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  • Writer's pictureMark Hunt

July 26th - Diary of a heatwave

Updated: Jul 27, 2022

Hi All,

A little over a week ago we were experiencing our hottest day ever and I believe Scotland, Wales and England claimed that statistic.

For the record, the respective temperatures and locations were ;

England 40.3°C Coningsby, Lincolnshire (record)

Ireland 33.1°C Phoenix Park, Dublin

Scotland 34.8°C Charterhall, Borders (record)

Wales 37.1°C Hawarden, Flintshire (record)

The fact that these temperature records were broken not just by 0.1 or 0.2°C, but in our case by over 1.5°C, shows the severity of the heatwave we endured. The only positive factors for me were that it was well forecasted and true to type, it built progressively over a 4-5 day period as you can see from the temperature graph above. It was also mercifully short and the next day we were some 10-17°C lower in terms of maximum air temperature, dependent on your location. No matter what the "It's just summer" brigade 'nah sayers' claim, it was an extreme climatic event and you only have to look at the wildfires that started on that day and the ones that are still starting up as I type in our tinder-dry countryside to see what climate change really looks like. I'd imagine that even the sand is getting pretty hot to bury ones head in and ignore the reality of what we are facing.

I didn't see many turf horror stories on Social Media, wild fires aside, so I think we (as an industry rather than a country) managed this extreme well. What though if our water supplies had been limited because of water restrictions ? What then ?

A recent blog (above) was brought to my attention on LinkedIn (Thanks to Tony Hanson for that) and it documents the dire state of our rivers in terms of flow levels vs. normal. Interestingly rather than just being a south or south east England phenomenon, there are deficits all over the U.K, South Wales, The North East and Eastern Scotland. It is a great read but it does set some hares running so to speak. You can access it for a read here

Thankfully we have had 'some rain' although to quote 99% of greenkeepers, here in Market Harborough, "It just went round us !".....Mercifully as well we have had some cool northerly winds and man were they so so welcome, especially at night.

My attention turns then to where we are y.t.d. moisture-wise and some of the agronomic consequences of the above event. Has it highlighted at your facility deficiencies in your irrigation, water supply or just how you need to change to be better placed in the future ? Maybe you could drop me a line about your experiences @

Nature had a really hard time for sure, none of my birds came down for their daily suet sprinkles for 3 days, they just cowered in the shade and shut down, much like our grass. As soon as it was over though, they were on catch up !

Update - I had to break off writing this blog late morning as a young and not in great shape Hedgehog wandered into my garden. I managed to get some water down him / her but it was straight off to the Wildlife hospital because it didn't look like it was long for this world. I'd guess severely dehydrated with possibly an internal parasite issue.

Onto this week's weather....

General Weather Situation

A bit of a later start this week because I was out installing a couple of new Davis Vantage Pro's yesterday, so let's see where we are....Well you can see from the GFS output courtesy of that we have some cooler, northerly winds dictating our weather this week and that the extreme heat has shifted a long way south to Northern Africa. As it stands now, this shift in the jet stream's position further south will at least allow some Atlantic low pressure systems push through and bring rain to the U.K & Ireland, but it will be mostly for the west and north west / north. For us to get significant rainfall for the south of England, we would need a Bay of Biscay low pressure to form and currently there isn't one on the projections :(

So for this week we look to remain predominantly dry, some showers pushing across the south west and south of England but nothing of note and very few and far between. Plenty of cloud cover though to keep temperatures down but a change to a southerly wind will see temperatures creep up into the low twenties later this week across England and Wales. Scotland and Ireland will be 3-4°C down on this, just shading the twenties.

Later on Friday evening we see an Atlantic low push rain into Ireland, making ground break likely across Connacht first with a weak band of rain crossing Ireland into the early hours of Saturday. This rain will also turn up in heavier form across the north west and west of Scotland with some heavy rain likely for the west and central Scotland on Saturday. Wales, the south and north of England can only watch on in moisture-envy as Saturday looks to be a warm, settled day. Ireland sees more rain across the north and west and this will be heavier later on Saturday and into Sunday morning. This rain will cross The Irish Sea into the north west of England and North Wales and push across the north of England into Humberside / Lincolnshire. Currently very little is forecast to affect The Midlands or further south, though East Anglia and South Wales may pick up a drop. Later on Sunday that heavy rain clears Scotland and drops down into The North East bringing some welcome rain there. So some rain on the forecast but The Midlands south will miss most of it I'm afraid :(

Weather Outlook

So next week we start the month of August and as you can see from the animated GIF's and the projection we have low pressure in charge. This low pressure will continue the weekend's cooler, unsettled theme for Ireland, the north of England and Scotland through Monday with a chance of some showers slipping a bit further south. Later on Tuesday night, more rain arrives into the south west of Ireland and again pulls rain across the north and north west of the U.K, though there's a chance this may come a little further south, across Wales and into The Midlands. As is the case with an Atlantic low, we will have mainly south westerly winds until the end of the week when high pressure is projected to assert itself. Initially this will keep the picture cooler because it'll pull in northerly winds, but on the flipside, it'll reduce the likelihood of rain. Warmer and drier weather is then set to dominate (weekend after next) and there is the potential for heat to build under the peak in the jet stream so maybe (long way away caveat employed!) we could see another heatwave around the 11th-15th of August.

