Can Swiss wheat varieties escape future heat stress?

Climate change-induced heat waves represent a severe threat to future global crop production. The extent of heat stress for agricultural crops depends on the co-occurrence of heat periods and heat sensitive phenological stages. Using the Wang and Engel phenology model and the most recent climate change projections for four sites across the Swiss Central Plateau, we estimated future heat stress exposure in Swiss wheat production and tested the potential of winter wheat genotypes with differing phenological characteristics to escape future heat periods. Across all genotypes, heat stress days (T-max >= 30 degrees C) during the temperature sensitive stages of flowering and early grain filling increased from an average of 1.5 heat days in 1982 2006 to 2.1 by 2075 2099 with RCP2.6 (with climate change mitigation) and to 3.6 by 2075 2099 with RCP8.5 (without climate change mitigation), respectively. Across all genotypes and locations, a considerable escape from future heat periods was modelled due to a mainly temperature-driven advancement in the phenological development. Under both RCP scenarios, we predicted lower exposure to heat stress for early varieties than for late varieties. However, under the RCP8.5 scenario, for each location, heat stress exposure for early varieties was still projected to be higher by 2075 2099 than for late varieties under current conditions. Further, heat stress exposure was considerably increased at locations with cooler spring conditions, slowing down the early season phenological development and resulting in late heading dates. Our findings imply needs for a regionally adequate cultivar selection as well as for phenological adaptions and heat tolerance traits in Swiss wheat breeding to adapt to future climate change and regional climatic differences. Different strategies of breeding adaptations and their trade-offs are discussed.