawed assumption that most migrants are crossing borders.

The narratives create unnecessary concern while shifting focus away from what really matters – helping vulnerable people. Not only do these myths reproduce xenophobic and outdated colonial power relations based on unfounded arguments, but they also create unnecessary fear and hostile environments for migrant populations around the world.


This article was originally posted on The Conversation.
Cover photo by Artiom Vallat on Unsplash.
Rivers flood, seas rise – and land faces erosion

Rivers flood, seas rise – and land faces erosion

By Tim Radford

Polar melting cannot be separated from farmland soil erosion and estuarine flooding. All are part of climate change.

Climate heating often ensures that calamities don’t come singly: so don’t forget what erosion can do.

In a warmer world the glaciers will melt ever faster to raise global sea levels ever higher. In a wetter world, more and more topsoil will be swept off the farmlands and downriver into the ever-rising seas.

And the pay-off of silt-laden rivers and rising sea levels could be catastrophic floods, as swollen rivers suddenly change course. Since many of the world’s greatest cities are built on river estuaries, lives and economies will be at risk.

Three new studies in two journals deliver a sharp reminder that the consequences of global heating are not straightforward: the world responds to change in unpredictable ways.

First: the melting of the ice sheets and the mountain glaciers. Researchers warn in the journal Nature Climate Change that if the loss of ice from Antarctica, Greenland and the frozen rivers continues, then climate forecasters and government agencies will have to think again: sea levels could rise to at least 17cms higher than the worst predictions so far.

“Avulsions are the earthquakes of rivers. They are sudden and sometimes catastrophic. We are trying to understand where and when the next avulsions will occur”

That means an additional 16 million people at hazard from estuarine floods and storm surges.

In the last 30 years, the flow from the Antarctic ice cap has raised sea levels by 7.2mm, and from Greenland by 10.6mm. Every year, the world’s oceans are 4mm higher than they were the year before.

“Although we anticipated the ice sheets would lose increasing amounts of ice in response to the warming of the oceans and the atmosphere, the rate at which they are melting has accelerated faster than we could have imagined,” said Tom Slater of the University of Leeds, in the UK, who led the research.

“The melting is overtaking the climate models we use to guide us, and we are in danger of being unprepared for the risks posed by sea level rise.”

Dr Slater and his colleagues are the third team to warn in the last month that observations of climate already match the worst-case scenarios dreamed up by forecasters preparing for a range of possible climate outcomes.

Erosion risk rises

The latest reading of glacial melt rates suggests that the risk of storm surges for many of the world’s greatest cities will double by the close of the century. But coastal cities – and the farmers who already work 38% of the terrestrial surface to feed almost 8bn people – have another more immediate problem.

In a warmer world, more water evaporates. In a warmer atmosphere, the capacity of the air to hold moisture also increases, so along with more intense droughts, heavier rainfall is on the way for much of the world. And the heavier the rain, or the more prolonged the drought, the higher the risk of soil erosion.

In 2015 the world’s farmers and foresters watched 43 billion tonnes of topsoil wash away from hillsides or blow away from tilled land and into the sea. By 2070, this burden of silt swept away by water or blown by wind will have risen by between 30% and 66%: probably more than 28 bn tons of additional loss.

This could only impoverish the farmland, according to a study by Swiss scientists in the Proceedings of the National Academy of Sciences. It could also impoverish people, communities and countries. The worst hit could be in the less developed nations of the tropics and subtropics.

But the flow of ever-higher silt levels into ever-rising seas also raises a new hazard: hydrologists call it river avulsion. It’s a simple and natural process. As conditions change, so rivers will naturally change their flow to spill over new floodplains and extend coastal lands.

Survival in question

But river avulsions can also be helped along by rising sea levels. Since 10% of humanity is crowded into rich, fertile delta lands, and since some of the deadliest floods in human history – two in China in 1887 and 1931 claimed six million lives – have been caused by river avulsions, the question becomes a matter of life and death.

US scientists report, also in the Proceedings of the National Academy of Sciences, that rising sea levels alone could make abrupt river avulsion more probable, especially as delta lands could be subsiding, because of groundwater and other extraction.

The dangers of avulsion are affected by the rate of sediment deposit in the river channels, and this is likely to rise with sea levels. This in turn raises the level of the river and eventually a breach of a levee or other flood defence will force the river to find a swifter, steeper path to the sea.

