Serge Zaka: "Too Much Water or Not Enough: Climate Change Isn't Just an Endless Drought."

"Cloud Hunter": this is how climatologist and agroclimatologist Serge Zaka willingly defines himself. A specialist in meteorological risks for crops, he has been analyzing the interactions between climate and agriculture and their concrete consequences for farmers for several years.

His analyses are regularly disseminated on his site Agroclimat2050, launched in 2022, dedicated to agroclimatology and the adaptation of agriculture to climate change. Day after day, meteorological analyses, agroclimatic maps, and breakdowns of extreme climate events shed light on climate news.

During a round table organized at the La Ferme Digitale stand at the 2026 International Agricultural Show, he returned to a central point: the transformation of the water cycle in France and its consequences for agricultural systems.

A Disrupted Water Cycle

"In agriculture, there is a saying: bad weather is the one that lasts. The problem of climate change, at least regarding water, is clear: drought periods will lengthen and rain episodes will become more intense, sometimes more prolonged."

For farmers, this means having to deal with much more contrasting water situations. "On the ground, climate change translates into an intensification of the water cycle: more droughts, but also more violent rains."

Warning: "Climate change is not an eternal drought"

Serge Zaka emphasizes a point he believes is often misunderstood in public debate. "I really want you to leave here saying that climate change is not necessarily an eternal drought," he tells the audience. "This is often the image that dominates in the media during the summer." According to him, the reality observed on the ground is more complex: "climate change intensifies the water cycle in both directions."

This evolution does not manifest uniformly across the territory. "It is even more pronounced in the north with excesses and in the south with deficits," specifies Serge Zaka.

Milder Winters, Therefore More Rainy

The evolution of the water cycle is based on a well-known physical mechanism. "Every degree gained in the atmosphere means 7% more water vapor. This is the Clausius-Clapeyron law," recalls Serge Zaka. "And so the hotter it gets, the more water the air can hold, and thus the more precipitation it can bring."

In this context, milder winters favor more abundant precipitation. The warming of the seas and oceans around France also increases the amount of energy and humidity available in the atmosphere.

More Intense Rain Episodes

This more humid atmosphere also favors more intense precipitation episodes. Serge Zaka cites several recent episodes that illustrate this increased variability: the significant drought of 2022, but also the water excesses observed in 2024 or at the beginning of 2026. For him, these alternations of extremes precisely reflect this intensification of the water cycle: "water excesses that fall all at once: 50 mm of rain regularly, sometimes even 100 mm, as during Cyclone Kirk in 2024, on October 11, if I’m not mistaken," recalls the climatologist.

These events can lead to more frequent flooding in certain areas of the territory, particularly on the Atlantic coast, in Vendée.

Longer Summer Droughts

Conversely, summer periods may experience prolonged water deficits. "Subtropical anticyclones tend to move up from the Mediterranean to France, leading to longer drought periods."

The rise in temperatures also increases evaporation and plant transpiration, which contributes to reducing soil moisture.

Different Impacts Depending on Crops

The impact of these climatic changes varies according to crops and their agronomic calendar. They complicate the agronomic management of plots. Water excesses can thus favor certain diseases in winter crops, while summer water deficits can hinder the growth of summer crops.

Winter crops, such as wheat, barley, or rapeseed, mainly develop during the cold season. They may be more confronted with water excesses and associated diseases.

Conversely, summer crops – corn, soybeans, or sunflowers – are more exposed to water deficits and growth problems. "Within the agricultural seasonality itself, we will not have the same climatic reality." Therefore, continues Serge Zaka, "adaptation will have to occur at multiple scales: region by region, season by season."

The Challenge: Having Water at the Right Time

Beyond the total amount of water available, the central problem is its distribution over time. "Any intensification of the water cycle in both directions reduces the probability of having water at the right time. Either we will have too much water, or not enough," warns the climatologist.

Some plots are, for example, too wet to allow the spreading of fertilizers on wheat or rapeseed, while these crops need nitrogen at this vegetative stage.

A Race Against Time for the Soil

In this context, the soil becomes an essential lever for agricultural adaptation. "It’s almost a race against time for the soil," warns Serge Zaka.

Increasing organic matter improves the soil's ability to store water and cushion water variations. A question directly linked to the future of agriculture, he insists: "when we talk about food sovereignty and do not talk about the soil, it is a huge mistake. The soil is the foundation of food sovereignty."

The Clausius-Clapeyron Law, Key to the Water Cycle

Formulated in the 19th century by German physicist Rudolf Clausius (1822-1888) and French physicist Benoît Clapeyron (1799-1864), the Clausius-Clapeyron law describes the relationship between air temperature and its capacity to hold water vapor.

It shows that a warmer atmosphere can hold more water vapor. Specifically, each additional degree allows the air to hold about 7% more water vapor.

In a warming climate, the atmosphere stores more humidity. When this water vapor condenses, it can produce more intense precipitation.

This mechanism contributes to intensifying the water cycle:

1. more humidity available in the atmosphere;
2. rain episodes that are sometimes more intense;
3. but also drier periods when precipitation does not occur.