January 8th, 2024

Hi All,

Last Tuesday I decided to get out for a cycle to work off some Christmas-acquired lard just as the end of Storm Henk was doing the rounds. I have never in the 50 years plus that I have been out and about in The Welland Valley seen not only the volume of water pouring out of the land, but the strength and force of this water. After negotiating numerous field floods, I made it to the ford at Medbourne on my trusty Merida mountain bike, which runs dry most of the year (the brook goes under the road) and was amazed at the height of the water and its ferocity, quite amazing. It took all of my nous to work a way back home in the driving rain through the shallowest floods, great fun.

By now of course, we all know that 2023 checked out with a very wet December and January 2024 has already brought some areas their monthly rainfall. Looking back at the stats though, whilst it does pick out 2023 as a 'wetter year', it isn't the wettest, nor is autumn / winter 2023, the wettest, but the impact of the rain at the end of last year and start of this one seems unprecedented.

Why ?

One explanation is of course the fact that the soil was saturated leading up to the end of December. The number of wet days since October (and in 2023 full stop) has been significant with very few opportunities for the soil to dry down in between the next storm system. You can see this in this graph of soil moisture deficit / surplus status from a golf course near Sevenoaks, Kent. You can see how September is typically a neutral month when it comes to rainfall vs. E.T, the two tend to balance each other out, but once we start get into October, the soil moisture surplus begins to grow. It normally does at this time of year but the extent of the surplus and the high volume / short-term increments mark it out as exceptional.

Here are the stats that lie behind the above graph ;

Secondly, we have had a very active jet stream with a low-lying southerly position which has allowed storm system after storm system to push into and across the U.K & Ireland. Some of those storm systems have been very slow-moving so the rainfall amounts associated with them have been significant. Another point to note that I have discussed frequently in this blog is the increased frequency of BOB's and more southerly-orientated storm systems during 2023. This will be seen in the rainfall totals I post next week where you will see much higher significant rainfall across the south and south east of the U.K and Ireland. I don't understand why this is a feature of our climate other than as a consequence of the jet stream position. Note - a more southerly-orientated latitude position for the jet stream allows low pressure systems from the Bay of Biscay and mid-Atlantic to impact the U.K & Ireland further south.

Last, but by no means least, is my oft-repeated point, that it is rain rate (measured in mm per hour) that causes the most impact in terms of flooding events, overwhelming drainage systems, ditches, rivers and flood schemes.

If you look at December 2023 in isolation, we can see how the points above all contributed to the end of an 'Annus horribilis' from a rainfall perspective.

From the stats obtained via a Davis Vantage Pro 6820 situated at a golf club close to Bristol, we can see why December 2023 was such a difficult month.

I count 7 dry days out of 31. A total rainfall of 214.6mm for the month, that's just over 8 1/2" in old money and just look at the last 5 days of the month.

70mm of rain but on just about each day the rain rate exceeded the violent rating (> 50mm per hour), with a whopping 182mm per hour rain rate on the 27th. So for five days in a row, the rain rate hammered down on the land overwhelming (in some cases) all the good work done to increase infiltration. Just to cap it off, the first 4 days of January brought another 67mm with again a violent rain rate (87.2 mm per hour) recorded on the 3rd courtesy of Storm Henk.

So in the last 5 days of December and first 4 days, this golf course received just under 140mm of rainfall, with 6 violent rain rate events thrown in. That's why surfaces are totally saturated as we come into this week and a very welcome dry spell courtesy of an Omega Blocking Event shown in the graphic below from netweather.tv. You can see very clearly from this image why the blocking event shown has this name from the Greek letter Omega - Ω

General Weather Situation - w/c 08-01-24

So this week promises a dry and settled week with (shock horror) below-average day time temperatures and long overdue it is too !

Now the arrival of this blocking event means that not only will low pressure systems be blocked from pushing across the U.K & Ireland (hence the name) but its formation signifies that the jet stream has temporarily lost its strength and is now less likely to introduce Atlantic low pressure systems into our weather picture.

What it does also do though is open up the scenario of colder air from the north and east pushing in to influence our weather dynamic, particularly from mid-January onwards I'd say. So that means an increased likelihood of snow I would say and a decreased likelihood of prolonged wet weather, such as the like we have recently endured.

So this week looks pretty dry and cold and dependent on cloud cover, frosty overnight. Temperatures looks to sit between 4-6°C day time and close to or below freezing at night, wholly dependent on cloud cover. We look to stay pretty dry all week with just some rain arriving into the north west of Scotland over the weekend that may push some wintry showers down across the north of England on Sunday.

I say pretty dry because a north and north easterly wind direction as we will have this week always allows the development of showers to push in from The Wash, Humber and Thames estuaries on and off. As I type this I can see some showers over southern Kent and I'm guessing they may be falling as sleet and snow. On the whole dry though and that is to be broadly welcomed. Winds will be northerly with a touch of easterly early in the week swinging round to north westerly by the weekend to give slightly milder temperatures and that rain to the north west of Scotland.

