Flash Floods Increase as Mercury Climbs

Heavy rain must fall somewhere. The danger lies in where it falls and on what kind of terrain. As cities grow, the risk of flash floods rises, writes Tim Radfordfor Climate News Network

Flash flood damage in Uttarakhand, India, in 2012. Image: By European Commission DG Echo, via Wikimedia Commons

LONDON, 9 November, 2018 – Scientists once again have confirmed that humankind’s actions have triggered ever-greater extremes of rainfall – and an ever-greater rise in disastrous flash floods.

The study comes close on the heels of a warning by UN scientists of a dramatic increase in economic losses from climate-related disasters. Between 1998 and 2017, natural disasters cost the world’s nations direct losses of $2.9 trillion, and although earthquake and tsunami accounted for most deaths, floods, storms and other climate-related catastrophes accounted for 77% of the economic damage.

Scientists and engineers from China and the US report in the journal Nature Communications that flash floods now cause more deaths as well as more property and agricultural losses than any other severe weather-related hazards. These losses have been increasing for the last 50 years and over the last decade worldwide have topped $30bn a year.

And, they find, extremes in run–off from increasing extremes of rainfall are driven by what humans have done, and continue to do, to their planet: in the race for economic growth, people have burned ever more coal, oil and gas to dump ever-increasing levels of carbon dioxide emissions into the atmosphere.

Heat Hazard Rises

They have driven up global average temperatures by around 1°C in the last century, and without drastic action this average could reach 3°C by the century’s end.

As average temperatures rise, so does the hazard of extremes of heat. With every rise of 1°C the capacity of the atmosphere to absorb moisture rises by about 7%: higher temperatures are linked to ever-harder falls of rain. And rain that falls must go somewhere.

Moisture once naturally absorbed by forests, extensive wetlands or rich natural grasslands now increasingly lands on tarmacadam, brick, cement, tile or glass, to race down city streets, threaten ever more lives and sweep away costly homes, offices and bridges.

“Those who are suffering the most from climate change are those who are contributing least to greenhouse gas emissions”

Altogether one billion people are now settled in floodplains: the lives at risk are on the increase. And, the researchers warn, the losses will go on rising.

Most researchers have been unwilling to link specific floods directly to global warming. That cautious attitude shifted in the last few years as separate teams of climate scientists made connections between global warming and disastrous flooding and destructive storms in Europe, in India and in the US.

Australia – more often linked with extended drought and wildfire hazards than floods – has identified ever greater dangers from extreme rainfall.

The Nature study was based on decades of rainfall, run-off and temperature data collected on a daily basis and forms part of a widening search for ways to adapt to a danger that, inevitably, looks set to increase, particularly in the US.

Growth in Extremes

“We were trying to find the physical mechanisms behind why precipitation and run-off extremes are increasing all over the globe,” said Jiabo Yin, a Wuhan University student working at the Earth Institute in the University of Columbia, who led the research.

“We know that precipitation and run-off extremes will increase significantly in the future, and we need to modify our infrastructures accordingly. Our study establishes a framework for investigating the runoff response.”

Altogether, according to the UN Office for Disaster Risk Reduction’s latest survey, the world experienced more than 7,000 major disasters in the last two decades: floods and storms accounted for 43% and 28.2% of them and were the most frequent kinds of disaster.

Together, such disasters claimed 1.3 million lives – almost 750,000 of these to a total of 563 earthquakes and tsunamis. An estimated 4.4 billion people were hurt, or lost their homes, or were displaced or placed in need of emergency help.

Biggest Losers

The greatest economic losers were the US, with almost $945 billion, and China with $492bn. Storms, floods and earthquakes put three European nations in the top ten, with France, Germany and Italy losing around $50bn each in those two decades.

Once again, the UN study highlights the gap between rich and poor. “Those who are suffering the most from climate change are those who are contributing least to greenhouse gas emissions,” said Deberati Guha-Sapir, head of the UN’s Centre for Research on the Epidemiology of Disasters at the Catholic University of Louvain in Belgium.

“Clearly there is great room for improvement in data collection on economic losses, but we know from our analysis … that people in low income countries are six times more likely to lose all their worldly possessions or suffer injury in a disaster than people in high income countries.” – Climate News Network