On soil moisture deficit, low precipitation, and temperature extremes impacts on rainfed cereal productions in Iran

In this study, rainfed wheat and barley yields response to severity and persistence of cold temperature extremes in the January-February-March (JFM) and high temperature, low rainfall, and soil water shortage extremes in the October-November-December (OND) and March-April-May (MAM) was evaluated. For this purpose, the associations between the yields and the extreme indices were tested using Pearson's correlation coefficient for 10 sites located in the western Iran over 1982-2013. The FAO-56 soil water balance model was employed to develop the soil water deficit extreme indices. The impacts of extremes on the yields were also investigated under El Nino-Southern Oscillation (ENSO) phases. The yields were anti-correlated significantly (p<0.05) with the soil water shortage and rainfall deficit extreme indices, but not with the temperature-related extreme indices, for the majority of sites. On average, a more negative association also existed between the yields and the soil moisture-related indices relative to the rainfall and temperature extreme indices. The yields seem, therefore, to be more adversely impacted by agricultural droughts. Compared with the OND extremes, the high temperature, precipitation shortage, and soil water deficit extremes in MAM had more negative effects on the yields. This can be attributable to strong sensitivity of reproductive processes commonly occurring during MAM to such stresses. In most cases, the yields were more adversely influenced by the short-term extremes. The results also revealed that more frequent occurrence of high temperature and drought-related extremes during La Nina can well explain the substantial yield loss in cold ENSO years.