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Heatwave: What is causing it and how are people and the countryside in Wales being affected

11 Aug 2022 9 minute read
The River Tawe, north of Pontardawe, in July. Photo by Richard Youle

 Richard Youle, local democracy reporter

Monthly bulletins about river, groundwater, reservoir and soil moisture levels may not quicken the pulse, but they might start attracting a wider readership if the persistent dry conditions in much of England and Wales continue.

The UK’s National Hydrological Monitoring Programme provides a stream of monthly data – its bulletin for July is due out on this coming Friday. Recent ones have referenced a general shortage of rainfall since last autumn, and a trend of dry spring months in recent years.

The bulletin for June, published early last month, included a sentence which has turned out to set the scene for what has unfolded in much of England and Wales.

“With river flows, groundwater levels and reservoir stocks widely below average, and current outlooks favouring a continuation of this situation, there is a heightened risk of impacts on agriculture, the environment and water supplies in the coming months – hot, dry weather in early July further adds to this prospect,” it said. Reservoir stocks in Wales, it added, were the lowest recorded for the month of June.

And all this before the heatwave which smashed records in Wales, England and Scotland.

Under stress

While the benefits of the dry and hot weather for holiday-makers and families with children during the summer break are welcome, the countryside is under stress. As is much of Western Europe, notably France – a major food producer.

A spokesman for the UK Centre for Ecology and Hydrology, one of two organisations which compiles the monthly bulletins, told the Local Democracy Reporting Service that the impacts of these drought-like conditions in the UK included a reduction in soil quality, peat and moorlands drying out, habitat loss, wildfires, tree and vegetation death – even localised extinctions.

Some trees may even shed whole branches as a defence mechanism, according to an expert at the Royal Botanic Gardens, Kew, London. Kevin Martin, head of tree collections at Kew, said this was known as summer or sudden branch drop. Many species can suffer from this, he said, including beech, oak, cedar, sweet chestnut and horse chestnut.

Mr Martin said trees had various mechanisms to cope with prolonged dry conditions, such as dropping leaves earlier than normal and relying on stored energy from spring and early summer. He said they could also control water loss by closing stomata – minute pores – in their leaves.

When it came to unusual heat, Mr Martin said trees had different traits depending on their natural distribution. Those which dealt with more regular heat stress normally had leaves with thicker and hairy undersides, and branches in a layering formation to protect the inner, shaded section.

With mass tree-planting Government policy in Wales and the UK, Mr Martin said Kew Gardens, which has a collection of 14,000 trees, was observing which species were better suited to hot, dry conditions and which were not.

“I would say trees which come from the Mediterranean zone and eastern Asian area are best adapted to deal with heat and drought stress,” he said. Species which were becoming unsuitable, he added, included silver birch and common beech.

Asked if trees which were less suited to prolonged dry and hot conditions recovered quickly when rainfall returned and temperatures decreased, he said: “Unfortunately not. The damage caused by the current conditions will have long-term impact.”

Mr Martin said this was particularly in terms of damage caused to the tree vascular system, which carries water water and minerals from the roots to the leaves and photosynthesised food back down.

Trees, like this one in Singleton Park, Swansea, have coping mechanisms to deal with prolonged dry weather. Photo Richard Youle


Farmers’ union NFU Cymru said the negative effects of the current conditions probably outweighed the benefits, although it stressed there were large regional variations.

A union spokesman said there was more certainty in terms of harvesting wheat and corn, but that soil moisture reduction could impact yield quality. He said it was very unlikely that anyone will be able to get crops planted back in the ground at present, and that the current conditions were of particular concern to horticultural growers, with potatoes among the crops affected.

“The main concern for livestock farmers at present is the welfare of their animals,” said the spokesman. Grass growth was a major concern for many areas of Wales, with many farmers likely to use winter forage early.

The spokesman said some farmers who relied on boreholes and natural springs may have to start getting water from elsewhere. He added that farmers in Wales were working towards an NFU Cymru “net zero” target by 2040 – a core element of which was to become more efficient. “Many farms would like to store more water and it’s important that planning systems enable this to happen,” he said.

Tom Rees, of Pembrokeshire, farms 1,200 acres – three-quarters of which is for combined crops such as wheat, barley and oil seed rape. Apart from 50 acres of potatoes, the rest is woodland and grass.

