Floods in Spain: this extreme weather will eventually return

With climate change, water poses a problem, whether through its lack or its excess. The dramatic floods that occurred in Spain on October 29 and 30, 2024, which caused nearly 100 deaths, provide a new illustration of this.

The situation in France in spring 2024 clearly illustrated the contrast: Extreme drought in the Pyrénées-Orientales, flash floods in the Gard or even floods in the Pas-de-Calais.

These two types of climatic disasters are in reality two sides of the same coin, made more frequent and/or more intense across France, and sometimes all at the same time, with alternating drought and floods. on the same territories. It is a new water cycle, sometimes disrupted, to which territories must adapt.

The opportunity for the paleoclimatologist and former vice-president of group 1 of IPCC (group responsible for evaluating the scientific aspects of the climate system and climate change) Jean Jouzel to recall some key issues linked to water in the context of climate change.

How can climate change cause both more drought and more severe weather?

This may seem counterintuitive, but recent flooding in northern France and the persistent drought in the Pyrénées-Orientales are subject to the same mechanics on a global scale. To understand what is happening, we must return to the water cycle and start from the starting point, namely precipitation.

Because climate change has contrasting effects, and this has been documented by numerous scientific studies and recently by the IPCC in its 2022 report. Globally, temperatures are increasing, but like ocean temperatures, precipitation levels are increasing. For each additional degree Celsius, we will observe 7% more evaporationwhich results in an increase in precipitation globally.

Overall, what is happening in France in recent months, between droughts and extreme rains, is in line with what we expected at the current level of warming. But climate change is doing things badly: there is both an increase in precipitation where there is already enough – or even excess – and a decrease where there was already little or too little. These are atmospheric circulation mechanisms of hot air laden with humidity which are involved.

What about France and the Mediterranean region?

Among the regions most vulnerable to drought, we find the Mediterranean rim. It is not the only one: the west of North America, the south of Australia and even the east of Asia are also there.

Considering the IPCC projections, recurring droughts in the south-west of France or in PACA are therefore likely to be repeated. At the same time, the Mediterranean episodes expose the inhabitants of PACA to extreme rain episodes. The two phenomena, drought in the background, and episodes of intense rain, can alternate.

Projections do not show a significant change in the level of annual precipitation in the northern half of France. What is interesting is that the projections in this region – notably those carried out by the Explore project — indicate low flow rates which will decrease by up to 50% in August and September on most rivers, due to an increase in evaporation linked to warming. This clearly shows that the annual level of precipitation is not a relevant indicator for thinking on a territorial scale.

What are the main impacts of drought on agriculture?

Once the rain has fallen and the natural reservoirs such as groundwater, lakes or rivers have been recharged, we need to see what we do with the water. But even if precipitation is the starting point, there should be no mistake about the quantity of water available:

• The torrential rains of recent weeks, given the season in which they occur, are used primarily by surface vegetation, before being able to recharge the water tables.
• In the global water balance, we too often avoid the issue of water evaporation, either by the soil or by the evapotranspiration of plants.

Then, yes, water is essential for agriculture, human food, that of animals, for biodiversity as well, and in particular for these ecosystems that we call wetlandswhich can also act as natural “buffer zones” to absorb excess water during extreme rainy episodes. We talk a lot about drought, but we must also consider that the temporary excess of precipitation must go somewhere, in a context which is that of a rise in sea level. It is the entire water cycle which is affected.

There are many socio-economic areas to take into account during droughts. One of them is crop yield. The yield of soft wheat thus increased regularly between 1955 and 1995, according to the work of researchers at INRA (since now INRAE).

But now it is stagnating, which specialists attribute to climate change, prompting the selection of new varieties. Excess water also has negative economic effects, and can harmagain, to the yields of cereal crops.

What about forests, between drought and the risk of forest fires?

It’s not just wetlands or human crops that suffer from lack of water, forests too. Drought also contributes to reducing the effect “carbon sink” (capacity to store CO₂ present in the atmosphere in the form of vegetation) of forests, while on the contrary we were counting on an increase in this effect through reforestation and afforestation…

There are actually three dangers that threaten forests:

• With the drought itself, the trees grow less well,
• Pests (diseases, insects, etc.) are seeing their range expand under the effect of climate change,
• The combination of droughts, heatwaves and storms (strong winds) is conducive to forest fires.

For the forestry world, the issue of adaptation is important. This can be done through the use of different tree species better adapted to the climateFor example.

Can the different socio-economic uses of water compete?

Yes, absolutely. Many rivers in France are used for irrigation purposes in the agricultural sector. Lakes and rivers are also used for leisure activities, such as fishing. And at the same time, water resources are also important in the field of energy, since they allow the cooling of certain nuclear power plants, for example, and ensure the proper functioning of hydroelectric dams.

In the past, episodes of drought may have forced reduce the power of the power stationsthe flow of the river no longer being sufficient and the water temperature too high to ensure their cooling. Droughts can thus cause us to reach certain industrial limits.

The Pyrénées-Orientales, for example, have been facing an extremely tense situation since 2022. The department is entering its third year of restricting water use, with water tables still mostly in the red, according to a platform developed with BRGM which makes it possible to monitor the state of the different aquifers in the basin. This tool should help the various stakeholders in the region to better prioritize water uses.

River transport of goods is another notable economic aspect of water. In August 2022, the drought hitting the Rhine had forced German transport companies to only load barges to a quarter of their usual capacity. If this were to affect the Seine, for example, it could have significant impacts in France.

Should agriculture have priority in the event of trade-offs over water resources?

Currently, the political world tends to put the agricultural world above others in the allocation of water resources, which may raise questions. I think that water is a common good, and that the way of managing the resource in France, for major watershedsmakes sense.

I would like more consultation to be carried out with all stakeholders. Certainly, irrigation is an important issue for agriculture, but so is the selection of crops adapted to climate change.

One thing is certain: compared to other countries, the water available to France represents economic wealth. And this will continue, even with climate change, if we give ourselves the means to adapt. This also involves the sobriety of uses, which is an issue of education and solidarity.

Jean JouzelEmeritus Director of Research at the Climate and Environmental Sciences Laboratory (CEA-CNRS-UVSQ)/Pierre Simon Laplace Institute, Atomic Energy and Alternative Energies Commission (CEA)

This article is republished from The Conversation sous licence Creative Commons. Lire l’article original.

---