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WEATHER

Reader question: Why are the leaves falling in summer and does that mean my garden is dead?

It might look like fall outside in certain parts of France, but it certainly feels like summer. So why are the leaves falling from the trees? And what does that mean for your garden?

Reader question: Why are the leaves falling in summer and does that mean my garden is dead?
This photograph taken on August 3, 2022, shows early fall of leaves at the Buttes chaumont park in Paris as France experiences a heatwave. (Photo by BERTRAND GUAY / AFP)

Reader question: It’s only the middle of August and already the leaves have fallen from most of the trees – my lawn is covered with dead leaves like it’s the middle of autumn. Why is this happening and does it mean the trees are dead?

France is having a hot, dry summer and humans and animals are not the only ones suffering amid the heat. Plants and trees are looking pretty sickly in many areas and you may have noticed an unexpected sprinkling of dead leaves on the ground – one that you might normally expect for the fall months. 

The short answer is that the trees are thirsty too. As a result of a lack of water, trees can lose their foliage, but if you’re a gardener you don’t have to worry too much: this is a self-protection mechanism. 

While seeing leaves falling in early August might be surprising to you, it actually is a natural reaction from trees that are just trying to protect themselves from high temperatures. 

Nathalie Breda, the director for research at the National Research Institute for Agriculture, Food and Environment (INRAE),  said trees are a lot like humans when it comes to heat: they sweat when it is hot.

“Transpiring is an active part of temperature regulation,” said Nathalie Bréda to French radio service FranceInter. “This is the first step the tree takes when the temperature is high – it pumps water through its roots, which eventually turns into water vapour once it reaches the foliage, later being released into the atmosphere.

“The tree will pump water through its roots, which will turn into vapour once it reaches the foliage, and which will be released into the atmosphere.”

This helps to keep the tree at a lower temperature than the air. The tree does this by ‘opening its stomata’ (similar to pores) – which allows the plant to release water. 

However, once temperatures get even higher, and there is less water for trees to draw upon, then they ‘sweat’ less. 

“Once the tree feels that there is less water in the soil, it limits the opening of the stomata to conserve water and preserve itself,” said Bréda. 

This means that the tree gives up on its foliage to help conserve water, causing the leaves dry out and fall to the ground. 

Do gardeners have to be worried?

While conserving water in this way can weaken the tree in the long term, it does not mean that the tree dropping leaves in your garden is dead. Most trees should recover, even if it takes several years after a drought to do so (as it did, for instance, with the years 1976 and 2003).

Trees shed their leaves in the fall when they sense cold, unsuitable weather is coming. It is the same principle where they seek to conserve water and energy. 

That being said, when the tree loses leaves prematurely, this means it has finished growing prematurely for that season. Practically, trees need to open their stomata in order to photosynthesise, as this is the part of the tree that allows the entry of carbon dioxide. Failing to do this can put the tree at risk, as the plant needs to photosynthesise to remain healthy and protect itself against insect attacks and frost waves. 

Bréda explained to FranceInter that “after the 2018 heat wave, all the spruce trees in Eastern France were killed by bark beetle insects. This happened because they were weakened.”

It also takes plants one or two seasons to be able to recover and build back up their reserves. Experts worry that with recurrent climatic distress, the plants will not “have the time to recover from one year to the next.”

A sign that the tree is suffering amid severe drought might be ‘weight loss,’ Bréda explained to FranceBleu. “When drought becomes very severe, we even see that trees lose weight. Meaning, they use the water in their elastic tissue to compensate for the lack of water in the soil.”

What can I do to protect my trees?

For gardeners or home owners looking to protect their trees, another idea is to trim the branches back – this would allow them to reduce their foliage and better conserve their water. The quick answer would typically be to simply water the tree, but with most of France on some level of drought alert – water restrictions are in place almost everywhere across l’Hexagon. 

READ MORE: MAP: Where in France are there water restrictions and what do they mean?

For urban areas, Bréda recommends that cities reconsider the way of planting vegetation in the city: it is necessary to “review the size of the tree planting hole, and move the road (asphalt) away from its roots a little. This would allow the soil around it to better rehydrate when it rains.”

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PARIS 2024 OLYMPICS

How hot will it be in Paris during the Olympics?

A recent report has warned of the dangers of extreme heat for athletes - but what should spectators expect if they are in Paris for the Olympics or Paralympics?

How hot will it be in Paris during the Olympics?

The report labelled Rings of Fire – a collaboration between non-profit Climate Central, academics at Britain’s University of Portsmouth and 11 Olympians – warned that “intense heat at the Paris Olympics in July-August 2024 could lead to competitors collapsing and in worst case scenarios dying during the Games.”

Closer examination, however, reveals that the warning is based on previous heatwave scenarios in Paris, rather than any specific predictions for this summer.

Still, Paris can get pretty hot – so what should Olympics visitors expect this summer?

Seasonal norms

Held between July 26th and August 11th (Olympics) and August 28th and September 8th (Paralympics), there’s no doubt that the Games fall into the hottest part of the French summer.

Average temperatures in Paris for July and August are between 16C and 26C, falling slightly in September to 13C/22C. 

However, when the city is in the grip of a canicule (heatwave) temperatures can rise significantly – the highest temperature ever recorded in Paris was during a heatwave in July 2019 – it was 42.6C.

During a heatwave it’s not uncommon for temperatures to be in the high 30s and to sometimes hit 40C.

Heatwaves usually don’t last long – they are officially defined as days with hot temperatures which also see little fall in the temperature at night (the ‘tropical night’ effect) and it’s rare to have more than five consecutive days like this.

One extra thing to take into account is the ‘heat sink’ effect – the effect that makes cities hotter than the surrounding areas. This happens to an extent in all cities as the cumulative heat exuded from people, vehicles and machinery (especially air-conditioning units) raises the temperature.

It is especially pronounced in Paris, however, due to the geography which traps the heat and the fact that Paris is a city with very little green space – during a heatwave the city can be up to 10C hotter than the surrounding countryside.

Forecast for summer 2024 

The especially annoying thing about heatwaves is that weather forecasters can only predict them about a week in advance, so at present we have no way of knowing whether the weather will be normally warm or insanely hot during the Games period.

French weather forecaster Météo France has predicted hotter-than-average temperatures over the whole of the summer, but cannot predict individual weeks this far in advance.

So far the year has been unusually rainy with cooler than normal temperatures, although the sunshine has returned this week. 

So how should Games visitors prepare?

If you’re attending events within the city, be aware that not all the stands have shade so you should prepare for your event by using a high-factor sunscreen (factor 50 preferably) and take a hat that provides shade for your face and the back of your neck. Stay hydrated.

Loose-fitting, roomy clothing made from natural fibres (eg cotton or linen) will be the most comfortable.

Other than that – keep an eye on weather forecasts and warnings.

If a heatwave is predicted, weather warnings (ranging from yellow ‘be prepared’ to red ‘possible danger to life’) will be issued, along with advice on keeping yourself safe.

The city will also activate its heatwave plan if temperatures soar – this includes setting up brumisateurs (machines providing cooled water vapour) and showing a map of ‘cool rooms’ within the city. There are also provisions in place for elderly or ill people who are more vulnerable to high temperatures.

Even outside a heatwave period Paris has a network of drinking water fountains to enable you to stay hydrated.

Take the warnings seriously – every year people die due to heatwaves

READ ALSO The French government advice for staying cool in a heatwave

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