Cities such as New Orleans and the coastal communities of the Mississippi delta are already vulnerable. “Avulsions are the earthquakes of rivers,” said Michael Lamb, of California Institute of Technology, one of the authors.

“They are sudden and sometimes catastrophic natural events that occur with statistical regularity, shifting the direction of major rivers. We are trying to understand where and when the next avulsions will occur.” – Climate News Network


This article was originally posted on The Climate News Network.
250 million coastal dwellers will face rising floods

250 million coastal dwellers will face rising floods

By Tim Radford

Once again, researchers confirm that coastal dwellers can expect worse floods, more often and more expensively.

In the next 80 years flooding around the planet’s land masses is likely to rise by almost 50%, endangering many millions of coastal dwellers.

If humans go on burning ever greater volumes of fossil fuels, while destroying ever more natural forest, then another 77 million people could be at risk of flooding, a rise of 52%.

And these floods – increasingly frequent and extending over greater areas – will put at risk cities, homes, resorts and industries valued at more than $14 trillion (£10.7tn).

This sum alone is worth 20% of global gross domestic product, the economist’s preferred indicator of economic health and wealth, according to a new study in the journal Scientific Reports.

The researchers built their argument on historic data from 681 tide-gauge stations around the world to model the growing hazard at 10,000 coastal locations.

“Compared with now, what we see as a one-in-100-year extreme flood event will be ten times more frequent because of climate change”

They conclude that the land area exposed to extreme flood will increase by more than 250,000 sq kms – an increase of 48% – to 800,000 sq kms, a threat to 252 million people.

“A warming climate is driving sea level rise because water expands as it warms, and glaciers are melting. Climate change is also increasing the frequency of extreme seas, which will further increase the risk of flooding,” said Ebru Kirezci of the University of Melbourne, Australia, who led the study.

“What the data and our model are saying is that compared with now, what we see as a one-in-100-year extreme flood event will be ten times more frequent because of climate change.”

None of this should come as a surprise to civic authorities, governments, hydraulic engineers and oceanographers: researchers have been warning for years that coastal floods driven by global heating will end up costing colossal and seemingly ever increasing sums.

On a global scale, and on regional examination, the story remains the same, and wealthy and developed societies in Europe and the US face the same rising tide of hazard as the world’s poorest in the crowded coastal cities of Africa and Asia.

Estimate too low?

A mix of more extreme storms and storm surges, combined with ever higher sea levels, will sweep away the world’s beaches and turn millions of comfortable US citizens into climate refugees.

It is even possible that researchers have under-estimated the hazard, simply because satellite-based measurements may have misread precise land elevation: in some cases, too, coasts are sinking independently of sea level rise.

The latest study identifies a series of flood “hotspots” around the world. These include south-eastern China, Australia’s Northern Territory, Bangladesh, West Bengal and Gujarat in India, the US states of North Carolina, Virginia and Maryland, and north-west Europe including the UK, northern France and northern Germany. The new map of risks takes no account of existing flood defences, but highlights the levels of threat to come.

“This is critical research from a policy point of view, because it provides politicians with a credible estimate of the risks and costs we are facing, and a basis for taking action,” said Ian Young, an engineer at the University of Melbourne, and a co-author.

“This data should act as a wake-up call to inform policy at global and local government levels so that more flood defences can be built to safeguard coastal life and infrastructure.” – Climate News Network


This article was originally posted on the Climate News Network.
Photo of New Orleans, after Hurricane Katrina had passed over. Image: By Master Sgt Bill Huntington, USAF  (public domain), via Climate Visuals
Rising heat affects Europe’s floods and droughts

Rising heat affects Europe’s floods and droughts

By Tim Radford

Patterns of Europe’s floods and droughts are starting to change: each could be more extreme, and far likelier with rising heat.

Climate change has begun to affect the pattern of Europe’s floods. The past three decades have seen “exceptional” flooding, say Austrian scientists who have worked their way through documentary records for the last 500 years.

At the same time, heat and drought affecting the continent are on the increase. The summer of 2018 broke all records for Germany, Austria and Switzerland, and by 2019 many trees in Europe’s forests were partly or entirely dead. And by 2085 rainfall could decline by a fifth, Swiss ecologists report, to alter the make-up of the forests dramatically.

