###### Abstract
[19] concluded that the exposure of Thompson Seedless and Napa Gamay to 40 \({}^{\circ}\)C for six consecutive days reduced berry size, as well as sugar accumulation, and delayed ripening. Other studies, for other grapevine varieties exposed to severe heat, showed similar results [20; 21]. Furthermore, several physiological processes, such as photosynthesis, are either severely reduced or inhibited at high temperatures (-35 \({}^{\circ}\)C), mostly owing to stomatal closure [16; 22; 23]. The World Meteorological Organization (WMO) defines a heatwave as a weather extreme episode with \"5 or more consecutive days of prolonged heat in which the daily maximum temperature is higher than the average maximum temperature by 5 \({}^{\circ}\)C or more\". Due to climate change, extreme weather events are projected to increase in frequency, duration and intensity [24]. Combined with the increase in mean temperature projected to occur in the future, heatwaves can indeed be seen as a major challenge that winegrowers will have to deal with in the upcoming decades. As an illustration, the 2003 heatwave in Europe highlighted the potential impact of heatwaves on viticulture [25], particularly during harvest [26]. This record-breaking heatwave in Europe may be seen as a demonstrative extreme event that is expected to occur more frequently under enhanced atmospheric greenhouse gas concentrations and anthropogenic radiative forcing [26; 27]. More recently, in 2019, there were three consecutive heatwave events in Europe (in June, July and August), with temperatures reaching 44 \({}^{\circ}\)C in some regions during June. Given the risk that heatwaves pose to viticulture and winemaking, a better assessment of the effects of these events on this sector is thereby of the utmost importance. Crop models can be a valuable tool in assessing the impact of heatwaves on viticulture [28]. These models mechanistically simulate plant development while incorporating weather, soil properties, plant data and management decisions [29]. The simulation of crop parameters, such as yields, under different pedoclimatic conditions, and abiotic stresses, are main outcomes from these models. One of their strongest advantages is the fact that they have already been applied and validated with field measurements, thus reducing the need to provide extensive experimental trials, when properly calibrated and validated. Hence, coupling dynamic (process-based) crop models with high-resolution climate, soil and plant data allows reliable yield simulations over a wide region to be produced. Despite the aforementioned advantages of these models, to our knowledge, their application to understanding the impact of heatwaves on viticulture has not been conducted yet [30]. The present study aims at analyzing the impacts of heatwaves on European viticulture, particularly on grapevine yield. As such, the objectives of the present study are fourfold: (1) to simulate recent-past yields over several main European winemaking regions, using a state-of-the-art crop model for simulating grapevines, forced by observed climate conditions over a past baseline period (control runs); (2) to carry out a sensitivity analysis to heatwaves, applying synthetic heatwave disturbances (heatwave runs); (3) to compute the regional yield differences between control and heatwave runs; and (4) to discuss potential adaptation measures to be implemented by viticulturists and winemakers, to cope with upcoming heatwaves in the near future.