Climate change: Every element of global warming worsens floods and droughts – Professor Richard P Allan

Women carrying firewood walk past a cow carcass in Loiyangalani, Kenya, amid this year’s prolonged drought (Photo: Simon Maina/AFP via Getty Images)

We have already warmed the planet by more than a degree Celsius since the beginning of the industrial revolution thanks to greenhouse gas emissions, mainly from the burning of fossil fuels. And each additional future warming will continue to increase the severity of flood and drought events, when and where they occur.

Floods and droughts are a natural part of the global water cycle. Their presence is determined by fluctuations in weather and climate. Too much water at once or a lack of fresh water over one or more seasons is enough to upset the threads of society.

A steady and reliable supply of fresh water is necessary for our domestic, agricultural and industrial needs while keeping our homes and infrastructure safe. A lack of rainfall can dry out the surface and deplete our water reservoirs, but for weeks on end the ground begins to dry out, rivers and reservoirs shrink, and eventually plants and crops wither and die.

On the other hand, intense rains can run off rather than soak into the ground, causing flash floods. Heavy, sustained rains can cause rivers and lakes to overflow.

Add to this the state of the ground before an extreme event – the type of rock, terrain and vegetation and how wet or dry the ground is – and factor in the melting of ice or snow in the mix, and the floods become a complicated picture.

Despite the complexity of what drives floods and droughts, there is solid physics that explains why climate change will make them both worse.

As the planet warms, the air is able to carry more water in its gaseous, invisible form, water vapour.

A street of houses in Schuld, near Bad Neuenahr, was destroyed by floods that killed more than 220 people in Germany and other parts of Western Europe in July last year (Photo: Bernd Lauter /AFP via Getty Images)

The atmosphere becomes more thirsty and is able to more effectively draw water from the oceans and moisture from the ground in some regions, while this water is carried by the winds in monsoons and storms, fueling greater intensity precipitation in other regions.

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This means that when a drought – or a flood – occurs in a heated world, gravity is intensified by the faster movement of water from one region to another.

The previous moderate extremes are promoted to the extremes of the Premier League while the already serious events become unprecedented – elevated into a full-fledged super league, which of course nobody wants.

The situation is even more serious if we consider the cumulative effects – several disasters that strike a region several times or several regions at the same time. As we have seen recently with Hurricane Ian or Pacific Typhoon Noru, coastal flooding from storm surges can combine with flooding from heavy and sustained rainfall.

A shift between drought and floods can also aggravate bad situations; one example was the intense rains, winds and storm surges caused by several successive tropical cyclones that hit Madagascar between January and April this year. This followed a period of drought which caused what the UN described as potentially the “world’s first climate change famine” and made populations extremely vulnerable.

Equally worrisome for the global food supply, future events could attack in multiple waves, simultaneously hitting breadbasket regions with simultaneous droughts, floods or heatwaves.

In addition to making people vulnerable, drought can prepare the environment for related problems. Parched soil can amplify heat waves, as there is no moisture to dampen the force of the sun’s relentless rays which instead focus on heating the ground and the air above.

Dry vegetation combined with hot but windy conditions can also start or worsen wildfires, the destructive capacity of which has been observed in recent years in North America, Europe and China, for example.

Of the world’s 45 land regions, 19 have already seen an increase in heavy rainfall since the 1950s, while 12 have seen an increase in agricultural drought conditions. This image should spread and intensify in the future.

The Summary for Policymakers from the IPCC, which played a key role in the COP26 climate negotiations in Glasgow, said: “Projected changes in extremes are greater in frequency and intensity with each increase added to global warming.

A recent study from the University of Reading provides an example where the future is already here, with a projected intensification of the tropical dry season already evident in satellite observations for some regions such as Brazil, southern Africa and Australia.

In parts of Brazil and southern Africa, dry season droughts have increased by about a day or two every decade; by the end of the century, they could be as many as five to ten more dayswithout the rapid, substantial and sustained reductions in greenhouse gas emissions needed to limit climate change to less than 2°C of warming.

Until we reach a net zero world where all emissions are balanced by absorption by land and ocean, the world will continue to warm, and floods and droughts will worsen to progressively deplorable levels. .

Besides mitigating climate change, adapting to the inevitable is essential. The catastrophic floods in Germany and neighboring countries highlighted the unacceptable situation where hazard warnings are not communicated even though the data is available and ready to be used to protect lives.

However, it is irresponsible to claim that we have passed the point of no return, as the world approaches one of the thresholds set in the Paris climate agreement, 1.5°C of warming compared to in pre-industrial times.

Although it is still possible to limit warming to these levels in the long term, through joint political action between countries, it remains a fact that each warming will aggravate extreme events. Likewise, each additional warming avoided and each element of resilience built into our societies will contribute to limiting the cost of climate change on our health, wealth and ecological well-being.

Richard P Allan is Professor of Climatology at the University of Reading

Teresa H. Sadler