Precipitation and temperature are two main climatic factors that influence crop productivity in arid and semi-arid areas. Study of the variability in these variables is thus important especially under dryland farming. In the present study, we evaluated the relationship between minimum, maximum, and mean temperatures; precipitation; and dryland wheat yield in northwest of Iran. The association between long-term weather data and dryland wheat yield for the time period bracketing 1990 and 2004 was investigated in seven stations (Ahar, Tabriz, Maragheh, Myaneh, Urmia, Khoy, and Makou) homogenously distributed over the study region. Aridity index (AI) was also calculated and its relationship with wheat yield was studied. Results showed that AI significantly decreased in the whole region (except for Urmia) with the highest variation in Maragheh and Myaneh. Increase in temperature was the major contributing factor to the increasing AI. Association between weather variables and dryland wheat yield at annual, seasonal, and monthly scales showed different results. At seasonal scale, spring was the main season affecting wheat yield. Also, at monthly scale, January, April, and May had more important role in wheat yield variation compared to the other months. The association between dryland wheat yield and weather variables was stronger in Maragheh and Myaneh. At the end, it was concluded that wheat yield was more affected by the variability in the climate in East Azerbaijan compared to that in West Azerbaijan. [ABSTRACT FROM AUTHOR]