Climate Change

Planetary summer: Why Europe may have reached a point of no return on prolonged droughts, heatwaves

Droughts are becoming a new reality for Europe, latest scientific projections suggest 

By Rohini Krishnamurthy
Published: Sunday 18 September 2022
A Swiss Air Force helicopter drops water for cows in Tissiniva mountain pasture due to an ongoing drought in Charmey, Switzerland on August 10  (Photograph: Reuters)
A Swiss Air Force helicopter drops water for cows in Tissiniva mountain pasture due to an ongoing drought in Charmey, Switzerland on August 10  (Photograph: Reuters) A Swiss Air Force helicopter drops water for cows in Tissiniva mountain pasture due to an ongoing drought in Charmey, Switzerland on August 10 (Photograph: Reuters)

About 4,200 years ago, droughts swept almost every continent — from Asia and Africa to Europe, North America and South America. These arid conditions are believed to have persisted for 300 years and caused the collapse of ancient civilisations of Egypt, Mesopotamia, the Indus Valley and China.

A similar climatic pattern appears to be taking shape as most continents experience a severe, prolonged drought with rippling effects on everything from food and water to energy availability.

The Horn of Africa, which is home to the poorest nations of Djibouti, Ethiopia, Somalia and Sudan, faces its worst drought in over 40 years after receiving deficit rainfall for four years in a row.

Read East Africa drought: ‘Climate change is making La Niña impact severe’

The UN says that some 16.2 million people in Ethiopia, Somalia and Kenya are without access to reliable safe water and close to 22 million are at risk of starvation.

In China, the government issued a nationwide drought alert on August 19 as the country’s heavily populated southern provinces have been experiencing severe heatwaves for months now.

Some rivers, including parts of its longest river the Yangtze, have dried up, affecting hydropower, halting shipping and forcing major companies to suspend operations.

In a last-ditch attempt to protect the standing crops, the country’s meteorological administration in August-end launched drones for cloud seeding — charging clouds with silver iodide to form ice crystals, resulting in precipitation. According to state-owned China Central Television, the drones would eventually cover 6,000 sq km in Sichuan province.

Read China faces its longest, most severe drought ever recorded

The US is no better, with 43 states experiencing moderate drought or worse in the last week of August, according to the country’s National Integrated Drought Information System.

It says 121.5 million people and 90 million hectares are affected by the drought, which has forced several states such as Arizona and Nevada to ration their water withdrawal from rivers for farming.

In South America, central Chile has been under a drought for the past 13 years — the longest in the region in the last millennium. The central-eastern Parana-La Plata river basin is suffering its worst drought since 1944.

The occurrence of drought is particularly worrisome in Europe, which is known to have round-the-year moderate rainfall. So far, more than 60 per cent of the continent and almost all the countries are affected by varying degrees of drought.

“This year’s drought is an extraordinary event and we had not expected to see this before 2050,” Daniela Jacob, meteorologist and director of the Climate Service Center Germany, said.

Researchers warn that the frequency and spread of severe drought has also been on the rise in Europe in recent years, suggesting that the current drought might become a regular feature for the continent.

Read Europe just had its hottest summer on record

Visible shift

In the past two decades, Europe has recorded six severe droughts in 2003, 2010, 2013, 2015, 2018 and now in 2022. In contrast, the continent saw only three severe droughts —in 1949, 1976 and 1990 — in the 20th century, according to a 2021 study published by Communications Earth & Environment - Nature.

The recent droughts have also been unique in terms of spread and intensity. For instance, the 2018 droughts impacted the Nordic countries of Denmark, Finland and Sweden, which are known for abundant water resources, short summers and high precipitation.

In 2015, central and eastern parts of Europe experienced their warmest and driest summers since 1950. The 2003 drought had economic losses to the tune of $13 billion, Vital Hari, assistant professor at the Indian Institute of Technology (Indian School of Mines), Dhanbad, said.

The current drought is expected to be the worst in 500 years, according to a report released on August 22, 2022 by the Joint Research Centre, the European Commission’s science and knowledge service.

This is because the entire continent is drier than normal this year, Andrea Toreti, the author of the report, said. “In 2018, north and central Europe experienced dry conditions and the south remained wetter than normal. This had counterbalanced the negative impacts of droughts,” Toreti said.

The future droughts in Europe are more likely to be similar to the current one. Projections show that southern Europe is unlikely to get 2018-like rainfall under the high-emissions scenario, where global warming by 2100 is projected to increase by 3.3-5.4°C above the pre-industrial level.

