Assessing the Vulnerability of Agricultural Areas under Climate Change in Europe through a Heat Stress Index Approach

Climate change poses a significant threat to agriculture, primarily through yield losses due to droughts and heat waves. The flowering phase of most crops is a critical period during which they are highly susceptible to heat, resulting in long-term damage and substantial yield reduction. Significant heat-induced yield cuts have already been observed in Europe, especially during the frequent and widespread heat waves occurring in the years 2018 to 2022.

By imposing the large-scale atmospheric circulation of the 2018 to 2022 heatwaves onto CMIP6 projections, the impact of such a multi-year event within future climate is made tangible as a storyline (Sánchez-Benítez et al., 2022). The +4K storyline, which gives a flavour of possible atmospheric conditions in the 2090s in the ssp370 scenario, indicates a potential increase of up to 7°C during the flowering phase of major crops in Europe. Using these storylines, we evaluated the impact of such a heatwave on cereal production in Europe under a warmer climate.

To achieve this, we developed a heat stress index, which gauges the amount of stress experienced by crops due to heat exposure during flowering relative to unstressed conditions. This index was then applied to the dynamically downscaled nudged storylines over the European domain and evaluated for major cereal crops (maize and wheat). As part of this evaluation, we modelled how a changing climate would affect planting dates and the area suitable for growing winter cropsand investigated the potential impact of heat on different crop cultivars.

In 2021, we estimate that approximately 4% of cropland in Europe experienced severe heat stress (i.e., yield losses of up to 50%) due to heat waves during flowering. Extrapolating to a scenario with global warming of +4 K, we show that almost 80% of the total European crop area for maize could be affected by heat stress, with 30% of the area experiencing a severe heat stress. This could lead to a 20% yield reduction across Europe. In south-eastern Europe, where the 2021 heatwave was particularly intense, 40% of the harvested area would be severely affected, leading to a yield loss of 32% relative to current conditions.

Our investigation of different stress vulnerabilities shows that some crop varieties may exhibit minimal stress while others face severe damage, leading to considerable intra-crop variability in yield reduction. Planting date plays a major role in the impact of heat stress, since an earlier planting shifts the sensitive window during which the plant is flowering to earlier in the year. For winter crops, such as winter wheat, the increased temperatures in winter could lead to a reduction of the winter wheat growing area of 50% by 2093. Addressing these challenges will require proactive management changes, including strategic decisions on planting dates, crop, and variety selection.

Sánchez-Benítez, A., Goessling, H., Pithan, F., Semmler, T., Jung, T., 2022. The July 2019 European Heat Wave in a Warmer Climate: Storyline Scenarios with a Coupled Model Using Spectral Nudging. Journal of Climate.