Climate-induced decline in the quality and quantity of European hops calls for immediate adaptation measures

Beer is the world's third most widely consumed beverage after water and tea, and traditional beer brewing in central Europe dates back at least to the Neolithic period circa 3500–3100 BC. In addition to water, malting barley and yeast, a much more expensive hop is needed to give beer its incomparable taste. The specific hop aroma emerges from its bitter acid content and many other compounds, including essential oils and polyphenols. Changes in alpha bitter acids affect the quality of hops, and there has been a recent change in consumer preference towards beer aromas and flavors that heavily depend on high-quality hops. Amplified by the ongoing craft beer popularity, this trend contrasts with previous demands for lower alpha content. The recent craft beer expansion therefore not only triggered new microbreweries but also boosted the demand for aromatic hops globally. Although linkages between hop production and climate variation have been reported at local to regional scales, relatively little is known about the possible, direct and indirect, effects of a predicted warmer and drier climate on the yield and alpha content of hops. Since the cultivation of high-quality aroma hops is restricted to relatively small regions with suitable environmental conditions, there is a serious risk that much of the production will be affected by individual heat waves or drought extremes that are likely to increase under global climate change. Hop farmers can and have responded to climate change by relocating hop gardens to higher elevations and valley locations with higher water tables, building irrigation systems, changing the orientation and spacing of crop rows, and even breeding more resistant varieties. Changing the orientation of crop rows and combining irrigation with water-saving soil management practices have proven to be effective adaptation measures in viticulture. It is important that the generative phase of hop plants occurs only in the appropriate photoperiod when sunshine duration is decreasing. This can be achieved by slowing plant growth via growth inhibitors or by building protective shading structures; which is, however, quite expensive. There is a similar problem in vineyards where shading by agrovoltaic panels has been introduced. The higher probability of droughts can be partly mitigated by less frequent tillage and cultivation of hop fields, changes in fertilization and the use of row cover crops to support root growth. A systematic and European-wide investigation of the impact of ongoing and predicted climate change on the quality and quantity of aroma hops is, however, still missing. Here, we show how temperature and precipitation control the yield, alpha content and cone development of aroma hops in Germany, the Czech Republic and Slovenia between 1970 and 2050 CE. We simulate the effect of weather conditions on hop yield and alpha content with a newly developed model. Using simulations of future climate, we predict yield and alpha content. We then discuss how hop farmers can implement innovative adaptation measures to stabilize international markets under predicted global warming.

Prior studies reported linkages between hop production and climate variability at local to regional scales, including effects of heat and drought on yield formation and alpha acids. Adaptation strategies analogous to viticulture, such as changing row orientation and integrating irrigation with water-saving soil management, have shown effectiveness. Deficit irrigation experiments in Washington State (USA) quantified yield reductions under water stress, with 60% irrigation causing 19–33% reductions over two years and 80% irrigation causing −14% to +2% changes, while alpha-acid concentrations were not affected. Additional research highlights the roles of plant health, genetics and epigenetics, irrigation systems, harvest timing, site and soil conditions, and agronomic practices on hop yield and alpha content. Broader climate projections indicate increased frequency of agricultural droughts, especially in southern Europe, underscoring the need for climate-smart agriculture.

The study focused on major European aroma hop-growing regions covering almost 90% of the continent’s aroma hop acreage, selecting Hallertau, Spalt and Tettnang (Germany), Zatec/Saaz (Czechia), and Celje (Slovenia), located between 46–51°N and 9–15°E. A parsimonious model was developed to simulate interannual variation in hop yield (t/ha) and alpha content (%) from meteorological inputs, specifically deviations of precipitation totals and air temperatures during the growing season from optimal conditions. Observational datasets included records from 59 weather stations and phenological observations (e.g., date of cone development, BBCH 71). Statistical relationships were assessed between precipitation anomalies in the growing season and yield (r = 0.41–0.73; p < 0.01), and between average temperature (and sunshine duration) at heading and alpha content (r = 0.61–0.78; p < 0.01). Sunshine duration at heading was positively correlated with alpha content. The model was driven by historical observations (baseline approximately 1981–2018; medians reported for 1989–2018) and by future climate projections (2021–2050) using three GCM runs under the RCP 4.5 scenario to estimate changes in yield, alpha content, and alpha yield (kg/ha) across the selected regions and an expanded set of 59 European and UK sites. Ancillary datasets referenced include surface radiation products (e.g., SARAH) and local-scale daily climate scenarios (e.g., ELPIS), with data sources documented in a public repository.

