grape harvest a la nina

Posted by Robin Ransom on 1 May 2011 | 0 Comments

Global weather has just come through a fairly intense La Nina episode.

La Nina is one extreme of the phenomenon called The Southern Oscillation, the other extreme being El Nino. Reciprocal changes in surface air pressure between the Eastern Pacific and the Western Pacific, measured by weather data from Tahiti and Darwin respectively, produce this phenomenon. In the El Nino phase the effect on summer weather in New Zealand is that it is generally dry and often droughty, with consistent south-westerly air flow, plenty of cloud cover in the north and not particularly hot.

La Nina produces much warmer weather than usual in the summer with plenty of sunshine, but it can also be considerably wetter, with the risk of more tropical cyclones descending on us from the vicinity of the Coral Sea.

For grape growers La Nina can be challenging. All of New Zealand’s wine regions experienced this summer’s version, which gave us consistently warm and sunny weather throughout the summer, excellent for bringing grapes to maturity, but also a good deal of rain. Much of the rain came in two events on consecutive weekends in late January – both resulting from ex-tropical cyclones. Many readers will recall vividly the flooding and damage they caused. These storms had the effect of saturating our soils, and a few subsequent “top-up” rain events spread through the remainder of the summer and early autumn ensured that the soil never dried out as it does in a “normal” summer.

The effects on the Matakana grape harvest have been mixed. Moist conditions encouraged more mildews and bunch rots than usual, which meant more work in the vineyard to control disease and remove rot affected fruit. This resulted in smaller crops, but wetter soils produced large and very juicy grapes. The abundance of warmth and sun meant the fruit achieved very good levels of ripeness, but the juiciness could possibly mean slightly less intense wines. The jury is still out on that one.

The relatively trying conditions of the vintage inevitably produced a measure of disappointment amongst winegrowers, especially compared with 2010 which was exceptional in every way. But now that the vintage is over and the glorious aromas of fermenting wine are starting to subside in the winery, winemakers are in a better position to evaluate the results of 2011. We are certainly very satisfied at this point with what we have in tank and barrel, both in quality and quantity.

Robin Ransom

(published in Mahurangi Matters, May 2011)