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202312 Fresh Quarterly Issue 23 03 Extreme Is New Normal Web
Issue 23December 2023

Extreme is the new normal

Prof. Luca Corelli Grappadelli admiring South African pear orchards during the International Pear Symposium field day.
Bradley Urion
How climate change and extreme weather are impacting growers in Italy. By Anna Mouton.

Prof. Luca Corelli Grappadelli leads the Ecophysiology Laboratory in the Department of Agricultural and Food Sciences at the University of Bologna in Italy. His main research focus is the effect of environmental factors such as light and water on tree performance and fruit growth.

He visited South Africa for the International Pear Symposium earlier this year and spent a six-week sabbatical in the Department of Horticultural Science at Stellenbosch University, where he was testing new sensors in collaboration with Dr Sebinasi Dzikiti.

In a recent interview, Corelli Grappadelli shared the Italian experience of extreme weather and climate change.

Q. What are examples of recent extreme weather events in Italy?

Since I returned from South Africa, we’ve lost yet another crop to late frost. On 6 April, the minimum temperature was -8 °C. We might never reach -8 °C here in winter, even with snow on the ground. Last year, we were frosted on 26 April — the second-latest frost in my lifetime.

Historically, we’ve been threatened by frosts until 10 April, so people will look at this year and say it’s normal. But they forget that we’ve been frosted out in the last three of four years. And we had another partial and a total loss from frost damage in the three or four years before that.

Then, at the end of April, we were experiencing a drought that had carried on from the previous summer — we had no winter rains. In our region, irrigation starts in May or even June, but on 27 or 28 April, I was in a grower’s meeting where the topic was how to cope with drought.

Fast-forward a few days, and on 3 May, we were under the first of the two floods in the Romagna region this year.

Once the water ran away, we had drought again because most of the water was not absorbed. Summer ensued with high temperatures. We had almost two weeks of non-stop warm days where temperatures got into the forties. We’ve seen 41 °C and 42 °C before, but not for a two-week stretch.

Q. How did the extreme weather affect orchards?

It is too soon to tell what the damage to orchards has been, but several kiwi-fruit orchards have been grubbed because the vines were dying. And I was looking at some peaches yesterday where the leaves were uncharacteristically yellow for September when they should still be actively photosynthesising.

We think several days of root anoxia probably damaged the kiwi’s root systems. Then, the high summer temperatures led to a strong demand for water for transpiration, and the root systems could not cope, so the canopies started to die back. And the peaches might be showing us a similar problem.

In many places where rivers broke levies, they discharged clay layers up to 500 mm thick. Some growers pushed it out of their orchards, but others didn’t because it was less thick or unaffordable — farmers are not doing too well economically, and now they’ve also lost a crop. So, we are waiting to see what happens. It looks like some orchards will be hurt by losing soil fertility.

It seems this is the new normal. We go from drought to flood — from one extreme to the next.

People say the earth has undergone periods like this before. The earth has survived and will survive — for the earth, climate change is just a blip. But for humanity, it can be a disaster, yet people fail to realise this.

Q. What longer-term impacts are you seeing on orchards?

We have mild winters. September and October are the nicest months — we used to like July and August, but now those are too hot and sunny. And rainfall seems to be concentrated in November.

Dry and mild winters are not like it used to be. So now we have the same difficulties as South Africa with winter chill. For crops like peaches and nectarines, where we have low-chill cultivars, we still satisfy their chill requirements, but then February is warm enough that the trees start blooming. And if trees flower early, it’s a cinch that frost will hit them.

The shallow winters followed by early flowering and a bigger window of opportunity for serious frost damage is, to my mind, the worst effect of climate change on our agriculture. We need to improve our water reservoirs, but up to now, I don’t think summer heat has been the worst problem.

In apples, we’ve observed quite different full-bloom dates depending on the cultivar’s chill requirement. This creates problems because cultivars that are supposed to pollinate one another don’t overlap. And then flowering in some cultivars is so protracted that there are different size classes of fruit on the tree.

Q. Does your research include ways to cope with climate change?

Definitely. My angle is controlling and reducing water use because we’re under water restrictions, and we don’t see any improvement in that situation. We can’t expect more water resources, so one strong part of my programme addresses this.

Our solution so far has been to reduce light levels in the orchard by shading materials. Reducing sunlight will not hurt photosynthesis and fruit growth in apples, although colour pigment formation is another story.

For crops like peaches, where we cannot simply remove light, we’ll still remove some light, but we’ll have to be less aggressive, and we would have to achieve the remainder of the water savings through controlled deficit irrigation.

We need less direct energy supplied to the leaves. When I spend time in our cordon orchard, it seems that the trees shade each other by being so close together yet so narrow, but light still seeps in from all directions. I would have to measure it, but very narrow canopies do seem to provide a smart way of self-shading in apples.

Even if we stop putting greenhouse gases in the atmosphere today, the carry-on effect will last for decades. We can’t continue doing the same things while we wait for that to abate. We need to revolutionise the way we grow fruit.

Hortgro interviewed Prof. Luca Corelli Grappadelli when he visited South Africa in January 2023. Read his thoughts on the digital orchard in the April issue of the SAFJ.

Bonus: Extreme weather in a climate context

Severe flooding occurred in May 2023 in the Emilia-Romagna region in Italy. The region received about as much rain in two weeks as usually falls in seven months. Some areas received almost half their annual rainfall in 36 hours.

The floods caused 17 deaths and displaced approximately 50 000 people. The final cost of the damage is as yet unknown, and the psychological impact is impossible to quantify.

An analysis by the academic collaboration group World Weather Attribution concluded that the Emilia-Romagna floods did not directly result from climate change. But the group has shown that climate change is linked to similar events, such as the July 2021 floods that killed at least 222 people in Belgium and Germany.

World Weather Attribution also found that widespread frost damage to hundreds of thousands of hectares of French fruit trees and grapevines in April 2021 was exacerbated by climate change. An abnormally warm March prompted earlier bud break, followed by temperatures below -5 °C in early April.

The past summer saw extreme heat in much of the Northern Hemisphere. July 2023 was the hottest month since records began. Research on ancient sediment and ice samples suggests it was the hottest month in 120 000 years.

World Weather Attribution reported that the maximum heat Southern Europe experienced in 2023 would have been near impossible without climate change — Europeans can now expect similar heatwaves in one out of 10 years, and the frequency will rise as the world warms further.

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