Both findings are consistent with the big picture of climate change worldwide: wet seasons will become ever wetter; dry seasons too will become more extreme, according to US researchers in a third separate study.

All attempts to establish climate records involve careful interrogation of the past. Günter Blöschl of Vienna’s University of Technology and colleagues report in Nature that they sifted evidence from mountain lake beds, floodplains and 500 years of contemporary documents to identify decades more than usually rich in floods.

The floods of 1990 to 2016 in Western and Central Europe have been among the worst in history. To make sure of such a claim, the researchers identified periods of calamitous inundation across the whole region in the late 16th century and again in the 17th; and in the 18th and early 19th centuries.

“We should be preparing for the future by improving the technology to efficiently use water for crops”

If these episodes had anything in common, bygone floods happened when air temperatures were lower: fewer of them, too, happened in the summer.

“This finding seems to contradict the observation that, in some areas such as in the northwest of Europe, the recent warmer climate is aligned with larger floods,” Professor Blöschl said. “Our study shows for the first time that the underlying mechanisms have changed.

“While in the past floods have occurred more frequently under colder conditions, the opposite is the case now. The hydrological conditions of the present are very different from those in the past.”

Now, 55% of Central European floods happen in the summer, compared with 41% in previous centuries. It’s a message for planners, city chiefs and governments across the region: flood management is going to have to adapt.

So, too, is forest and woodland management, say scientists in Switzerland and Germany, who have been measuring changes in the canopies of their forests.

Growing vulnerability

For most of Europe, the single most extreme heatwave has been that of 2003: that is, until 2018. The sustained heat and aridity made temperatures in the growing season of 2018 on average 1.2°C higher than 2003, and 3.3°C higher than the average from 1961-1990.

Woodland foliage showed signs of drought stress. Leaves wilted, aged and dropped much earlier, and by 2019 many trees were dead, or partly dead. Those that survived were more vulnerable to beetle or fungal pests. Losses included beech, long considered the most drought-resistant.

Ten out of the 12 hottest growing seasons in the last 120 years have all happened this century. Climate forecasts already predict more of the same, with precipitation falling by a fifth by 2085. Foresters will have to think again about woodland design.

“Spruce was most heavily affected. But it was a surprise for us that beech, silver fir and pine were also damaged to this extent,” said Ansgar Kahmen of the University of Basel in Switzerland.

“We still need to study which tree species are good in which combinations, including from a forestry perspective. That will take time.”

Keeping Paris promise

And worldwide, farmers, foresters and water managers can also expect more of the same. As temperatures rise worldwide, dry seasons will tend to become drier, and wet seasons wetter.

US researchers report in the journal Nature Communications that they divided the world into nine land regions, and looked at annual rain or snowfall and how this fluctuated through the seasons in each of the nine from 1971 to 2000. They then looked at future temperature predictions for the rest of the century to see what happened to water availability.

The best outcome for relatively stable water supplies would be if nations could act to limit the planet’s average global temperature rise to no more than 2°C by 2100, in line with a promise made by 195 governments in Paris in 2015.

At higher temperatures the predicted scatter of flood and drought became more extreme. Once again, the message is: start planning. “We need to take precautions to optimally use how much water we have,” said Ashok Mishra of Clemson University in South Carolina.

“As the climate changes and population increases, we should be preparing for the future by improving the technology to efficiently use water for crops.” − Climate News Network


Cover photo by Villy, via Wikimedia Commons.
This article was originally posted on the Climate News Network.
Letting rivers run wild could reduce UK flooding – new research

Letting rivers run wild could reduce UK flooding – new research

By Neil Entwistle and George Heritage

The UK government currently spends £2.6 billion on flood defences in England, and that amount is set to double by 2026. Flooding in February 2020 showed how that’s likely to be a good investment, as climate change drives warmer and wetter weather each winter. But when it comes to managing rivers to prevent flooding in towns and cities downstream, we’re often our own worst enemy.

After the second world war, Britain embarked on a mission to reconstruct its rivers. Workers cut ditches to drain moorland, making it suitable for livestock farming. Looping rivers which once wound lazily through floodplains – flooding these areas once every two years or so – were straightened into rigid channels. River beds were dredged to deepen them and banks excavated to make them steeper, an unnatural situation that takes routine management to maintain.

