Projected impacts of sowing date and cultivar choice on the timing of heat and drought stress in spring barley grown along a European transect

Barley is one of the most important cereals for animal and human consumption. Barley heading and grain filling are especially vulnerable to heat and drought stress, which are projected to increase in the future. Therefore, site -specific adaptation options, like cultivar choice or shifting sowing dates, will be necessary. Using a global climate model ensemble and a phenology model we projected spring barley heading and maturity dates for 2031-50 for climatically contrasting sites: Helsinki (Finland), Dundee (Scotland) and Zaragoza (Spain). We compared the projected future heading and maturity dates with the baseline period (1981-2010) and described corresponding heat and drought stress conditions and how they were affected by adaptation options, i.e. shifting the sowing date by + /-10-20 days, choosing early or late heading cultivars or combining both adaptation options, with agroclimatic indicators. At all sites and sowing dates, heading and maturity in 2031-50 occurred earlier (up to three weeks with earliest sowing) than in the baseline period. Along the European transect, the projected heading and grain filling periods were hotter than under baseline conditions but advancing heading alleviated heat stress notably. Different indicators signaled more severe drought conditions for 2031-50. At Helsinki, delayed heading periods were exposed to less drought stress, likely because the typical early summer droughts were avoided. At Zaragoza, fewer, yet more intense, rainfall events occurred during grain filling of the early cultivars. Only under scenario RCP4.5, heading and grain filling periods at Dundee were slightly wetter for the early cultivars. Our study provides a unique overview of agroclimatic conditions for heading and grain filling periods projected for 2031-50 along a climatic transect and quantifies the effects of different adaptations for spring barley. The approach can be extended by coupling the agroclimatic indicators with crop modelling.