The global brewery sector's recent expansion has significantly increased the demand for high-quality hops, particularly late summer varieties prized for their aroma and flavor. Hops, crucial for beer's unique taste, contribute bitter acids and other compounds like essential oils and polyphenols. Changes in alpha bitter acids directly influence hop quality, and consumer preferences have shifted towards beers with intense aromas and flavors, heavily reliant on high-quality hops, a trend amplified by the craft beer boom. This increased demand contrasts with earlier preferences for lower alpha content. The global demand for aromatic hops has thus surged, necessitating a deeper understanding of how climate change will impact hop production. While some localized studies have examined the links between hop production and climate variation, a comprehensive assessment of the predicted warmer and drier climate's effects on hop yield and alpha content is lacking. The cultivation of high-quality aroma hops is limited to specific regions with suitable environmental conditions. Therefore, climate change-induced increases in heat waves and droughts pose a significant threat to hop production. Hop farmers have already begun to adapt, employing strategies such as relocating hop gardens, implementing irrigation systems, adjusting crop row orientation and spacing, and breeding more resilient varieties. However, a systematic, Europe-wide investigation of climate change's impact on hop quality and quantity remains absent. This study aims to fill this gap by analyzing the influence of temperature and precipitation on hop yield, alpha content, and cone development in key European hop-growing regions between 1970 and 2050, utilizing a newly developed model and climate projections to predict future trends and inform adaptation strategies.

Existing literature points to localized impacts of climate variation on hop production. Studies at regional scales have indicated correlations between weather patterns and hop yields or alpha-acid content. However, these studies often lack the scope of a pan-European analysis considering the interconnectedness of the global hop market. Research on adaptation measures in viticulture, facing similar challenges under climate change, offers some insights into potential strategies for hop cultivation, including irrigation techniques, row orientation adjustments, and soil management practices. The impact of drought on various crops has been investigated, providing a context for understanding water stress in hop plants. While studies on the effects of elevated CO2 on hop growth are emerging, further research is needed to fully understand its impact on yield and quality. The study addresses this gap by providing a comprehensive, large-scale assessment of the impact of climate change on the European hop industry.

To assess the impacts of climate change on aromatic hops, the study focused on key hop-growing areas in Germany, the Czech Republic, and Slovenia, representing nearly 90% of total European aromatic hop production. Five specific regions were chosen: Hallertau and Spalt (Germany), Tettnang (Germany), Zatec (Czech Republic), and Celje (Slovenia). These regions are located between 46° and 51°N and 9° and 15°E. The research utilized weather data from 59 meteorological stations across these regions. The study employed a newly developed parsimonious model to simulate the variation in hop yields and alpha-acid content based on deviations of temperature and precipitation from optimal growing season conditions. This model used historical climate data (1970-2018) and future climate projections (2021-2050) derived from climate models to estimate changes in yields and alpha-acid content under varying climate scenarios. The model’s inputs included air temperature and precipitation records. The statistical correlation between the model's predictions and observed hop yields and alpha-acid content was analyzed to assess the model's accuracy and reliability. Further analysis included comparing changes in hop yield, alpha-acid content and cone development between two periods: 1971-1994 and 1995-2018 to quantify historical trends, followed by model projections for 2021-2050 under different climate change scenarios to predict future changes across Europe. The study employed statistical methods to analyze the relationships between climatic variables and hop production parameters, allowing for a quantitative assessment of climate change's impact.

Analysis of hop yields between 1971-1994 and 1995-2018 revealed a significant decline, ranging from 9.5% to 19.4% across the five study regions. Zatec showed relatively stable production, while Celje and Spalt experienced the most significant drops. Alpha-acid content also decreased substantially in all regions (10.5% to 34.8%). The onset of the hop growing season advanced by approximately 13 days between 1970 and 2018. The model indicated a strong correlation between precipitation and hop yields, and between temperature and alpha-acid content. Years with extreme weather conditions (drought or heat) led to lower yields and alpha-acid content. Model projections for 2021-2050 predicted a yield decline ranging from 4.1% to 18.4% and an alpha-acid content decrease of 20% to 30.8%, with the most severe reductions in southern regions. Analysis of changes across Europe supports these findings, projecting declines in both yield and alpha-acid content in all major hop-growing regions. The most dramatic declines were predicted for southern European countries (Portugal, Slovenia, and Spain). These findings strongly indicate a negative relationship between increasing temperatures, reduced precipitation, and hop productivity. While deficit irrigation has been studied as a mitigating factor, it did not eliminate yield reductions in other regions. Alpha-acid content was also affected by temperature and sunshine duration, leading to significant drops in some years. The most profound impacts are observed in periods of extreme conditions in all regions, implying that production losses in some areas cannot be compensated by increases in other areas.

The findings demonstrate a clear climate-induced decline in the quantity and quality of European aroma hops. The significant decreases in both yield and alpha-acid content, supported by both historical data analysis and model projections, highlight the vulnerability of this crucial agricultural sector to climate change. The earlier ripening period, driven by rising temperatures, shifts the critical maturation phase into warmer conditions, negatively affecting alpha-acid development. The strong correlations between climate variables (temperature, precipitation) and hop production parameters underscore the direct impact of climate change. The model's projections paint a concerning picture for the future of European hop production, especially in southern regions, but also in others if mitigation and adaptation measures are not implemented. The projected decline in alpha-acid production is particularly significant, as it directly affects beer quality and consumer preferences. The observed and projected declines have significant economic implications for the brewing industry and the livelihoods of hop farmers.

This study clearly demonstrates a climate-induced decline in the quality and quantity of European aroma hops. Urgent adaptation measures are necessary to stabilize international market chains. Future research should focus on developing and implementing climate-smart agricultural practices, exploring more resilient hop varieties, and enhancing water management strategies. Further investigation is also needed into the potential of CO2 fertilization to mitigate negative impacts. Addressing these challenges will be crucial to secure the future of European hop production and the brewing industry’s global supply chains.

The model used in this study is based on a simplified representation of complex biological processes, and thus, uncertainties are involved in future projections. The model's accuracy depends on the quality and availability of climatic data, which may vary across different regions and time periods. The study primarily focused on specific hop-growing regions, and results may not be fully generalizable to all European hop-growing areas. Future research could incorporate more detailed physiological information, advanced modelling techniques, and a wider range of climate scenarios to increase the accuracy of predictions and improve understanding of adaptation strategies.