Viticulture - raison d'être

 The hot, dry year has seriously affected my grape harvest...

2022 Grape Harvest

...indeed it is more akin to a raisin harvest!

Last year was much better...

Part of the 2021 Grape Harvest

The grapes are seeded so I always make grape juice by gently heating and mashing in a pan (briefly bringing to the boil to sterilise) before sieving through a muslin bag and bottling the juice. I enjoy the 'nectar' undiluted but Mary prefers a little water with her's. Both of us will have to forgo this pleasure this year.

Yields have dropped over the past 3 years. From about 4 litres in 2020, 2 litres in 2021 and zilch this year. One reason may be my viticulture skills (or lack of) but, I pondered, could there be a weather/climate aspect?

Grapevines thrive in a climate with 1300 - 1500 hours of sunshine during the growing season and around 690 mm rain with most of that in the winter and spring months. This summer has been sunny with May, June, July and August all having around 200 sunshine hours each. One thing it has lacked is rainfall. But how much?

I have been collecting local weather data for nearly 3 years now starting in November 2019. I harvest my grapes in October so I am interested in the rainfall from the end of one year's harvest to the start of the next year's harvest. Consequently, I have plotted monthly rainfalls from November (post-harvest) to the following September (pre-harvest) in the next three bargraphs. All plots have the same vertical axis for rainfall: 0 to 200 mm.

Rainfall was highest in the 2020 season (781.2 mm). It was 20% lower in 2021 (612.0 mm) and over 55% lower during the current 2022 season (358.8 mm) compared with the 2020 season.

Ideally, for grape horticulture, the bulk of the rain should fall in Winter and Spring with drier periods (and lots of sunshine & higher temperatures) in Summer and Autumn when the grapes are ripening. In all three years, 70% of the November-September rainfall fell within the 'Winter to Spring' period (Nov - May). We might infer, therefore, that it was the lack of rain in 2022 that resulted in the failure of this year's harvest rather than its monthly distribution. We need to be sceptical of this conclusion because 'correlation does not mean causation' and there may be other confounding factors (e.g. record daytime temperatures). For the time being, it is just a scientific hypothesis which is falsifiable using future data.

Drought has certain been mentioned as a cause for concern in the French and English winegrowing communities.


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