Simulating the effect of the North Atlantic Oscillation on frost injury in winter wheat

Climate and weather variability affect agricultural crop production. The North Atlantic Oscillation (NAO) is the variation in air pressure difference in the northern Atlantic Ocean. A positive NAO index with higher than normal air pressure near the Azores and lower than normal near Iceland results in warm and wet winters in northwestern Europe. A negative NAO index gives opposite climatic effects in this region. We determined the effect of the NAO on the risk of frost injury in winter wheat for conditions that represent northwestern Europe by applying the FROSTOL model to dynamically simulate hardening, de-hardening and other physiological processes determining frost tolerance and frost injury in winter wheat. This model uses soil surface temperature and snow cover as driving variables. In total, 53 winter seasons from 1957-58 to 2009-10 were simulated to account for historical trends and variations in the NAO. Monthly and seasonal mean NAO indices for all years within this period were categorised into positive, neutral or negative phases. The winter wheat simulations included 3 locations in Norway (Apelsvoll, angstrom s and Kvithamar), 2 wheat frost tolerance types and 3 planting dates. The results showed that negative NAO phases, especially in February and March, increased the risk of frost injury in winter wheat. The risk of frost injury was higher at Apelsvoll and angstrom s than at Kvithamar, especially in negative NAO phases or after early planting. The results obtained can be used to design crop management practices and systems with higher production security.