Despite central England temperature series being a composite temperature from three separate sites, it’s still possible to use the UKMOUKMOThe Meteorological Office is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy 25°C heatwave temperature as the threshold to calculate a heatwave day in Central England, and thereby calculate the number of three day consecutive days that have occurred there since 1878. I added this functionality to my Daily CETCETCentral England Temperature application a number of years ago, and have recently added a second method of using the maximum anomaly to do it, rather than by using a fixed temperature. At the same time I gave it all a bit of a spring clean, hopefully it’s still accurate. 🤞 The program allows you to adjust the threshold from 25°C to 30°C, and the anomaly from +6°C to +10°C, it also allows you to change the number of consecutive days from 3 to 7.
If you plot a bar chart for the number of heatwave days since 1878, as I’ve done with an accompanying 5 year centred average and linear trend, you’ll see that the number of days >=25°C has increased from 4.6 days to 10.8 days in the intervening 146 years.
The most number of distinct heatwaves (using the 25°C and three consecutive days or more rule) in a single year was six and occurred in both 1911 and 1995. The most number of heatwave days in any one year was 33, and occurred in 1976 and 1995.
The longest heatwave I found, using the 25°C and three consecutive days or more rule, was 16 days which occurred in the golden summer of 1976, between the 23rd of June and the 8th of July 1976 this was closely followed by the 15 day heatwave covering an almost identical period in 2018.
The results using anomalies are a horse of a different colour and a story for another day. Suffice it to say I used the 1878-2023 LTALTALong Term Average. This is usually defined as a 30 year period by the WMO. as a level playing field to produce the results in the table below. The year 1995 still ends up with most heatwave days of 32, and 1976 the longest run of anomalies of 6°C and higher of 16 days.
Is it possible to get a heatwave in Spring? I beleive it is, and it seems to have already happened at least once since the start of astronomical spring in central Europe. I reckon that maximum temperatures anomalies of 10°C above the LTALTALong Term Average. This is usually defined as a 30 year period by the WMO. constitute a heatwave day. The definition of a heatwave of course is that these high temperatures should occur for at least three consecutive days or more. So the charts I’ve constructed are just a simple count of days with anomalies higher than 10°C. I’ve not any deep research into this, but have just added a chart for 2023 for a comparison. I think, like a lot of others do, that with global surface temperatures and North Atlantic SSTSSTSea Surface Temperatures being at unprecedented high levels as they are at present this is portentous, and summer across mainland Europe could see a record number of severe heatwave events and the risks that this brings. Hopefully I’m proved wrong, and surges of warm air flooding up from the tropics won’t occur too frequently.
The exceptional heatwave across Belarus, Ukraine & E Russia continued this lunchtime, with anomalies as high as +19°C, the highest I’ve seen. Juxtaposed with the very cold air across Finland, Sweden and northern Norway.
I have added a new viewer to my SYNOPSYNOPSYNOP (surface synoptic observations) is a numerical code (called FM-12 by WMO) used for reporting weather observations made by manned and automated weather stations. SYNOP reports are typically mad hourly and consist of groups of numbers (and slashes where data is not available) describing general weather information, such as the temperature, barometric pressure and visibility at a weather station. climate application to display estimated daily temperatures for the whole of the UKUKThe United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and Northern Ireland.. I use as many daily reported maximum and minimum temperatures from WMOWMOThe World Meteorological Organisation is a specialized agency of the United Nations responsible for promoting international cooperation on atmospheric science, climatology, hydrology and geophysics. stations 03001 to 03950 as I can to calculate a UK mean for all stations below 250 M amslAMSLThe height Above Mean Sea Level.. That equates to around 120 observations each day. Nowhere near as accurate as the 1 km x 1 km gridded estimates from the UKMOUKMOThe Meteorological Office is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy, but good enough for me. As you can see it picks out the two heatwaves that have occurred this year. It does look like my estimates maybe just two high though, because mean temperatures in both July and August were much close to average than this. That’s not really that surprising because its totally dependent on an even spread of site location, but they tend to be further south and coastal sites. I suppose that I could use all available sites, even those on mountains, and adjust their temperatures down to sea level.
