Relationship between ENSO and winter-wheat yields in Sonora, Mexico

Winter-grown wheat is one of the main cultivates in river-irrigated valleys of the state of Sonora, northwest Mexico. Although largely determined by technological improvements and management, wheat yields may still reflect year-to-year variations partially determined by climatic factors, including the extreme phases of El Ni o-Southern Oscillation. We analyzed time series of yearly wheat yields for five locations; yield residuals were obtained from a logistic model in order to eliminate long-term trends due to technological development. The series of residuals were found to be significantly correlated to at least one other series. This common variability was extracted by means of Principal Component Analysis. The first component accounted for a 63% of total variance. The amplitude time series of this component was compared to indices of ENSO. El Ni o (La Ni a) episodes seem to result in an increase (decrease) in wheat yields, which is consistent with previous reports of an increased (decreased) precipitation over northwest Mexico during these events.