“It has been very, very dry since almost this time last year, apart from sporadic downpours last September and October,” he said.

However, he said the conditions have been very favourable for his arable crops thanks to just enough rain top-ups coming at the right time.


“The harvest has been unprecedented – it’s never as been as early as this before,” said the 34-year-old. “The yield doesn’t doesn’t seem to be too bad. We’re also getting high-quality straw in large volumes.”

The overall rainfall shortage has badly affected his potatoes though. The farm’s irrigation ponds ran dry in June, although there is still a couple of feet of water in them to support ducks and other wildlife.

Mr Rees said rainfall normally recharged the ponds, but not in recent weeks. “I should think the water table is out of sight,” he said.

He said he expected to get 15 to 18 tonnes of potatoes per acre this summer, compared to 25 tonnes in a normal year. Shoppers may start seeing smaller potatoes, carrots and onions on the shelves in the coming months.

Mr Rees said the next oil seed rape crop needed planting shortly and that rain was needed to boost low soil moisture levels. “That”s really important,” he said. “There’s quite a shortage of oil seed crops – Ukraine was a massive exporter of sunflowers (for sunflower oil).”

Jet stream

High pressure systems have dominated the weather in much of the UK and western Europe of late, bringing bone dry conditions and heatwaves. The jet stream – a west-to-east river of air five to seven miles above the Earth’s surface which tends to usher in unsettled weather – has largely passed to the north. This in itself is not unusual for the summer, the Met Office said.

The jet stream in the northern hemisphere largely exists due to a difference in heat between cold air on the northern side – towards the Arctic – and warm air to the south. The Met Office said the seasons also affected the position of the jet stream. In winter there is more of a temperature difference, hence the jet stream is stronger and flows across the UK.

As temperatures in the Arctic are rising faster than elsewhere in the world, could this mean that the jet stream itself will move north in the summer because the temperature difference needed in its formation moves in that direction? It is a theory which has received attention.

Met Office climate scientist Adam Scaife said it was correct that the jet stream had moved north this summer and that the Arctic was warming around three times faster than the rest of the planet. But he said these two things were not connected.

“It’s not that it’s impossible, but the early studies were very speculative,” he said. “I would not attribute this summer to the warming of the Arctic.”

He said the latest evidence was that, if anything, the jet stream should move south in response to Arctic warming. Prof Scaife also said there were also effects on our summers connected to the Atlantic Ocean.

He added that once the jet stream did move, small-scale weather patterns helped to keep it “locked in”, which helped to explain why we get persistent wet or dry summers.


The Met Office said fierce heatwaves have occurred this summer in China and parts of the USA – particular the south-west – as well as Western Europe. It said many of these events were connected by a naturally-occurring pattern in the atmosphere, known as wavenumber 5 pattern. It said it was monitoring this pattern very closely.

What is the role of climate change in all this, the Met Office asked in a blog?  “The extreme temperatures that we have been experiencing in the UK are unprecedented in recorded history,” it said. “In a climate unaffected by human influence, climate modelling shows that it is virtually impossible for temperatures in the UK to reach 40C.”

The persistent dry conditions were compounding localised effects, it said. “When the sun shines on the ground, dry soils cannot release energy through evaporation of moisture, which means that more of the sun’s energy goes into heating the air, further amplifying the temperatures in the UK.”

It said the wavenumber 5 pattern, climate change and soil moisture feedback had come together in the UK and made temperatures of 40C possible.


Rivers in Wales are feeling the strain. The Wye and Usk Foundation, which restores and protects the ecology and fisheries of the Wye and Usk rivers, said low water levels were combining with  higher than normal evaporation rates. This concentrated river nutrients, whatever their source, and could in turn provide ideal conditions for algae to bloom and deprive aquatic life of vital oxygen.

The environmental charity said high water temperatures stressed fish, making them more vulnerable to illness. A spokeswoman said some sections of river have even dried up, extinguishing any aquatic life which would have existed before.

She said: “The whole of Wales and its river courses are suffering at present with some in more difficulty than others. The ongoing low levels of precipitation across Wales in June and July have meant that no area is operating at normal water levels at present. ”

She said low water levels also posed problems for agriculture and industrial sectors which abstracted water from rivers.

“The river ecosystem, once stressed by low water levels and the knock-on effects that these have in a heatwave, will take substantial time to recover without sustained precipitation and more moderate temperatures,” she said.

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