It’s slightly difficult to gauge the number of heatwaves in Central England. One of the reasons for that is the CETCETCentral England Temperature series is made up of a composite temperature from three separate sites, the other is that the series extend back so far, 1878 in this case, that choosing a fixed value for the whole of the last 145 years is problematic because of increases due to global warming. My DCET application allows the user to define which threshold to use and it’s length. In the example above the application displays all heatwaves of three consecutive days or longer, with maximum daily temperatures of 25°C or higher. The UKMOUKMOThe Meteorological Office is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy current criteria for heatwaves is 25°C for a large part of the UKUKThe United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and Northern Ireland.. Of the three sites that are used to calculate a composite temperature for central England at the moment, one of them Stonyhurst is in the 25°C region, the main one Rothamsted, is in the 28°C region, and the other Pershore, is in the 27°C region. So you could argue I should use the weighted average of the three 27°C but what the hell. The longest heatwave in Central England lasted for 16 days, from the 23rd of June to the 8th of July 1976. That’s one day longer than the 15 days of 2018 for similar dates. The earliest heatwave in the series back to 1878 if I’ve done my programming correctly was from the three days from the 28th to the 30th of May 1944. The latest heatwave was the three days that started on the 29th of September and lasted to the 1st of October 2011. I’ve catalogued 145 individual heatwaves in 145 years which is a bit of a coincidence and not a lot of people know that. The recent record breaking heatwave for September (2023) that’s just finished (and here I’m assuming it finished on the 10th) lasted for seven days from the 4th to the 10th of September, which makes it the joint fifth longest heatwave in the series to date, in fact it equals the seven day heatwave that occurred earlier in the year in June.
Are heatwaves getting more common?
Yes, of course heatwaves are getting more common, CET temperatures have been rising at the rate of 0.254°C per decade for the last 50 years, so they are bound to get more frequent and longer lasting. The chart below gives you an idea of the increase, it displays a bar chart of the annual number of days when daily maximum CET exceeds 25°C. I have added a 10 year centred average to the chart, and also a linear trend from 1878 to 2023. A shorter trend would show a much larger rise than the 0.4 days/decade increase than this trend shows but I am starting to flag and it’s getting near to dinner.
What surprised me about temperatures in July 2023 was how the media went on a frenzy and adopted what was a North African heatwave and described it as an whole encompassing European affair, when mean temperatures across a large part of the continent for much of the month were below average.🤔
Courtesy Copernicus- the picture that caused all the fuss
Just a quick look back at the heatwave of July 2023 across the Mediterranean. There was a great deal of interest in this taken by the media in the UKUKThe United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and Northern Ireland., particularly the BBCBBCThe British Broadcasting Corporation (BBC) is the national broadcaster of the United Kingdom, based at Broadcasting House in London. It is the world's oldest national broadcaster, and the largest broadcaster in the world by number of employees, employing over 22,000 staff in total, of whom approximately 19,000 are in public-sector broadcasting.. As far as I can see it was in my opinion, and that’s what this blog is all about, was sparked off initially by some overzealous reporting by the new (to me) Rome correspondent who was interviewing a selection of British tourists in the centre of Rome in the middle of a hot sunny day. I think this was in reaction to a warning from METEOAMMeteoAMThe Italian Meteorological Service is an organizational unit of the Italian Air Force (Servizio Meteorologico dell'Aeronautica Militare) and the national meteorological service in Italy. The weather forecasts and other services serve both the armed forces and the general public. of a severe heatwave dubbed Cerberus on the 13th. If you’ve ever been to Italy or abroad you’ll realise it’s usually a good idea to hide from the sun at this time of the day😉 As far as I can ascertain from observational data there was a short 3 day heatwave (see thermograph below) at Rome’s airport. The trouble with observational data from Italy, as is the case in the UK, you can only access a subset of it, and unfortunately Rome has only one SYNOPSYNOPSYNOP (surface synoptic observations) is a numerical code (called FM-12 by WMO) used for reporting weather observations made by manned and automated weather stations. SYNOP reports are typically mad hourly and consist of groups of numbers (and slashes where data is not available) describing general weather information, such as the temperature, barometric pressure and visibility at a weather station. station situated at the airport on the coast. Because of the HIEUHIUrban Heat Island (UHI) is an urban area that is significantly warmer than its surrounding rural areas due to human activities. The temperature difference is usually larger at night than during the day, and is most apparent when winds are weak. UHI is most noticeable during the summer and winter. The main cause of the UHI effect is from the modification of land surfaces I’m sure it was much warmer in the centre of Rome. Not only is there a shortage of observational data for many countries, I challenge you to find any up to date LTALTALong Term Average. This is usually defined as a 30 year period by the WMO. climate data for any of them either. What I mean here by up to date is the LTA for 1991-2020 and not that for 1971-2000 that I have for many stations. You would have thought in these days of “global boiling” the latest climate station for all member countries would be available on the WMOWMOThe World Meteorological Organisation is a specialized agency of the United Nations responsible for promoting international cooperation on atmospheric science, climatology, hydrology and geophysics. website – no it isn’t – and if it wasn’t for Wikipedia, and some nifty parsing, I wouldn’t have collected over 800 LTA records across the world as I have. I’ve been watching and examining heatwaves closely across the UK and Europe since I retired from the Met OfficeUKMOThe Meteorological Office is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy in 2011. There are no rules as to what constitutes a heatwave, and therein lies the problem. The UK have one set of rules and every other country has another, and that’s why I argued, mainly to myself because few people read what my views are or give a damn about them either, that instead of a rigid threshold for summer months of X°C for a region, as the UKMOUKMOThe Meteorological Office is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy do, a “heatwave day” should be defined on the anomaly of the maximum temperature for each individual station. Over the years I’ve developed software and I usually default to an anomaly of 6°C above the LTA. Personally I think this is much too low for a severe heatwave, and probably should be ~+10°C. The thermograph for Seville shows the extent of the heatwave there using this 6°C rule. Three distinct heatwave days up to the 28th. These anomalies are calculated using the 1981-2010 LTA and not the much colder LTA of 1971-2000.
