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Water Stress Monitored

CONTENTS
1. The study
2. The decision-making
KEY POINTS

The drought in the vineyards has become a recurring topic for several years. Winegrowers have to adapt to difficult climatic conditions, extreme temperatures, and a severe water deficit. These climatic events have major consequences on yields and harvest quality.

Is the Pessac-Léognan appellation threatened?

The increasing temperature and the change in rainfall pattern, expected in the next decades, should bring changes in winemaking practices. Modelling enables to better assess the impact of climate change on wine production. A study conducted by ITK on the effect of climate change on water deficit of representative vineyards located in Pessac-Léognan during a 120 year period (1980-2100).

The study’s investigated the evolution of the Cool Night Index the month before vine-harvest. This index is related to the aromatic potential of wine and may evolve in the next decades under the combined effect of global warming and earliest harvest date. The retrospective part of the study (1955-2014) made clear that the management mode prescribed by the specifications of Pessac-Léognan appellation well matched for wine production without irrigation under the climate conditions of 1980-2000.

Production objectives should require doubling water input until 2100.

Climate shift then led to an increasing water deficit and highlight the limits of traditional management. Predictions show that the production objectives should require doubling water input until 2100, whatever the management mode of the inter-row. The effect of cover crop on water deficit is negligible compared to the expected effect of climate change until 2100. It does not focus on the other beneficial aspects of cover crop, but underlines the need to develop new solutions that should counter the evolution of water deficit.

The vine water needs on daily basis has been used to better control water consumption, whilst complying with the specifications obligations. Earliest grape harvest dates (from 2 weeks to 1 month) are expected in parallel. This shift combined with the increasing temperature should significantly alter the Cool Night Index and ultimately compromises quality objectives. This might be a problem for wine quality.

Côtes de Provence use a decision-making tool

The local weather data and field observations used to prepare the application for exemption can demonstrate water stress. The Côtes de Provence wine institute has wished to equip itself with an efficient and precise decision-making tool in order to refine the diagnosis of the situation of the vineyard, hence operate at the most relevant time. Knowledge of the water status of the vine is essential for the management of the vineyard both quantitatively (yield) and qualitatively (organoleptic profile).

Ten plots were simulated in order to have the best representation of the Côtes de Provence’ terroirs. Coupled with field monitoring and foliar water potential measurements, the water balances showed an accelerated fall in the basic foliar water potential (below -0.2 bar), as well as in the water reserve usable by the vine in the soils (below 30%) at the end of June.

The Côtes de Provence wine institute’s advised the winegrowers to control irrigation during the growth of the bay to reach the profile of rosé wine desired by the French appellation.

KEY POINTS
  • Modelling to assess the impact of climate change on wine production
  • Production objectives should require doubling water input until 2100
  • This might be a problem for wine quality
  • A tool in order to refine the diagnosis of the situation of the vineyard
  • Control irrigation during the growth of the bay to reach the profile of wine.

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