From hurricanes and heatwaves to droughts and deluges, weather events of biblical proportions are striking with startling regularity. It's enough to drive one to drink. However, with a global water crisis predicted within the next 20 years, there may not be enough water for humans to drink, let alone irrigate vines.

It is estimated that a vine needs between 250 and 1,000 milliliters of water during the growing season, which nature sometimes fails to provide. No problem, say many New World wine producers; let's turn the irrigation system on. But they should think twice, says soil expert, Dr. Emmanuel Bourguignon – and not simply for environmental reasons. He claims that irrigation dilutes terroir.

The reasons, Bourguignon explains, are twofold. Firstly, irrigation allows the vine to be lazy; the roots stay in the top 40 centimeters of soil and don't seek out the goodness in the sub-soils and sub-solum.

“Permanent irrigation leads to a shallow root system. You get a really big mat of fine roots in the first 40 to 50 centimeters of soil,” he says. “The most fertile horizon in the soil is in that first 40 centimeters because that is where you have the organic matter. If your roots stay in that horizon you will end up with some slight vigor problems.”

This increased vigor creates a large canopy, which is particularly problematic in sunny climates. 

“You end up getting massive photosynthesis – you just end up with a high level of sugar and your alcohol potential is high," says Bourguignon. "So you dilute the terroir, but you tend to increase the varietal character. You can have a good canopy and make a good varietal wine.”

That's fine if you are making an entry-level fruity wine, but you can forget about minerality and sense of place.

“This is a world where people want to be unique and stand out. It's going to be much harder to achieve that [with irrigation]," notes Bourguignon.

And his opinion is widely respected – along with those of his soil-loving parents, Claude and Lydia Bourguignon. The family has worked with the who’s who of the wine world, including Domaine de la Romanée-Conti and Domaine Dujac in Burgundy, Domaine Huet in the Loire, Vega Sicilia in Spain and Harlan Estate in the United States.

But irrigation isn’t all bad. In fact, without irrigation, many wine regions wouldn’t be viable: there would be be no Mendoza malbec or Leyda sauvignon blanc, and that would leave consumers crying into an empty glass. Admittedly, some less-scrupulous wine producers use irrigation to increase their yields, but without irrigation many good producers would see their vines struggle. For example, at Huia Vineyard on the free-draining gravel soils of Marlborough, chardonnay blocks are irrigated up to twice a day at the height of summer to prevent excess stress.

Indeed, a lack of water can cause many issues throughout the season. The vine needs water during flowering and fruit set in the early summer. Later in the season, the stomata – the pores on the leaf – may close, in order to reduce evapotranspiration during times of water stress. But because the vine needs to obtain CO2 through the stomata this can reduce photosynthetic ability. In the worst cases, leaves can drop off the vine, preventing the vine from ripening its fruit.

However, Bourguignon believes that vines can manage quite nicely without water.

“There are vineyards in Turkey and Lebanon that get less than 400mm of rain a year and are thriving without irrigation,” he points out. Vines will do as little as possible to reach a water source. Make it tough for them and they will work harder. “The vine will naturally shift resources. If it doesn't get a lot of water it will use more energy on root growth to get to water,” Bourguignon explains.

The soil expert also reports that vines have got the ability to “go round obstacles or find cracks” in rocks in the ground; as a result, preparing the ground before planting by ripping the soil is a waste of time.

"Many people rip up the soil because they think they vine won’t be able to get down there, but I don’t think we give enough credit to the vine as an organism," says Bourguignon. "We need to have faith in the plant – it is capable of wonderful things.”  

There's also the environmental question to consider. Globally, water is becoming increasingly scarce, yet while many wine producers are looking at ways to reduce their water usage in the winery, they continue to irrigate. New World wine-producing regions from Chile and California to New Zealand tout their sustainability credentials, but large swathes of the industry cannot survive without irrigation.

"Water is becoming a scarce and expensive resource, plus there’s the energy needed to pump the water ... you have to question the sustainability of that kind of irrigation,” observes Bourguignon.

Certainly, Bourguigon isn’t alone in his opposition to irrigation. It is forbidden in many of Europe’s classical wine-growing regions, although it was widely permitted in 2003 due to exceptionally hot and dry conditions. With the extreme weather events that the world has experienced in the past decade, it would not be surprising if the 2003 exception becomes a norm in the future. 

Whatever your notion of terroir, wine cannot be made without humans tending the vines and nurturing the wines. If irrigation is the devil incarnate, obscuring terroir, it could be argued that blending wines or barrel maturation have the same effect. It all depends on your interpretation of the t-word, but that floodgate shall remain firmly closed!