Vulnerability of hop-yields due to compound drought and heat events over European key-hop regions

Authors: Vera Potopová and Ondrej Lhotka and Martin Možny and Marie Musiolková
Journal: International Journal of Climatology
Year: 2020

Compound climate events in which only one variable is extreme (e.g., either hot but no drought or extreme drought but not hot) and events in which both variables are extreme (e.g., drought and heat waves) may have different impacts on hop yields and alpha‐bitter acid contents. Increasing occurrences of compound drought and heat events have led to increased income variability for beer production, and also affecting the major hop growers across Europe (EU). Our study includes the key hop‐growing regions across the EU such as Hallertau (Germany); Úštěcko, Žatecko and Tršická (Czech Republic); Kent (Great Britain); Alsace (France); Lublin (Poland); Koroška (Slovenia) and León and Galicia (Spain). For these regions, we used the concurrent bivariate return period to model the joint probability distributions of daily precipitation and maximum temperature extremes and to provide risk assessments for concurrent drought‐heat waves during the hop‐growing season. We estimated the risk of lower yields from hop cones based on concurrent dry‐cool, dry‐hot, wet‐cool and wet‐hot modes over the target areas. The results show that longer and more severe drought and heat wave concurrences have increased more frequently than shorter concurrences. The degree of risk was estimated as being higher over the extensive hop‐growing areas in the Czech Republic and Germany. A total of 22.4, 12.5 and 7.2% of EU areas with conditions suitable for commercial hop production fell into the moderate, high and very high yield loss risk categories, respectively. Integrating the damage between April and August indicated that more than 62.7% of total yield losses were due to high temperatures under dry conditions and that 21.5% of the yield losses were due to dry‐cool conditions in the top hop‐farming regions. The hotter European droughts caused decreases in noble aromatic hops by 29–68%. This indicates that hop yields are very vulnerable to these events due to a slower rate of adaptation of hops compared to field crops.