The idea behind all of this was to reduce flooding by increasing the speed at which water moves downstream. But this also increased the power of rivers to move sediment. Gravels and cobbles dash along these modified and heavily managed rivers, accumulating where the water slows down, as it moves through towns and cities. Here, the river bed swells as sediment piles up, increasing local flood risk.

Flooding in Carlisle, December 2015. Environment Agency geomatics group, Author provided

Over 60% of the UK’s watercourses have been transformed in this way, changing the fundamental character of many British rivers – and the natural processes that would usually govern them – over just a few generations. In a new study, we found that doing nothing is often a better course of action for reducing flooding than these heavy handed attempts to mechanically alter rivers.

Going with the flow

We studied the River Caldew in Cumbria, which has caused three major floods in nearby Carlisle since 2010. Satellite data showed that straightening, deepening and embanking was common along the river between 2005 and 2016. Very little sediment was spotted in the river and across the floodplain, suggesting that almost all of it was being funnelled downstream towards Carlisle.

During this time, the channel through the city was widened in the hope that this would cause flood water to spread out and lose energy. But this only increased the problem of sediment building up within the river, creating a shallower channel through Carlisle that’s prone to overflowing.

A stretch of the Caldew near Mosedale in 2003. The channel is fairly rigid and surrounded by managed grassland. Google Earth, Author provided

Outside of the city, in parts where maintenance has been relaxed, the river has begun to return to a more natural state. Multiple “wandering” channels can now be seen alongside wide areas of deposited gravel. This is encouraging, as it suggests that the main river and its floodplain are reconnecting, allowing the sediment it transports to fall out of the channel and collect upstream.

We found that rivers which are allowed to behave more naturally are better at locking up sediment upstream, rather than letting it accumulate in unnaturally high quantities in flood-prone towns and cities. If more rivers are allowed to behave naturally and develop this way, it could help reduce future flooding.

The Caldew at Cummersdale in 2018. Note the variety of vegetation and increased gravel. Google Earth, Author provided

This hands-off approach to managing rivers is also much cheaper than hard engineering and brings a wealth of environmental benefits with it. The wandering channel system that’s evolving on the River Caldew has the greatest variety of features and habitats across the entire watercourse.

There are gravel bars, deep pools, floodplain wetlands, ponds and river cliffs. This diversity provides greater spawning habitat for fish, and cooler refuges for their fry. The open water habitats benefit amphibians, the trees and shrubs help kingfisher hunt and sand martins can nest in the river cliffs. Beetles and spiders scurry in the shingle, earning this wilder stretch of the Caldew a designation as a site of special scientific interest.

The last 75 years have seen many UK rivers change beyond recognition. The way we manage them in future must look very different. Relaxing our iron grip and allowing natural processes to flourish on rivers once more could be our best hope for reducing flooding, while reviving lost ecosystems rich in native wildlife.


This article was originally posted on The Conversation.

Cover photo from Wikimedia Commons.

Managed retreat: Moving 1 million US homes out of flood zone could save $1 trillion dollars

Managed retreat: Moving 1 million US homes out of flood zone could save $1 trillion dollars

By Will Bugler

A US-government study has found that the country could save $1 trillion dollars by removing around a million homes from flood-prone areas. The report indicates that government schemes to buy and demolish homes at high risk of repeated flooding, moving residents to higher ground, should be expanded. The report notes that climate change will drive flood risk to real estate even higher in the coming decades and warns that without action financial losses will climb substantially.

The report says that buyout programmes are essential to minimise exposure to flood risk. However, existing schemes operated by the Federal Emergency Management Agency (FEMA) are hampered due to funding shortages and the reluctance of homeowners to move.

“Flooding is the country’s biggest risk, and we just have all of these homes in the floodplain that keep getting repetitive losses,” said Keith Porter, one of the study’s authors and a structural engineering researcher at the University of Colorado. “We never should have been building in the floodplain in the first place. It’s time to solve that problem.”

According to the report, while a nationwide buyout programme would cost around $180 billion, it could save around nine times that amount – $1.6 trillion – over a 100-year period. Savings would accrue thanks to reduced costs to public disaster programmes and avoiding property damage reducing pay-outs through federally subsidised flood insurance schemes.

