Chief Hydrologist Duncan Faulkner reflects on the latest research into the unusually dry Aprils experienced across Europe

To mark the start of Waterwise’s Water Saving Week, which runs from 23-27 May, JBA Chief Hydrologist Duncan Faulkner reviews the latest research and evidence that seeks to explain the series of unusually dry Aprils witnessed across much of Europe.

When did you last reach down and pick up a handful of soil?  If it was during last month, April, you will probably have noticed how dry it was. Water butts were being emptied across the land as gardeners kept their newly sown or planted seedlings supplied with moisture. In most of England and Wales, less than half the average amount of rain fell in April. The dryness was exacerbated by an increase in potential evapotranspiration due to temperatures being 0.5 to 2.5°C above the 1961-90 average across all of the UK.

April 2022 was the latest in a series of unusually dry Aprils across not just the UK but a large area of Europe. A paper by Monica Ionita et al. (2020) in npj Climate and Atmospheric Science looked into the curious case of dry Aprils across central Europe since 2007. It presents the maps above, which show anomalies in (a) precipitation and (b) mean temperature for Aprils in the period 2007-2020. While the precipitation anomaly is strongest in central Europe, it is also evident across much of the UK. The temperature anomaly covers all of Europe.

Using UKCEH’s excellent UK Water Resources Portal we have produced maps of standardised precipitation index for April over the UK for the years 2017 to 2022.  They show that most of the last six Aprils have been unusually dry in most parts of the UK. April 2018 was the main exception to this rule, although an extremely dry few months followed it. The maps also show that the far north of Scotland can often be different from the rest of the UK at this time of the year.

Figure 2

It does seem to be the month of April in particular in which the rain takes a break. Ionita et al., looking at central Europe, find no similar trend in March or May. We have found that the situation is similar in much of the UK. Figure 2 shows the series of rainfall at Cambridge for each month. The black line is a 7-year moving average, which helps visualise the decline in April rainfall since the year 2000.

Figure 3

A statistical trend test gives a more objective assessment. Figure 3 shows the result of the Mann-Kendall test for trends in the rainfall for each month at Cambridge. Positive scores indicate an upward trend over the period 1960-2022 and vice versa. It is only in April that the null hypothesis of no trend can be rejected at a 5% significance level.

We repeated this analysis at other sites with long-term rainfall data, sticking with the period 1960-2022. We found significant negative trends in April rainfall in the north of England (Bradford) and Northern Ireland (Armagh). Trends were negative but less marked in the west of England (Ross on Wye) and Scotland (Paisley).

Ionita et al. found that the unusually low rainfall and high temperatures in April were triggered by the presence of blocking high-pressure systems centred over the North Sea and northern Germany, and a decline in the temperature gradient between the Arctic and mid-latitudes.  These act to divert the Atlantic storm tracks further northward than usual – which may help explain why the far north of Scotland does not always share in the dry weather. The Met Office give a similar explanation for this year’s dry April in the UK.

Want to know more?

For more on this subject make sure to read Duncan’s follow up blog, which will consider the implications of April’s dry weather for water users. To find out more about Waterwise and Water Saving Week visit the Waterwise website.

Further details of our Water Resource Management services can also be found here.

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