###### Abstract  
Extreme heat events or heatwaves can be particularly harmful to grapevines, posing a major challenge to winegrowers in Europe. The present study is focused on the application of the crop model STICS to assess the potential impacts of heatwaves over some of the most renowned winemaking regions in Europe. For this purpose, STICS was applied to grapevines, using high-resolution weather, soil and terrain datasets from 1986 to 2015. To assess the impact of heatwaves, the weather dataset was artificially modified, generating periods with anomalously high temperatures (+5 \({}^{\circ}\)C), at specific onset dates and with specific episode durations (from five to nine days). The model was then run with this modified weather dataset, and the results were compared to the original unmodified runs. The results show that heatwaves can have a very strong impact on grapevine yields. However, these impacts strongly depend on the onset dates and duration of the heatwaves. The highest negative impacts may result in a decrease in the yield by up to \(-35\%\) in some regions. The results show that regions with a peak vulnerability on 1 August will be more negatively impacted than other regions. Furthermore, the geographical representation of yield reduction hints at a latitudinal gradient in the heatwave impact, indicating stronger reductions in the cooler regions of Central Europe than in the warmer regions of Southern Europe. Despite some uncertainties inherent to the current modelling assessment, the present study highlights the negative impacts of heatwaves on viticultural yields in Europe, which is critical information for stakeholders within the winemaking sector for planning suitable adaptation measures. heatwaves; viticulture; vineyards; Europe; climate change; yield; pinot noir 20202  
Temperature is a key factor affecting plant growth and development rates [6]. For grapevines, air temperature is considered to be a fundamental factor controlling the main physiological processes, phenological timings and overall productivity and quality [7]. Although other atmospheric variables, such as precipitation, humidity and solar radiation, also play an important role in grapevine development, temperature is considered to be the main factor. In effect, grapevine physiology and fruit metabolism/composition are highly influenced by the thermal conditions during the growing season [8]. For adequate grapevine growth, phenological development and yield attributes [9], there are indeed optimum temperature ranges and thermal thresholds, establishing both lower and upper limits, which are, however, variety-dependent. One of the most well-known climatic requirements of the grapevine is the 10 \({}^{\circ}\)C base temperature for heat accumulation, which is needed for the onset of its vegetative cycle [10; 11; 12; 13; 14; 15]. Over the last decades, most research was aimed at the lower thermal limits for heat accumulation, which has traditionally been a major concern for winegrowers. Nonetheless, the effect of high temperatures on grape physiology is likely to become more important in the future, due to global warming [15]. Hence, a better analysis of the upper thermal limits for grape development and physiology is of foremost relevance. It is known that if air temperature exceeds a given upper threshold (e.g., 35 \({}^{\circ}\)C) at certain critical periods of grapevine development, negative impacts on grapevine should be expected [16]. In effect,  
Figure 1: Selected wine regions in Europe (18), highlighted by a black line contour, and their corresponding designations. Other wine regions are also outlined, with different color shadings for different countries. extreme heat can be particularly harmful to grapevines. Grapevines growing under severe heat stress experience a significant decline in productivity, e.g., due to limitations in photosynthesis [17], as well as injures under other physiological processes [18]. As an example, a study carried out by [PERSON] et al.