The report found that moving properties out of the flood zone through a buyout scheme was by far the most cost-effective way to reduce risk, saving $6.50 for every $1 spent. Other flood related protection measures such as levees and home adaptations still represented value, but were much more costly, saving $2 for every $1 spent.

The findings are important, as federal agencies consider the best course of action to reduce climate risks, faced with mounting costs from properties that are flooded repeatedly. FEMA’s National Flood Insurance Program ensures that homeowners that would otherwise be refused flood insurance can continue to insure their properties. However, “repetitive-loss properties” (those that flood repeatedly, year after year) are becoming increasingly burdensome to the programme. The government has resisted cutting funding for the flood insurance programme, as that would increase premium pay-outs considerably, or leave homes uninsurable.

A copy of the report can be found here.


Cover photo by Sandra Seitamaa on Unsplash
US coasts face far more frequent severe floods

US coasts face far more frequent severe floods

By Tim Radford

A new study of high-water levels on US coasts in 200 regions brings ominous news for those who live in vulnerable towns and cities.

By 2050, floods expected perhaps once every 50 years will happen almost every year in nearly three fourths of all the coasts under study.

And by 2100, the kind of extreme high tides that now happen once in a lifetime could wash over the streets and gardens of 93% of these communities, almost every day.

The message, from researchers led by the US Geological Survey, is that sea levels will go on rising steadily by millimetres every year, but the number of extreme flooding events could double every five years.

Researchers outline their argument in the journal Scientific Reports. They looked at the data routinely collected from 202 tide gauges distributed around the US coasts and then extended the tidal levels forward in time in line with predictions based on global sea level rise that will inevitably accompany ever-increasing global average temperatures, driven by greenhouse gas emissions from fossil fuel use.

“The impact of this finding bears repeating: sea level rise will likely cause ‘once-in-a-lifetime’ coastal flooding events to occur nearly every day before 2100”

Other scientists have warned that the damage from coastal flooding, storm surges and marine invasion will rise to colossal levels by the century’s end, that routine high-tide floods will become increasingly common, and that up to 13 million US citizens now in coastal settlements could become climate refugees.

But researchers based in Chicago, Santa Cruz and Hawaii wanted more than that: they wanted to know what sea level rise will do, as the waters lap ever higher, from year to year.

“Sea level rise is slow, yet consequential and accelerating,” they point out. “Upper end sea level rise scenarios could displace hundreds of millions of people by the end of the 21st century. However, even small amounts of sea level rise can disproportionately increase coastal flood frequency.”

The researchers selected 202 sites, most of them in sheltered harbours or bays, for their tide data: that way their record reflected the highest tides and storm surges, but not the haphazard readings of waves.

They concentrated on what they called “extreme water-level events” of the kind that happened once every 50 years, because most US coastal engineering work is based on that kind of hazard frequency. And then they started doing the calculations.

Exponential hazard growth

For nine out of 10 locations, the difference between the kind of flood that happened every 50 years and the sort that occurred maybe once a year was about half a metre. For 73% of their chosen tide gauges, the difference between the daily highest tide and the once-every-50-years event was less than a metre. Most projections for sea level rise worldwide by the end of the century are higher than a metre.

Once the researchers had set their algorithms to work, they found that even in median sea-level rise scenarios, the hazards grew exponentially. They found that all tidal stations would by 2050 be recording what remain for the moment 50-year events, every year. When they set the timetable to 2100, 93% of their locations would be recording a once-in-50-years flood every day.

“The impact of this finding bears repeating: sea level rise will likely cause ‘once-in-a-lifetime’ coastal flooding events to occur nearly every day before 2100,” they warn.

This would have profound consequences for what they call extreme events. And even in ordinary circumstances, beaches are increasingly likely to be washed away, and cliffs eroded.

The researchers conclude: “Our society has yet to fully comprehend the imminence of the projected regime shifts in coastal hazards and the consequences thereof.”


This article was originally posted on the Climate News Network.
Cover image: October 2012: Hurricane Sandy visits Manhattan. Image: By Beth Carey, via Wikimedia Commons
Even looking at flood maps can’t convince coastal residents their homes will be underwater

Even looking at flood maps can’t convince coastal residents their homes will be underwater

By Risa Palm and Toby W. Bolsen

Advertisers understand that providing consumers with the facts will not sell products. To get people to stop and pay attention, successful advertising delivers information simply and with an emotional hook so that consumers notice and, hopefully, make a purchase.

