Abstract
Grapes for wine production are a highly climate sensitive crop and vineyard water budget is a decisive factor in quality formation. In order to conduct risk assessments for climate change effects in viticulture models are needed which can be applied to complete growing regions. We first modified an existing simplified geometric vineyard model of radiation interception and resulting water use to incorporate numerical Monte Carlo simulations and the physical aspects of radiation interactions between canopy and vineyard slope and azimuth. We then used four regional climate models to assess for possible effects on the water budget of selected vineyard sites up 2100. The model was developed to describe the partitioning of short-wave radiation between grapevine canopy and soil surface, respectively, green cover, necessary to calculate vineyard evapotranspiration. Soil water storage was allocated to two sub reservoirs. The model was adopted for steep slope vineyards based on coordinate transformation and validated against measurements of grapevine sap flow and soil water content determined down to 1.6 m depth at three different sites over 2 years. The results showed good agreement of modeled and observed soil water dynamics of vineyards with large variations in site specific soil water holding capacity (SWC) and viticultural management. Simulated sap flow was in overall good agreement with measured sap flow but site-specific responses of sap flow to potential evapotranspiration were observed. The analyses of climate change impacts on vineyard water budget demonstrated the importance of site-specific assessment due to natural variations in SWC. The improved model was capable of describing seasonal and site-specific dynamics in soil water content and could be used in an amended version to estimate changes in the water budget of entire grape growing areas due to evolving climatic changes.
Highlights
Grapevines are cultivated on 6 out of 7 continents, between latitudes 4◦ and 51◦ in the Northern Hemisphere (NH) and between 6◦ and 45◦ in the Southern Hemisphere (SH) across a large diversity of climates (Tonietto and Carbonneau, 2004)
Based on the allocation of radiation to the vine and soil components, Lebon et al (2003) formulated equations for potential vine transpiration T0,v and potential soil evaporation E0: T0,v where Rv, Rs, Rvy represent the radiation absorbed by the vines, the soil or the vineyard, respectively, (Rvy = Rv + Rs) and ET0 is the potential evapotranspiration. We replaced this simple radiation partitioning module (Riou et al, 1989; Lebon et al, 2003) by a numerical simulation approach for three reasons: (1) under conditions of high gap frequency we found that calculated vine transpiration could be substantially higher than measured transpiration; (2) considering the horizontal faces as opaque might overestimate the radiation absorbed by the vines, if the proportion of canopy width to row distance and the porosity are high; and (3) for the use of the model in climate impact studies for entire steep slope grape growing regions, situations described in (1) and (2) are very frequent due to the age of the vineyards and the low soil water holding capacity (SWC)
RADIATION PARTITIONING A comparison between the original radiation model of Riou et al (1989) and the new Monte Carlo approach showed very similar results for the amount of radiation received by the grapevine canopy for a porosity level of 0.25 which would be indicative of average to vigorous growing conditions (Figures 4A,C)
Summary
Grapevines are cultivated on 6 out of 7 continents, between latitudes 4◦ and 51◦ in the Northern Hemisphere (NH) and between 6◦ and 45◦ in the Southern Hemisphere (SH) across a large diversity of climates (Tonietto and Carbonneau, 2004). Wine grapes are traditionally grown in geographical regions where the growing season (April–October for the NH) mean temperature is within the range of 12–22◦C (Jones, 2006). Warming during the growing season has been observed in all studied wine regions over the past 50–60 years (i.e., Schultz, 2000; Jones et al, 2005a; Webb et al, 2007, 2011; Santos et al, 2012). Within the existing production areas, water shortage is probably the most dominant environmental constraint (Williams and Matthews, 1990) and even in moderate temperate climates, grapevines often face some degree of drought stress during the growing season (Morlat et al, 1992; van Leeuwen and Seguin, 1994; Gaudillère et al, 2002; Gruber and Schultz, 2005)
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