From the report “Weakly hardened winter cereals“, published in the JRC MARS Bulletin Crop monitoring in Europe by the European Commission.
Hardening is the bio-physiological process of winter cereals which transforms the cellular starch into glucose, thereby raising the freezing point of the cellular liquids and increasing the low-temperature tolerance of the plants.
In December, weather conditions were warmer than usual in most parts of Europe. Moreover, the warmest December conditions on our record were observed in major parts of western, central and south-eastern Europe. Colder-than-usual weather prevailed in northern, eastern and central Europe during the first two weeks of January. Drier-than-usual conditions prevailed in the eastern Iberian Peninsula, southern France, Italy, Romania and many regions of southern and central Europe. Abundant rainfalls were recorded in the British Isles, resulting in major flooding events.
In the British Isles (except eastern Scotland), the Iberian Peninsula and France, as well as in the Mediterranean region, the Balkan Peninsula and surrounding areas of the Black Sea, winter crops have not gained low-temperature tolerance at all, due to the fact that this region experienced mostly warmer-than-usual daily temperatures since early December. The weakly hardened crops run the risk of incurring frost-kill damage in the event of a sudden freezing air intrusion.