Weather Outlook - w/c 15-01-24

We know of course that as welcome as it is, one dry week won't repair the harm of an extremely wet December across the U.K & Ireland, but it is a start. All eyes then will be looking at next week to see if this blocking event stays in situ. Currently the 7-day onwards weather synopsis is a messy one with no clear pattern discernible. This means to me it is likely to change in between this blog and the next. It looks to be staying pretty cold though with north winds dominating the start of next week and the continuing potential for wintry showers across North Sea coasts and the eastern side of the country.

Thereafter unfortunately we have the potential of a southerly-biased low pressure system to influence the southern half of the U.K and Ireland over Tuesday / Wednesday before departing. At the same time we could see some significant snowfall further north as a low pressure system pushes moisture down into the existing cold air sitting over Scotland and the north of the country. So a potentially wet interlude Tue / Wed next week before hopefully we go drier again as high pressure builds across the U.K & Ireland. I am hesitant about the above because when we have a blocking event breaking down I find the accuracy of the 7-14-day forecast to be low. What I do see is plenty of cold air to the north and east of us which in my mind means a colder January than we have been used to of late but hopefully not as wet as it began :)

The El Niño Effect

Before I head onto the agronomics part of this blog, I think it is worth briefly mentioning this factor when we look at how this year may develop as a weather year.

2024 will be the 2nd year of an El Niño effect and is often the year when we see the greatest effect on the world's weather. El Niño is a warming of the sea temperature in the central / eastern Pacific Ocean and whilst this may seem a long way off from us, its effect is often felt across the world. You can read about El Niño and its opposite relation (quite literally) La Niña on The Met Office's site here.

Now as I have said before, the fact that the U.K & Ireland sits on the path of the Polar Jet Stream and are both islands can often prevent us from experiencing the full wrath of summer heatwaves elsewhere. Just look at summer 2023 as proof of this. Europe experienced record summer temperatures, widespread drought and was ravaged by wild fires, whilst we experienced a very wet summer and numerous storm systems.

2024 may well be different with the enhanced El Niño warming effect on the world's climate. So we should be prepared for a summer peak pattern / blocking event that may allow heat to extend northwards from Africa and southern Europe into the U.K & Ireland. If it does, it wouldn't surprise me for the U.K's hottest temperature record to be broken again, 42°C plus anyone ?

Agronomic Notes

So I will start this agronomic section of this week's blog by taking a cursory look back at December and of course year end. How did 2023 finish from a GDD perspective ?

December 2023 - GDD (6°C base) - The Oxfordshire, Thame, U.K

So as we can see that December 2023 came in with a total monthly GDD of 72.3, that is the 2nd highest total we have seen since 2005 and double what we 'usually' experience for December as a month. Hardly surprising with a strong and mild westerly / south westerly airstream. The record set in December 2015 was recorded for precisely the same reason.

That very high December figure pushed 2023 right up there from a yearly total GDD, coming in at 2083.2. So that means that since 2017, 5 out of the last 7 years have been > 2,000 total GDD when previously we only had recorded 1 year since 2005 that surpassed a total GDD figure of 2000 (2006).

If you break it down into seasons, it is even more interesting (if you are sad like me !)

As I have stated before, it is difficult to pick out seasonal trends, when we look at GDD totals and that's because I think of our jet stream and the vagaries of blocking events. That said, Sept - Dec 2023 comes in as the second highest total on record and as part of a steadily increasing trend since 2019. I wonder where we will sit this time next year ?

Moving water away........

Over Christmas I have seen a lot of discussion concerning aeration, penetrants and the like with a view to moving water away and achieving a drier rootzone.

It is a complicated subject with no single magic silver bullet. It comes down to joining the dots of course between moving water through / from the surface down into the amended rootzone below and then ultimately to your deeper drainage system 'dependent on your rootzone make up'.

The phrase, 'dependent on your rootzone make up' is the bottom line in my mind.

If you have poor drainage and / or a deeper rootzone profile that is non-conducive to water movement, then any work done above that will only serve to move water faster from the surface down into this layer whereupon it will sit and back up. Effectively by trying to achieve a drier surface, you will actually make your greens wetter as water moves down through the surface fibre rather than shedding off during high rainfall events.

In other words, it's better to leave well be and then focus on achieving deeper water infiltration when ground conditions are more conducive to do so. The same is true if your soil type has a significant clay content. Again aeration, though well meaning, will just achieve a smeared channel which will rapidly fill with water and just sit there. Better to leave Mother Nature and its hopeful pattern of freeze / thaw to effectively create fissures in the rootzone by the natural expansion and contraction of water.

Using a penetrant in any of the above cases will not achieve anything as the main issue is a physical barrier to water movement. So know your rootzone characteristics, take note of wetter areas during the period of weather and try to understand why. Is it a rootzone problem, surface organic matter accumulation, a collar dam effect backing up water onto a green or just a lack of effective drainage ?

Chances are it will be a combination of the above.

All the best for the coming week, wrap up well and enjoy some cold but drying weather :)

Mark Hunt