Rainfed wheat and barley production are low in semiarid regions of northeast of Iran where the rainfall is limited and highly variable. The objective of this study was to investigate wheat and barley grain yields historical trend and its relation to rainfall in six agricultural centers (Mashhad, Birjand, Bojnourd, Sabzevar, Gochan, and Torbat-h) in semiarid regions of northeast of Iran. According to local sowing and harvesting date of rainfed wheat and barley for all locations, growth period of both crops were divided to three periods including early growth period, mid growth period, and end of growth period. Grain yield trend and the association between cumulative rainfall amounts of each time period with long term average yield of each study location was calculated. The results showed that the highest raise in average yield of rainfed wheat and barley obtained in Gochan, Torbat-h, and Birjand where higher annually rainfall occurs compared to other locations. In addition, the end of growth period indicated highest correlation between rainfall amounts and average yield for both crops in all locations. It is concluded that rainfed wheat and barley yield could be increased by changing sowing dates or employing supplement irrigation in semiarid regions of northeast of Iran.

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