Seville 1981-2010 LTA
These thermographs for Rome, Decimomannu and Palermo use the 1971-2000 LTA. and because they anomalies calculated using this slightly colder LTA, the anomalies are much warmer than if I had the ones for 1991-2020. I’ve emailed METEOAM to see if I can obtain them, but am not hopeful I will be able to source the latest climate data. I shouldn’t need to do this, or rely on Wikipedia to supply them, this basic climatological data should be available from the WMO. That aside the three thermographs do highlight a series of heatwave days, with many as 15 at Decimomannu in Sardinia with an extreme maximum of 46.8°C.
I hope I’ve explained the importance of using the latest LTA for all stations to get an unbiased picture of July’s heatwave. The map below of total heatwave days shows the number of days with a maximum temperature anomaly of 6°C or higher. There’s no doubt that it was hot across a large of southeastern Europe using the +6°C threshold, particularly across parts of northern Algeria and Tunisia. There are what looks like spuriously high anomalies scattered around these are probably caused by out-of-date LTA.
Number of days with a maximum temperature [06-18] >=+6°C
If you look at the next chart this shows the total number of days with anomalies of +10°C or more, and what I maintain are severe heatwave days. Heatwaves in the UK must last at least three consecutive days or more before they can be officially labelled a heatwave, many of the sites in the chart below away from North Africa have one or two, and even if they have more they may not be consecutive.
Number of days with a maximum temperature [06-18] >=+10°C
Looking at reanalysis gridded temperatures and anomalies up to the 26th reveal what I think was really going on. The core of the heat was across the north of Algeria and Tunisia, occasionally some of that very hot air escaped transferring northwards from Africa to affect parts of Sardinia, Sicily, southern Italy, western Greece and the Balkans, and because SSTSSTSea Surface Temperatures temperatures in the Mediterranean were at record levels during July, the sea didn’t cool the air at the surface as much as it could. The other thing is the media got a hold of this story and ran with it, this was easy to do, because they already had stories about heatwaves in the southern states of America and China, and as the month went on wildfires broke out, and it was also announced that July was very likely to be the record hottest month – a perfect combination for catastrophising the whole thing🥵. For the record heatwaves don’t cause wildfires people do.
It seems to me that even allowing for the rise in temperature due to global warming, there’s been an additional surge in temperatures across Iberia and northwest Africa in recent years. That’s particularly noticeable in summer, but can also be seen in the rest of the year too. The latest plume event is ongoing at the moment (27 April 2023), but has had a limited northward extent so far. I decided to look back at the last 40 years of daily maximum temperatures at Cordoba to see what I could find by plotting a scatter graph and adding a trend line.
As you can see I’m using the 1981-2010 LTALTALong Term Average. This is usually defined as a 30 year period by the WMO., which is courtesy of Wikipedia, and not the latest, but the linear trend at Cordoba does show a warming trend of well over a degree a decade. I can’t say if these results are just local to Cordoba, or if they’re occurring more widely across the rest of Iberia and Northwest Africa, but it does go a long way to explain the media hype about the present heatwave. I’m sure some more detailed research would find that there’s been an increase in Spanish plumes events in all seasons of the year, and that their effects aren’t just limited to the Iberian peninsula.
