It was climate change wot gave us such a wet and stormy winter – or so you may have gathered from various reports this week. ‘Never ending UK rain made ten times more likely by climate change,’ declared a Guardian headline. ‘Climate change is a major reason why the UK suffered such a waterlogged winter, scientists have confirmed,’ asserted the BBC. There have also been numerous references to a ‘record stormy winter’ – based on it having the highest number of named storms in, er, the nine years since the Met Office started naming storms.
We hear endlessly about the costs of flooding, but not at all about the savings from the declining incidence of strong winds
But how much of this reflects reality? The reports were based on the publication of the latest analysis by something called World Weather Attribution – a Netherlands-based initiative which attempts to link particular adverse weather events to climate change, by running climate models. But the report into Britain’s wet and stormy winter also lays out the actual real-world data going back several decades. What does it tell us? That UK winters are getting wetter but also – contrary to what you may have heard asserted in the past few months – less stormy. Depending on what metric you use to measures storminess – the occurrence of 40 knot, 50 knot or 60 knot winds, or an amalgamated measure known as the Storm Severity Index (SSI) – the winter just passed was the stormiest since only 2021 or 2016. By the standards of the 1980s or early 1990s it would have been a calm winter.
The decline in storminess is all stated in the report, and even makes it into a paragraph in World Weather Attribution’s press release, but seems to have dropped out of the reporting. We hear endlessly about the costs of flooding, but not at all about the savings from the declining incidence of strong winds.
As regards rainfall, an increase is consistent with a warming climate as warm air can contain more moisture – which is why the wettest places in the world tend to be in the tropics rather than the Arctic. But higher rainfall doesn’t necessarily translate into greater flood risk as warmer air also increases evaporation, which promotes the drying-out of ground between rainfall events and means that rain is likely to be falling on less-saturated ground. As for data on actual flows of flood water this tends to be rather sparse, and doesn’t feature in World Weather Attribution’s study.
But what about the modelling, which gives rise to headlines such as that claiming that the wet winter of 2023/24 was made ‘ten times more likely’ by climate change? As with previous World Weather Attribution studies, the latest one reveals a huge gulf in modelled predictions. One model predicts that the warming of the planet since ‘pre-industrial’ times (by which it means late 19thcentury) should have increased rainfall intensity on stormy days during the UK winter by 32 per cent, another predicts that it should have decreased intensity by 17 per cent. In this case the real-world observational data suggests that there has been an increase of 35 per cent – higher than any of the models. The study comes up with claim that climate change made rainfall ‘about 20 per cent heavier’ by combining these figures to make an average.
What does the extraordinary spread of predictions in the models tell us? That climate models are not nearly robust enough to allow anyone to quantify the increased risk of winter rainfall in Britain. Indeed, scientists undertaking previous studies for World Weather Attribution have declined to quantify increased risks for this very reason. This does not, however, seem to prevent the media lapping up the headlines which World Weather Attribution feeds them. Sadly few reporters, I fear, may get round to reading the actual reports.
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