Climate communication scientists use these same principles of messaging—visual, local, and dramatic—to provide facts that will get the public’s attention. Such messaging is intended to help people understand risk as it relates to them, and perhaps change their behavior as a result.

As social scientists studying the effectiveness of climate change communication strategies, we became curious about a particular message we found online. Some houses advertised for sale in South Florida were accompanied by banner ads with messages such as “Flooding hurts home value. Know more before you buy. Find out for free now.” The ads were sponsored by the First Street Foundation through its website FloodIQ.com. The nonprofit foundation provides detailed aerial photos of present and future flooding as a consequence of rising sea level.

My colleague and I decided to survey residents of coastal South Florida to better understand how information affected their attitudes and opinions. Did these messages developed by a nonprofit organization change the perceptions of coastal residents who live in low-lying areas about the threat of coastal flooding as a result of sea-level rise?

Defining the danger to property by zip code

Many studies of climate change communication and response have been based on national surveys or more local reviews of counties and states susceptible to a range of coastal flooding. We focused our survey on a single region and a population at greatest risk: those who live in zip codes along the South Florida coast where the probability of flooding in local neighborhoods is extremely high.

Maps can be a way to see potential flood risk. [Image: floodiq/courtesy of the author]

With permission of the First Street Foundation to reproduce their maps that represent what flooding in the future might look like, we developed a survey to understand the effectiveness of tailored messages. How would this messaging impact residents’ beliefs about climate change and sea-level rise? We also asked if residents believed their communities and homes were at risk.

We surveyed more than 1,000 residents living in 166 zip codes in South Florida between October and December of 2018. All those surveyed were at risk from either the direct or indirect effects of flooding to their homes, including a decrease in property values, as coastal property is perceived as a less desirable destination.

We sampled residents of seven metropolitan areas, including Tampa-Saint Petersburg-Clearwater, Fort Myers, Key West, Miami-Dade County, Fort Lauderdale, West Palm Beach and Palm Beach, and Vero Beach. Half the sample received a map of their own city, rendered at a scale so that their city block was visible. The maps illustrated what could happen just 15 years from now at the present rate of sea-level rise if there were a Category 3 hurricane accompanied by storm-surge flooding.

[Photo: Asael Peña/Unsplash]

Does visual information make a difference?

The study was intended to assess how residents might perceive the vulnerability of their property and their communities to severe storms. We asked residents about their political affiliation and their support for policies such as zoning laws, gasoline taxes, and other measures to address climate change.

Surprisingly, we found that those who had viewed the maps were, on average, less likely to say they believed that climate change was taking place than those who had not seen the maps.

Further, those who saw the maps were less likely than those survey respondents who had not seen the maps to believe that climate change was responsible for the increased intensity of storms. Respondents who classified themselves as Republicans had the strongest negative responses to the maps.

Those who saw the maps were no more likely to believe that climate change exists, that climate change increases the severity of storms, or that sea level is rising and related to climate change. Even more dramatically, exposure to the scientific map did not influence beliefs that their own homes were susceptible to flooding or that sea-level rise would reduce local property values.

Consistent with national surveys, party identification was the strongest predictor of general perceptions of climate change and sea-level rise. However, the majority of homeowners denied that there was a risk to their property values, regardless of political affiliation.

What does it take to change minds?

We believe that the motivation of our respondents, their underlying beliefs when forming an opinion, is important when reflecting on these survey results. Specifically, people often process information or learn in a way that protects their existing beliefs or their partisan leanings.

In the case of our respondents’ general beliefs about climate change and its connection to sea-level rise, those who belonged to the Republican Party may have dismissed the maps either because they challenged their party’s stance on the issue or because they did not view the information as credible given their prior views. In the case of our respondents’ views about the future effects of sea-level rise on property values, all of the homeowners we surveyed, regardless of their partisanship, may have been motivated by their personal financial interests to reject the notion that sea-level rise would reduce their own property values.

It is important to emphasize that targeted information about climate change may lead to unintended effects. While accurate and easily absorbed information is important, it will take a much more nuanced approach to change the way people understand information. As advertisers well know, it takes more than facts to sell any product.


This article was originally published on The Conversation.
Cover photo by Epicurrence on Unsplash