Effects of agro-climatic indices on wheat yield in arid, semi-arid, and sub-humid regions of Iran

This study aimed to analyze the impact of variations of drought-related agro-climatic indices including cumulative precipitation, cumulative potential evapotranspiration, cumulative actual evapotranspiration, cumulative crop evapotranspiration, cumulative water stress, and cumulative water deficit during nine consecutive phenological stages (emergence to physiological maturity) on wheat yield in arid, semi-arid, and sub-humid regions of Iran during 1999-2018. Principal component analysis was used to recognize the main components that largely explained the variations of agro-climatic indices during different stages of the crop growing period. Then, the relationships between the major components, retrieved from principal component analysis, and the crop yield were assessed. Wheat irrigation requirements were also calculated to investigate the regional water supply-demand patterns during the crop growing period. The findings highlighted increasing impacts of cumulative precipitation, cumulative potential evapotranspiration, cumulative crop evapotranspiration, and cumulative actual evapotranspiration and decreasing impacts of cumulative water stress and deficit on wheat yield, particularly in arid and semi-arid regions. The crop yield was more affected by variations of the agro-climatic indices during the reproductive phase than the vegetative phase. Accordingly, booting to flowering in the arid region, flowering in the sub-humid region, and stem elongation to booting in the semi-arid region were the most sensitive periods of wheat to agro-climatic indices variations. Wheat irrigation requirements in arid and semi-arid regions started earlier than in the sub-humid region. From the findings, it was concluded that adjusting the irrigation schedule based on wheat irrigation requirements during the wheat growing period could help farmers to achieve a favorable wheat yield.