Summer rainfall and wheat grain quality: Relationships with the North Atlantic Oscillation Peter S. Kettlewell 1 , David B. Stephenson 2 , Mark D. Atkinson 1 and Philip D. Hollins 1 1 Crop and Environment Research Centre, Harper Adams University College, Shropshire 2 Department of Meteorology, University of Reading There have been numerous studies of the rela- tionships between climate and wheat yield weight of grain per unit area of ground) e.g. Hooker 1922; Chmielewski and Potts 1995). Incontrast,therehasbeenrelativelylittlework examiningtheeffectofclimateonthe quality of the grain produced, i.e. suitability for use in food production and consumption. Recently, Kettlewell et al. 1999) have shown that the qualityofUKwheatgrainatsummerharvestis strongly influenced by the North Atlantic Oscillation NAO)intheprecedingwinter.The NAO is a large-scale alternation in air pressure between northern and southern regions of the North Atlantic Ocean recently reviewed by Wanner et al. 2001). By exploring the effect of the NAO on wheat quality, we have discovered that the winter NAO influences the following summer England and Wales rainfall. In this article we first discuss the relationships betweensummerclimateandwheatquality,we then describe the evidence for the effect of the winter NAO on summer rainfall amount, and finally consider possible predictive skill of the NAO forrainfallamount. Climate and wheat quality Some general aspects of wheat development are described in this section, together with the importance of wheat quality in the UK, before theeffectofclimateisdiscussed.Almostallthe wheatinBritainissowninautumnandwinter, between September and December, rather than in spring Finch et al. 2002). There is a long vegetative period after germination when leaves and side shoots emerge in succession untilspring.Developmentofcropssownatdif- ferent dates is gradually synchronised by the increasing daylength in spring. The stem extendsinspringandtheearhead)emergesin late May/early June. Grain growth starts at flowering anthesis), and this occurs in June in virtually all crops. Grain growth ceases in late July or August and is followed by a ripening period when the grain loses moisture before harvest. In England, where the great majority of UK wheat is grown, harvest normally takes place in August, although in Scotland harvest oftenextendsintoSeptember. ThequalityofwheatgrowninBritainwasof relatively little consequence until accession to the European Economic Community EEC)in 1973.Beforethis,mostofthewheatforbaking into bread was imported from North America. The EEC imposed import tariffs which made import of North American wheat prohibitively expensiveformillingintothemajorityofbread flour Butler 1986). Technological changes to the baking process also allowed more British wheat to be used for bread making Farrand 1972).Thiscreatedastrongincentivetomoni- tor the quality of British wheat to inform the wheat industry about the quality of raw mate- rial available for milling and baking. Thus a national survey of wheat quality began follow- ing the harvest in 1974, undertaken by the Home-Grown Cereals Authority 1974). The surveyhascontinuedeveryyearandcoversthe UK, although relatively few samples are taken from Scotland or Wales and usually none from NorthernIreland. There are several aspects of quality mea- sured in the survey, but not all aspects are equally important to all end-users of wheat grain. One quality characteristic, however, is 1 Weather Vol.58 April2003