Search

Now for the Science Bit

It should be a quiet time at Little B now. Summer is over, the final cover crop before next year’s planting is in, but I was there for several hours this week fiddling around with electrical bits and bobs connected with my Davis Vantage-Vue weather station. This gadget has the perfect ingredients to be a complete and utter drain on my time. For a start there are multiple potential points of failure to keep me occupied: the weather sensors themselves, the router that beams real time data to my smartphone, or (this week) the solar panels that charge the battery that keeps all the components going. But there is also the fact that the weather is a hobby of mine, and hobbies can be vortices of time and money.


Being a weather nerd is a bit like being an English wine buff. You end up spending too much time evangelising people who frankly aren’t interested. But there’s also the hallelujah moment when you find fellow enthusiasts. Judging from the number of vineyards publishing their live weather stats online – just among Davis weather station users I can view data from, as a sample, Simpsons, Oastbrook, Exton Park, The Mount, and Fox and Fox – I suspect a few vineyard managers are similarly partial.


But weather buffery and English wine are a natural match because the weather is such a dominant player in our ultra-marginal terroir. At its simplest, “terroir” is a fancy name for those physical geography factors most important for grape growing: macro and micro climate, aspect and slope, drainage, soil type and profile. The French word may sound a bit soily, and anyone familiar with French approaches to geography will know there is a big emphasis there on geology as a shaper of landscapes, but here in cold cloudy Britain the microclimate is by far the most important influence. Essentially because British weather is crap. The secret to great English viticulture is to find a spot that is just un-crap enough to bring grapes to a sort of ripeness by mid-October.


And now we have a full year of data from our little weather station and are ready to share it with the world. What follows is a run-down of what we now know about the climate at Little Bursted and what this might mean for the future. This may or may not interest you. I’m writing it because it interests me, and in the vain SETI-like hope that one or two readers may feel it worth a read.


Little Bursted’s climate


So here are the charts from our first 12 months.



What do they tell us? First, that this was a very odd year. It's not often November is the third driest month of the year, or May one of the wettest. Still rarer that April is colder than February yet one of the driest and sunniest on record. But putting aside the oddities of 2021, these charts tell us a bit about Little Bursted too.


Climate for a vine grower is the product of 3 things: the large scale, regional climate (where in the world is the vineyard); the medium scale "mesoclimate" (is it near the coast, up in the hills, in a rain shadow?); and the microclimate of the site itself (what direction does it face, how high is it, is it frost prone and so on).


Those charts show you the sum of all of these factors.


The large scale or macroclimate


This is the global context in which the vineyard is placed. In our case, that’s in a cloudy and windy corner of the North Atlantic at or around 50 degrees North. Our climate is maritime temperate, but then so are Bordeaux, the Willamette Valley or Rias Baixas. The difference is that ours is more rubbish. I probably don’t need to go into more detail other than to remind you that our prevailing airmass is maritime tropical, our prevailing wind is Southwesterly in winter and Westerly or WNW in winter (but at Little Bursted there are some interesting local features I’ll describe later), summers are cool and winters are mild, and rainfall is regular throughout the year peaking in Autumn with a minimum in Spring.


In fact I’m being treated to a masterclass in the maritime English climate through the window today. If you are lucky enough to live somewhere with crisp sunny winters, then have a read of the first page of Bleak House, these days minus the smoke and soot, to get my drift.


But the climate is changing, as we know. Most trends are beneficial to English viticulture: warmer summers, a longer growing season, potentially lower summer rainfall, and more sunshine. The following Met Office maps show where we are now, and what we might expect in the coming decades. All the projections, regardless of mitigations implemented in the next few years, show more warming for the next couple of decades.



The regional or meso-climate


This is where things become more interesting. We are in East Kent, in the middle of the North Downs. The mesoclimate is a bit of an odd mixture of factors that are alternately helpful and problematic for our location.


We are a long way East. Whilst surrounded on 3 sides by sea and estuary we are also that much closer to the continent than areas to our West. This makes itself known during Central European heatwaves where East Kent is often the last place to see the heat dissipate, or even the only region to import very hot air. It’s also apparent in Easterlies. The short straits mean the airmass is largely unmodified and some of the coldest winter temperatures can be recorded in this part of Kent. In 2018 Brogdale near Faversham recorded the national coldest temperature during the late winter “Beast”, and until 2019 it held the record for the highest ever temperature, set in 2003.


Like Essex, we benefit from the fact that large scale frontal rainfall dissipates as you go East, but the surrounding sea inhibits summer convection. Low lying areas of East Kent near the Estuary and along the South coast are some of the driest in the country in summer and set to get drier still as a result of climate change.