Agronomic Notes

Quite a stress event....with consequences....

So last week's temperatures would have constituted quite a stress event from a grass plant perspective as the maximum temperature was far above the optimum for cool season grass species. Obviously bentgrass copes better than Poa but when we are talking high 30's and low 40's, even species like Lolium perenne will feel it.

One of the great and pretty simple ways of understanding the potential magnitude of plant stress is to look at the Growth Potential (G.P) for the day in question. The formula for Growth Potential takes the minimum and maximum air temperature but also the optimum average temperature for cool season grass. It sets this at 20°C, but I actually use 18°C because it's more indicative of actual plant stress. The equation returns a value between 0 (no growth) and 1.0 (optimum growth) according to the daily minimum and maximum air temperature. When the maximum air temperature is very high and above optimum, the calculated G.P value actually decreases and this gives an good indicator of stress. The more above optimum the day and sometimes night temperatures are, the lower the calculated G.P.

So I've run some numbers for as many locations as I could get data from. There's only 1 Irish location as I had to hand write each daily maximum and minimum air temp figure from the MetEirann website and it becomes well....tedious.....

So here's how the daily G.P looked before, during and after the mini heatwave....

So you can hopefully see the significant dip in projected G.P during the heatwave with the locations in England and Wales worst affected. The lowest G.P figure recorded was 0.13 at Luton, which means potential growth would have been only 13% of optimum at that site, on that day. The Dublin and Dumbarton locations show only slight dips and that's because the night temperature (minimum temperature) at those locations was sufficiently cool enough to offset the effects of the high daytime temperatures.

It wasn't just hot last Monday and Tuesday, it was windy, particularly on the Tuesday and that ramped up the E.T. One of our stations recorded 7.62 mm for the day. That is a lot of water to lose and of course it further ramps up stress on the grass plant and the soil moisture deficit situation.

I don't have E.T data for all of the above locations, but here it is for July 2022 so far and remember, anything approaching 4mm E.T loss per day would in my mind constitute stress on Poa annua in particular.

Even the Scottish location showed high E.T's occasion in July and Sevenoaks, the highest moisture loss so far this month in total. The number of days during July so far, when the E.T was close to or exceeded 4.0 came out as 5 for Dumbarton, 11 for Luton, 12 for Guildford and 15 for Sevenoaks.

July 2022 will go down as a brutal month for E.T, lack of rainfall and high temperature.

So we had clear plant stress and on the back of two Anthracnose signals in May and June / July, I have already started to get reports of Anthracnose in greens. No surprise, entirely expected, and a tough one to battle if it's on your greens. You'll also note in the picture above, there's quite a lot of Poa annua seedheads which is another legacy of last week. Drought stress means less water uptake and therefore less nutrient uptake so Poa goes into survival mode and produces seedheads. They'll fade as we go through the next 7-10 days but I'd expect them to hang around again in August, if more heat does indeed arrive.

Soil Moisture Deficit Comparison - 2022 vs. 2020 vs. 2018 - Northampton

I am indebted to Rob Hay at Northampton County for access to some great soil moisture deficit data comparing 2022, 2020 and 2018. Rob is not only a great provider of support and data to me in general, but a thoroughly good egg and clever chappy to boot !

Rob has tracked rainfall (to filled capacity) vs. E.T for those 3 respective years using data from their Davis Vantage Pro weather station. It's interesting when you look at when the soil started going into a deficit situation and the severity of the deficit.

So for 2022 we are just ahead of 2020 in terms of soil moisture deficit though the figures are amazingly similar and just behind (10 mm or so) 2018.

You can see in 2018, the chart flattened out and began reversing (albeit only for 3 weeks before a dry September kicked in) on the 7th of August, 2018 as rain arrived and the same happened in 2020, on the 11th of August with a continued reversal through the whole month. I think by the end of July, we will be ahead of both 2018 and 2020 and certainly by the end of the 1st week of August.

This marks 2022 as a significant drought year and reiterates the blog article from the U.K Centre for Ecology & Hydrology that I began this blog with...

Fingers crossed for a southerly shift in the low pressures we are due in the next week or so :)

All the best.

Mark Hunt

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