Impact of Drought on the Yield of Rainfed Wheat and Barley Across Different Climates of Iran

Drought events in dry and semi-dry climates are of great importance due to the extensive and costly effects they have on various economic and environmental sectors. In recent years, the impact of this natural phenomenon has been very evident, especially on rainfed crops. In this study, the impact of drought on two strategic rainfed crops of Iran (wheat and barley) was evaluated. Since the agricultural sector is vulnerable to climate change, it is very important to identify the most appropriate tools to monitor the impact of climate on the productivity of agricultural products. Therefore, evaluating the effects of drought indicators is the most effective tool. Various drought indicators have been used to evaluate the impact of drought on rainfed wheat and barley yields across different climates of Iran, which include; the Standard Precipitation Index (SPI), Standard Precipitation Evaporation and Transpiration Index (SPEI), Standard Soil Moisture Index of the upper two layers (SSI1 and SSI2), Standard Multivariate Drought Index including; MSDI1 was based on precipitation and reference evapotranspiration (P&ETref), MSDI2 was based on precipitation and soil moisture in the first soil layer (P&SM1), and MSDI3 was based on precipitation and soil moisture in the second soil layer (P&SM2). Two sets of crop performance data at different spatial scales and time periods were used in the analysis. The results showed that the drought indices calculated in different time scales of SPI and SPEI had the highest correlation with rainfed wheat and barley yields in semi-dry (0.7 and 0.77), dry (0.68 and 0.64), very dry (0.63 and 0.61) and humid (0.64 and 0.52) climates, respectively. Also, the results showed that different patterns of response of crops to drought occur depending on the climate type, the period of the year, and the time scale of the drought.