But confounding all this are the North Downs. In the relief map below (https://en-gb.topographic-map.com/maps/sm4c/Kent/) we are in one of the little wormy yellow valleys pointing up towards a kink in the A2 South East of Canterbury.


They’re not that high, topping out at around 200m, but

that is enough to make the area much wetter on average than the lowlands to the North and South. Our rain gauge bears that out. It doesn’t rain particularly more often than elsewhere in Kent, but when it does the totals are higher. In the last 12 months we have measured over 1,000mm of rainfall. Manston, in Thanet, has reported 614mm for the same period (https://www.metoffice.gov.uk/pub/data/weather/uk/climate/stationdata/manstondata.txt).


Rain is not a huge problem for vines – take Maconnais-Beaujolas for example, where it averages over 100m in May and June – but it’s a nuisance because it can mess with flowering and in wet summers like 2021 can encourage downy mildew. The vineyards of East Anglia and the low Weald have it a bit easier.


The height of the downs also cools the average temperature a little. We are at 80-100m above sea level, the same as a few neighbouring vineyards. This makes us around 0.5C cooler across the growing season than an equivalent sea-level site.


The microclimate


The Pett Bottom valley is an odd feature with its own unusual weather features. We’re in a raised dry valley and this does a few things to the microclimate.


First, frost. The shape of the valley and our location near the bottom makes it a perfect site for radiation frost on calm nights. So perfect in fact that any vineyard textbook would tell you to avoid it like the plague. More on our frost protection efforts in a future blog. This is borne out by the station stats. I closely monitor the weather station at nearby Railway hill in Simpson’s wine estate because it’s at the same altitude more or less, with the same Easterly aspect. On still clear nights we can be up to 5C colder than Railway Hill in the early evening (things tend to even out a little later in the night). That’s the difference between zero damage and crop wipeout.


This April, which admittedly was one of the frostiest on record in the South, we had 20 air frosts. 20 air frosts, if your buds have already burst, would be ruinous to anyone relying on bougies. Luckily it was so cold in March that nothing was growing yet, so Graham up the valley escaped with no frost damage at all.


But then the other type of frost hazard – advection frost – seems to affect us less than many other areas. The sheltered valley location means that in screaming Northerlies or Easterlies we are often a degree or two warmer than other Kent vineyards and much warmer than places West of London.


The shelter means we get little wind and what does blow is almost always from the SSW or NNE, in line with the valley orientation. The wind rose pattern is remarkably consistent. With trees above and around us the vines will be well sheltered and should be able to retain the heat that builds up on warm summer days.


So when there is wind around we are relatively warm. When it’s still we are warm in the daytime, cold at night. This shows up in a really pronounced mesa-like daily temperature profile. The slope faces ESE so it heats up very quickly in the morning, then often plateaus during the day before cooling down almost as rapidly as soon as the sun goes down. Look at the graph below.


What does that all mean for grape growing? Well, in a hot climate our large diurnal range would be a blessing. Allowing for phenolic ripening without overaccumulation of sugar. In a marginal climate like Britain though? Probably a slightly slower ripening compared to exposed South facing slopes, but plenty of growing degree days to bring grapes to reasonable ripeness even in poor summers. This year for example we recorded 850 across the season, though that number is suppressed a bit by a few short cold nights.


But, Little Bursted is not the Crouch Valley, Isle of Sheppey or Medway valley. We are certainly not super dry, and we clearly get some enhanced orographic rainfall in winter. On top of that more convective activity (clouds and rain) in summer as well as pretty good shelter from the hills around us make us look more inland than the map suggests.


Our rainfall is higher than at low level sites, though not particularly more frequent. So it doesn’t happen that often but when it does, it rains a lot. We have no problems with surface water as the flinty soil is very quick to drain down the slope. But this year’s stats show why vineyards had lots of Downy Mildew in July and August. It was wet on and off for most of the summer in the far South East because a shallow trough sat over the near continent for much of the season.


Of course what I don’t know yet is how normal or unusual 2021 was compared with the norm in this part of the downs. I am confident the summer was abnormally humid: look at the relative humidity chart and compare the summer months with spring. Usually I would expect a low point in May and June and levels to jump only in September. I am relatively confident it was wetter than normal too, because the whole of Kent has been. And I am praying that 20 air frosts in April is not the norm, because if it is we might as well give up now.


But it’s our site, and so long as the power supply, internet and weather station hold up we have several more seasons of measurements to come before we get the most important measurement of all: the first harvest.




35 views0 comments

Recent Posts

See All