The team published their findings in the journal Earth’s Future in 2019. These trends suggest that droughts are becoming a new reality for the continent,  Andreas Fink, professor at the Karlsruhe Institute of Technology, Germany, said.

Source: European Drought Monitor, European Environment Agency; anomaly from 1971-2000 average; projection based on RCP 8.5 scenario

Double blow

The events that led to the 2022 European droughts were set in motion last year. According to the European Commission, the 2021 winter season was 2.1°C warmer and annual precipitation was 65 per cent lower than the 1991-2020 average.

As a result, the north-western Italian Alps saw a 80 per cent snow deficit last winter, compared to the 2010-2021 period, according to the European Organization for the Exploitation of Meteorological Satellites.

By February 2022, southern Portugal, southern Spain, southeastern France and north-western Italy were the most seriously affected by the drought, which is continuing till date.

In May to August 2022, Europe experienced a series of heatwaves. In the first half of June, a heatwave hit the Iberian Peninsula, spanning Portugal and Spain. In July, it extended further north and east, towards France, UK, central Europe and Scandinavia, according to the European Commission.

On July 19, the UK for the first time breached the 40°C mark, triggering fires across east London homes. Temperatures also exceeded 40°C in France, 45°C in Spain and 46°C in Portugal, according to the European Centre for Medium-Range Weather Forecasts.

Source: NASA. European Environment Agency; anomaly from 1960 to 2019 average; projection based on RCP 8.5 scenario

Heatwaves occur when high pressure systems form over a region, causing the air to sink. The downward movement compresses and warms the air in the lower atmosphere. It also traps warm air rising from the ground.

“The effect on near-surface temperature depends on how much energy is used to evaporate water from the ground and plants and how much is heating the air,” Florian Pappenberger, director of forecasts at the European Centre for Medium-Range Weather Forecasts, wrote in a statement on August 22.

If the soil is already dry or the surface is just concrete and tarmac, then most of the energy will heat the air and increase the magnitude of the heatwave.

In the last two decades, the onslaught of combined events of drought and heatwave have occurred in 2003, 2013, 2015, 2018 and again this year.

The hotspots of such compound events include parts of western Europe, Italy, the Balkan Peninsula and northern and eastern Europe, according to a 2021 analysis published in the journal Frontiers in Climate.

Droughts in spring and early summer, followed by hot July and August, could signal the arrival of compound events within the Mediterranean region or southern Europe, the analysis said. Further, the mechanisms powering the onset of both the events are most likely the same.

One reason is the increasing atmospheric temperature. Europe’s mean temperature over land has risen by 1.94°C to 2.01°C from the pre-industrial period, according to the European Environmental Agency.

“The persistence of similar large-scale circulation anomalies is critical for the onset of both events, which partly explains why these extremes often coincide,” Gustavo Naumann, scientific researcher at CIMA Research Foundation, Italy, said.

Scientists also suspect that droughts and heatwaves can trigger each other, but the evidence so far is inconclusive.

While they appear to be interlinked in the EU, Australia, Canada and the US, the events do not show interdependence in Ukraine, Russia, China and India, says a 2019 paper published in the journal Scientific Reports authored by Toreti and his colleagues.

Why compound events behave differently in different parts of the world is still a mystery and Toreti and his team are trying to get to the bottom of it.

Winds of change

While a detailed investigation is needed to pin down the factors responsible for the 2022 drought event, scientists, for now, have a few suspects. Jacob thinks that changing atmospheric patterns are to blame. Atmospheric circulation can influence precipitation.

The westerly winds bring moisture from the Atlantic to the Europe. The continent also gets dry winds from the Arctic and the tropics. “Under climate change, the wind circulation has changed. We now have more dry winds coming from Scandinavia and the North Pole. We are also seeing dry winds from Africa blowing over the Mediterranean region. This leads to a change in precipitation pattern,” Jacob said.

The air circulation, in turn, is influenced by jet streams, which are strong winds blowing from the west to east. They act as a boundary, separating the warm air blowing from the equator and the cool air from the poles. This pattern emerges due to the temperature difference.

As the Arctic warms stronger than other regions due to climate change, the temperature difference has dropped, lowering the velocity of the jet stream. Consequently, the jet streams meander, bringing, more often, dry winds to Europe from the south and north.

There is another player called Azores High, a persistent high-pressure system over the North Atlantic. The Azores High acts as a gatekeeper of precipitation over Europe, Caroline Ummenhofer, associate scientist in the Physical Oceanography Department at the Woods Hole Oceanographic Institution, US, said.

