Commentary by Prescient Weather co-founder Richard James, Ph.D
Heat and Drought in Europe
Summer 2022 has brought widespread and severe drought to much of western, central, and southern Europe, including the United Kingdom, and episodes of record-breaking heat have compounded the impacts for many. In the UK, the all-time national temperature records were smashed for both daily maximum and highest daily minimum temperature, and July was extremely dry in southern England. Remarkably, according to the Met Office HadUKP data, the Southeast England region saw its driest July on record, with data back to 1873.
Climate Change Impacts on Drought?
When unusual climate anomalies like this occur, it is common to see broad assertions that climate change is at least partially responsible, or that extremes are more common or “more extreme” than they used to be. There is, of course, an enormous scientific literature on the response of weather and climate extremes to climate change, and it’s well-established that the role of climate change very much depends on the nature of the phenomenon.
For instance, there’s no doubt that the risk of exceeding high temperature thresholds is relatively much greater in the presence of a background warming trend: hot extremes have generally increased. On the other hand, there have been “small and non-significant changes” in meteorological drought in western and central Europe, and there are generally “inconsistent signals” for potential future changes (IPCC AR6 Chapter 11, page 1689).
Here’s an example of a Twitter comment on the dry July in England: commenting on the new color scale deployed by the UK Met Office (see screenshot below), the author says, “Traditional anomaly maps can’t cope with our new climate!” The author shall remain nameless, but with more than 20,000 followers this message was seen by quite a number of people. Is it reasonable to say that the “new climate” demands a new color scale? It was, after all, the driest July on record in southeastern England: the dryness was unprecedented for the time of year.
Drought in England Over Time
One way to answer the question of whether dry extremes (i.e., droughts) really have become more common (or more extreme) in England is to look at when the most unusual months have occurred over time. For instance, southeast England’s driest July was this year, but when were the driest June and August? According to the HadUKP data, these occurred in 1925 and 1940, respectively; and both of those months were in fact even drier than July of this year (1.3mm and 1.7mm respectively, compared to 4.2mm in July 2022). If we look at all months of the year, we find that 8 of the 12 record-driest months occurred in the first half of the history (1873-1947), and only 4 of 12 since then.
We can improve the sample size by looking at the “driest 3” or “driest 10” months; for example, which years had the driest 10 Julys? It turns out that half of the driest 10 Julys were pre-1947, and half since. Here’s a chart showing the occurrences of “driest 3” and “driest 10” months prior to 2022, again for southeast England. The total number of occurrences is, by definition, 36 for “driest 3” (12 months times the 3 driest in each case), and 120 for “driest 10”. To highlight any long-term trends, the solid lines show running 10-year averages of the annual counts.
It’s clear from the chart above that there hasn’t been a notable increase in very dry months for southeast England, and actually the occurrences of very dry months have been relatively sparse in the past 20 years. This is consistent with the IPCC conclusions about observed changes in meteorological drought.
England and Wales Drought: 250-year Comparison
More than a century of additional data is available in the HadUKP data for “England and Wales”, and the chart below shows the same analysis for the full 256-year history. Here we find a more striking result: in the past 60 years there have been only 2 calendar months in the “driest 3”; those months were August 1995 and May 2020. As extreme as July 2022 was in the southeast, it was “only” the 6th driest July for the England+Wales time series. Based on this data, we would be more justified to claim that dry extremes are diminishing rather than increasing.
Does this mean that wet extremes are increasing? Yes, the HadUKP data does show some support for that trend in the England+Wales series; see below for equivalent charts of “wettest 3” and “wettest 10” occurrences. For the England+Wales series, the increase in “wettest 10” months starting in 1912 is quite striking. And while the charts don’t deal with monthly records (i.e. “wettest 1”), 4 of the 12 monthly records have been set in the last 10 years (April and June 2012, January 2014, February 2020). This too is consistent with IPCC AR6, which expressed “medium confidence in the intensification of heavy precipitation” for western and central Europe and “high confidence” for northern Europe (Chapter 11, page 1685-1686).
In summary, although this summer’s drought was severe in the southern UK and indeed across much of Europe, it’s unwise to attribute all weather and climate extremes to anthropogenic climate change. Some classes of extremes, like drought in the UK, have not worsened over time, and undue alarmism tends to detract from objective efforts to both understand long-term change and predict extreme events when they occur.