Saturday, March 19, 2011

Water stress.

The Napa Valley has had its fair share of rain this winter (except for January) and, like most of Northern California, has accumulated more rain so far this month alone than on average for a typical March. As a consequence, there are many vineyards on the valley floor that are partially under water (as illustrated in the above photo of the Swanson Vineyard in Oakville). Thankfully, the vines, whilst in full dormancy are not adversely effected by being water-logged. Conversely, water-logging during the growing season, as a result of summer rains that saturate the soil, can create an anaerobic environment in which the roots cannot survive due to a lack of oxygen. As of Wednesday, State agencies began releasing water from California's reservoirs to make way for a series of storms (the meteorologists word, not mine) expected to last into next week.
Climate is usually listed, along with variety and soil type, as one of the most essential factors controlling the composition of grapes. Whilst sunlight might be the single most dominating climatic factor affecting the makeup of the grape, there is one other essential ingredient - water. The soil underneath a grapevine is a veritable reservoir of H2O, the volume of which is classified as; available, unavailable, gravitational, and superfluous. I don't know about the grapevines, but I would definitely categorise the current amount of water in Vinoland as my well-being!
The dry summers in California are a boon to the wine industry (if not in the least for the fact that arid climatic conditions mean that the vines are less likely to suffer injury from harmful pests and organisms). However, under extreme drought conditions a lack of rainfall may cause the failure of a crop to ripen. Vines, like any other plant, need sufficient water availability for photosynthesis, (photosynthesis begets sugar, which in turn begets alcohol). Soil moisture content is very important.
Napa Cabernet sauvignons, from 2007, are said to be some of the best in recent vintages. Preceded by two relatively dry winters (05/06 and 06/07) the berries at harvest time were notably smaller, meaning the skin to pulp ratio was up, a condition that boded well for a flavourful vintage. I have heard several people in the industry comment that if a winemaker had made a bad Cabernet sauvignon in 2007 then he/she really had no business making wine at all. That is perhaps a tad harsh, but reduced soil moisture content is generally accredited with the success of that particular vintage.
It is possible then that one could be forgiven for assuming that 2011 is already destined to be a difficult vintage. Truth is, studies have shown that winter rainfall in California makes little, or no, difference to the final grape crop as a result of an elevated soil moisture content at the time the growing season gets underway. So, when somebody brings up moisture stress in grapevines they are usually referring to a deficit water situation, not the other way around.
Maybe the only thing water-stressed around here is me!


Cesar Valverde said...

Crackingly informative stuff. Cheers.

Just out of interest- what weather does affect the vines when dormant? Sprintime frost presumeably, but others? Also- what are the ideals you'd be looking for now? (ignoring what may or may not happen in the summer).

Vinogirl said...

Cesar, ideally we'd be having less rain right now, so that I could actually get out and finish pruning!!!
Nothing really affects the vines in their dormant season here on the west coast. In the east however, severe frosts can kill the above ground portion of the vine and extreme measures have to be taken in the vineyards.
Now that budbreak is underway in Vinoland I am praying for nil frosts that would kill the primary (fruitful) buds.
When the new shoots are at 3, 8 and 12 inches I will be praying for no rain, so that sulphur applications to protect against PM are not washed off the young, green tissue.
Dry weather and no that too much to ask?

Thomas said...

In answer to your final question, Vinogirl: yes, at least as farming goes...

I'd also say that without sun, photosynthesis won't happen. I think sun is more important than water in that regard. Here, because of the oblong shape of the lakes, vineyards generally face east or west and that is one more reason for the struggle to get sugar up.

Thud said...

I remember a certain someone saying that they liked the rain...clue...not me!

Thomas said...


Yeah but you have to give some slack to us crazy-minded viticultural the very least you have to expect dysfunctional thinking from someone odd enough to believe he or she can negotiate with mamanature!

Vinogirl said...

Thomas: Just thought I'd try.
On photosynthesis - without the electrons that are removed from water particles, to kick-start the whole process, there would be no light reactions and certainly no Calvin cycle. Can we just agree that both water and sunlight are essential?
Mamanature, as you call her, continues to thwart my Sunday pruning plans!

Thud: I still think rain is fun for a little while, but this rainy season is just ridiculous!

Do Bianchi said...

great post, as always... :)

Thomas said...

Yes, we can agree on that, Vinogirl.

As for mamanature: she is the chief thwarter.

Cesar Valverde said...

Ah you want to move the sunny, south-facing slopes of the Wirral... the UK is set to have it's driest March ever by quite some way according to the BBC.

Thud said...

Cesar... tis indeed sunny on the wirral today and my doughty builders are delirious with joy...I may even let them see it for a while.

Ron Combo said...

I can honestly say that I have never been water-stressed. Alcohol-stressed yes and often, thank the Lord. And you know Launceston VG. Well, how about that. Small world indeed. Long live your vines, whatever the state of the water table.

Vinogirl said...

2B: Thank you :)

Thomas: Oh, the old girl is not so bad.
Thwart away mama, I'm up for the challenge.

Cesar: Yes, spoke with my mother today and she said the weather is lovely. I suppose you sent it all my way!

Ron: As kids, Thud and I spent all our summers in Devon or Cornwall, or often both.
My vines, like me, will survive!

NHwineman said...

Vinogirl, you have reminded me of a film (chick flick), but I'm not sure whether you are reminding me of Glenn Close or Christopher Walken;-)