The system causes winds to flow clockwise around northern Africa, the eastern coast of the US and western Europe. Westerly winds bring winter rainfall to the Iberian Peninsula from the North Atlantic.

Source: European Drought Monitor, European Environment Agency; anomaly from 1971-2000 average; projection based on RCP 8.5 scenario

The Iberian Peninsula receives, on average, 732 mm per year of rain. But the region has been experiencing an annual drying of 5 to 10 mm per year per decade since the 1950s. Projections show that the precipitation could drop 10-20 per cent by 2100.

In 2019, Ummenhofer collaborated with paleoclimate scientists and listed all of the Azores Highs between 850 and 2006 CE.

Read ‘Europe will witness more extreme megadroughts in the years ahead’

“We found them in 1,156 different areas. After ranking them from the largest to smallest, we took the largest 10 per cent in that list as extremely large Azores High,” Diana L Thatcher with the Department of Geological and Atmospheric Sciences at Iowa State University, US and one of the lead collaborators of the study published in Nature Geoscience in 2021, said.

Their analysis shows that Azores High began expanding after 1850, strengthening into the twentieth century, in line with human-induced global warming.

When this happens, it pushes rain further north and deprives the Iberian Peninsula of winter showers. They have found that extremely large Azores Highs occurred on average during 15 winters in the 20th century compared to roughly 10 winters for all other 100-year periods over the last 1,200 years.

Ummenhofer says that more work needs to be done. So far, the team has investigated Azores High during the winter months. “The present drought and heatwave conditions experienced in many southern and central European countries also indicate that summertime conditions in those regions are unusual. This raises a question: What role might the Azores High play during summertime?” she said.

Preliminary data indicate that the North Atlantic Oscillation (NAO) could also be involved. It is the low-pressure zone between the Azores High in Portugal and Icelandic Low.

When the difference between the two points is large, we have a positive NAO, which is linked to below average rains in southern Europe. The opposite happens when the NAO is in the negative phase triggered by a smaller pressure difference between the two points.

“In the winter of 2021, the North Atlantic oscillation was in a positive phase. This may have contributed to the precipitation deficit in northern Italy. But we need to confirm this,” Toreti said.

Mariam Zachariah from Grantham Institute, Imperial College, London, suspects that climate change influenced Europe’s hot and dry conditions.

“There is definitely a climate change signal in almost 70 per cent of the drought studies that have been conducted,” she said, adding that a formal attribution study on the link between climate change and the 2022 droughts needs to be done.

Zachariah and her colleagues from South Africa, Germany, France, Switzerland, New Zealand, Denmark, US and the UK analysed how human-induced climate change altered the likelihood and intensity of the UK heatwave from July 16 to 19, 2022. Their simulations shows that human-induced climate change made extreme temperatures of 40°C at least 10 times more likely.

Scientists are trying to understand whether human-induced climate change alters atmospheric patterns.

“This is a little complicated because we have data only for the last 40 years. This is too short a period to find statistically significant results. But one thing is certain: warmer background climate makes heatwaves and droughts more likely,” Fink said.

“We have invested some resources in developing specific attribution approach for drought events, but we have not completed the development because it is not straightforward. We plan to release and finalise the approach within the first half of 2023,” Toreti said. Attribution studies investigate the likelihood of an extreme event happening in a world without climate change, which is the 1.2°C cooler climate.

While the reasons are still being studied, researchers agree that restricting global warming and embracing adaption measures can help. Hari and his colleagues performed a simulation study on Europe in 2019 and found that the frequency of two-year-long droughts is set to see a seven-fold increase through 2100 under a high emissions scenario.

Under a moderate-emission scenario, where the temperature is projected to rise by 1.1°C to 2.6°C, such events may reduce by almost half. “This shows that there is hope if we cut down emissions,” he said.

The team published their findings in Scientific Reports in 2020. “The time for ambitious, urgent action is now. It is only through the mitigative measures of reduce, remove and repair, pursued with equal vigour and urgency that we can hope to move away from the path to disaster we’re currently set on and achieve a manageable future for humanity,” David King, chair of the Climate Crisis Advisory Group, said in a press note released on August 22.

This is important as projections do not bode well for the continent. A 2017 study published in the International Journal of Climatology show that by 2070, the entire Europe, except Iceland, will see more frequent and extreme droughts under a high emissions scenario.

This was first published in the 16-30 September, 2022 edition of Down To Earth

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