Are the wines from Bordeaux region threatened? Vineyard adaptation to climate change is one of the biggest challenges for viticulture. Contrary to the Mediterranean region, past impacts were negligible or even beneficial for the production of quality wine. Nevertheless, several studies suggest that the situation will get worse and can become problematic to keep the quality and yield objectives. Logically the increasing temperature and the change in rainfall pattern, expected in the next decades, should bring changes in wine-making practices. Modelling enables to better assess the impact of climate change on wine production. As an example, the itk Company carries out a study on the effect of climate change on water deficit of representative vineyards located in Pessac during a 120 year period (1980-2100).
This study is based on simulations carried out with itkVigne software developed within a collaborative project involving INRA, CIRAD, IRSTEA, Languedoc wine-growers’ cooperatives, the regional department of agriculture (chambre d’agriculture) and the climate association of Hérault. This software defines the daily optimal irrigation need through the modeling of vine water deficit. It also enables the simulation of the effect of cover crop on soil water dynamic. In this region, cover crop is widespread and represents up to 80% of wine-growing area. The effect cover crop on water deficit until 2100 was investigated according to 3 climatic scenarios defined by IPCC. Otherwise, we investigate the evolution of the cool night index (CNI) the month preceding 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. This evolution of CNI might be problematic to maintain wine typicality. The retrospective part of the study (1955-2014) make clear that the management mode prescribed by the specifications of “Pessac-Léognan” appellations well matched for wine production without irrigation under the climate conditions of 1980-2000. However, climate shift then led to an increasing water deficit (Figure.1) and highlight the limits of traditional management. The predictions show that production objectives should require doubling water input until 2100 (i.e. scenario A2 and A1B) whatever the management mode of the inter-row (Figure 2). The effect of cover crop on water deficit is negligible compared to the expected effect of climate change until 2100. It does not question the other beneficial aspects of cover crop, but underlines the need to develop new solutions that should counter the evolution of water deficit. In this context, itkVigne proposes to estimate vine water needs at daily time step in order to better control water consumption whilst complying with the specifications obligations. Otherwise, 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 CNI and ultimately compromises quality objectives. This might be problematic for wine quality and difficult to counter except by using late varieties.
These results already show that itkVigne is a relevant tool to quantify the effect of climate change on potential wine quality and its interaction with vineyard’s management. In this domain, mechanistic models have decisive advantages compared to physical measurements as they deliver a continuous follow up of base water potential. It can be used for longer-term impact studies.
Marek DUPUTEL & Philippe STOOP
Predict and Decide