• Comparing 1971–1994 to 1995–2018, average annual hop yields decreased by 0.13–0.27 t/ha. Regional percent declines in average yield after 1995: Celje −19.4%, Spalt −19.1%, Hallertau −13.7%, Tettnang −9.5%, with Zatec remaining stable (change ~0.05 t/ha). • Alpha content declined significantly across all regions by 0.46–1.86% absolute. Percent declines in average alpha content: Celje −34.8%, Hallertau −15.6%, Tettnang −15.0%, Spalt −11.5%, Zatec −10.5%. • Phenology advanced: the onset of the hop growing season shifted 13 days earlier (1970–2018). After 1995, cone development (BBCH 71) occurred earlier relative to 1971–1994 by 31 days (Celje), 22 days (Zatec), 16 days (Hallertau and Spalt), and 13 days (Tettnang). This shift moved ripening into a warmer period, negatively impacting alpha content. • Extreme years: yield declines >30% occurred in 2000 and 2003; alpha content decreases >40% occurred in 2006 and 2015. • Model diagnostics: yield correlated with deviations of precipitation totals from optimal growing-season conditions (r = 0.41–0.73; p < 0.01). Alpha content correlated with average temperature at heading (r = 0.61–0.78; p < 0.01) and positively with sunshine duration at heading (p < 0.01). The lowest yields were linked to precipitation deficits, while the lowest alpha values were caused by extremely high temperatures; temperature and light extremes in 2006 led to sharp drops in alpha content across all regions. • Projections (2021–2050 vs 1989–2018): yields decline by 4.1–18.4%, alpha content by 20–30.8%, and alpha yield by 25.3–39.5%. Strongest declines are expected in southern regions (Tettnang, Celje), with more moderate decreases in northern sites (Hallertau, Spalt, Zatec). • Europe-wide assessment (EU and UK; 59 sites; 3 GCMs; RCP 4.5): yields decline by 12–35% in 2021–2050 across major regions; Slovenia, Portugal, and Spain show the most pronounced declines. Alpha content is projected to decrease considerably across all regions; moderate decreases in Germany, Czechia, and Poland; strongest declines in Portugal, Slovenia, and Croatia.

The findings demonstrate that ongoing warming and more frequent droughts have already advanced hop phenology, shifted ripening into hotter parts of the season, and reduced both yield and alpha content, thereby threatening the quality and quantity of European aroma hops. The modeled sensitivities quantify key drivers: precipitation deficits depress yields, while high temperatures around heading reduce alpha content, with sunshine exerting a positive but potentially heat-exacerbated influence. The projected mid-century declines underscore vulnerability of southern growing areas and indicate that inter-regional compensation during extreme years is limited when heat and light extremes are widespread. To address these challenges, adaptation measures discussed include relocating hop gardens to wetter and cooler micro-sites (elevations, valleys with higher water tables), deploying and optimizing irrigation (e.g., drip systems with advanced scheduling), modifying row orientation and spacing, applying water-saving soil management and cover crops, using growth regulators or shade structures to manage phenology, and breeding or selecting more heat- and drought-resilient varieties. The sector will also need to consider climate-smart agricultural strategies to sustain productivity, reduce emissions, and enhance resilience, alongside potential expansion of aroma hop area to buffer expected declines in alpha content and yield.

Climate change has already caused significant declines in European aroma hop yields and alpha content, with earlier phenology shifting ripening into warmer conditions that degrade quality. Model-based projections indicate further reductions in yield (4–18%), alpha content (20–31%), and alpha yield (25–40%) by 2050 under RCP 4.5, with southern regions being most affected. Immediate adaptation is needed across cultivation practices, site selection, irrigation, canopy and phenology management, and breeding to stabilize supply chains for a growing global brewery sector. Expanding aroma hop acreage by approximately 20% may be required to compensate for projected alpha content and production declines. Continued improvement of observations, process understanding of hop physiology (including CO2 effects, vernalization, and dormancy), and modeling will support more targeted and effective adaptation strategies.

Uncertainties arise from model structure and climate projection inputs (limited to three GCM runs and RCP 4.5 for 2021–2050), as well as from incomplete understanding of physiological responses. Elevated CO2 could partially offset drought impacts by improving water-use efficiency and growth, but its net effect on hops remains under investigation. External, non-climatic factors—plant health, genetics/epigenetics, irrigation design, harvest maturity, site and soil characteristics, and agronomic practices—also influence yield and alpha content and may confound climate signals. More detailed in situ measurements and seasonal climate observations from hop gardens are needed to refine models and reduce uncertainty. The regional focus on Germany, Czechia, and Slovenia, while covering most European aroma hop area, may limit generalizability to other regions with different management and environmental contexts.