Soya bean yield variability in the Argentine Pampas in relation to synoptic weather types: monitoring implications

This paper analyses the soya bean yield variability in the Argentine Pampas in relation to the atmospheric circulation patterns in southern South America. The region studied is the main soya bean production area in Argentina and contributes a high percentage to world trade in soya beans and their by‐products. Two datasets were used: the soya bean yield series of 58 provincial districts and daily average fields of 1000 and 500 hPa geopotential height corresponding to the NCEP_Reanalysis 2 in the period 1979–2001. Adverse impacts on final yield may be mainly associated to weather types (WTs) related to intense rainfall during harvest time (April and May) and to structures which favour stability and warm advection in the summer at lower levels. The thermal effect on soya bean may be observed in the WTs whose configuration of anomalies favours the incursion of cold air at the lower levels contributing to low temperatures during seed germination and early vegetative growth stages. Positive impacts may be associated with WTs that reduce thermal stress during flowering and pod set stages (summer) and WTs which favour stability at harvest time (April). In general terms, atmospheric circulation structures have been identified as elements which may be added to the set of climate predictors to explain a part of interannual yield variability. The structures found have direct implications for short and middle term forecasts. They constitute a primary element for the monitoring of the growing season of the soya bean crop and for planning strategies. Copyright © 2009 Royal Meteorological Society