Many researchers around the world have reported a gradual increase in mean annual temperature. Yet, there are some reports of a reduction in this parameter. In this study, we investigated the long-term trend of mean annual temperature at 34 synoptic stations in Iran. | Turk J Agric For 30 (2006) 439-448 © TÜB‹TAK Time Trend in the Mean Annual Temperature of Iran Bijan GHAHRAMAN Irrigation Department, College of Agriculture, Ferdowsi University of Mashhad, Mashhad 91775, IRAN Received: Abstract: Many researchers around the world have reported a gradual increase in mean annual temperature. Yet, there are some reports of a reduction in this parameter. In this study, we investigated the long-term trend of mean annual temperature at 34 synoptic stations in Iran (2 stations in cool humid climates, 14 stations in temperate humid climates, 11 stations in steppe climates, and 7 stations in desert climates, based on the Koppen climatic division) with a minimum record of 30 years by Student’s t-test. Results showed that there was a positive trend in 50% of the stations, while 41% of stations had a negative trend. Considering the significance level (α = 5%), there were 3 trend zones for mean annual temperature in Iran, . positive trend, negative trend, and zero trend; however, it was difficult to define a specific spatial scheme for such a division. The results were supported by the MannKendall method, while low harmony was found with the Wald-Wolfowitz test. As far as record length is concerned, during a common time period (1968-1998), 65% of the stations showed a positive trend, while 32% of them followed a negative trend. There were some shifts from one trend to another for some of the stations in the study, yet with no well-defined spatial structure. In this case, and at the 5% level of significance, 44%, 15%, and 41% of the stations had a positive trend, a negative trend, and zero trend for the parameter of the study, respectively. In general, the behavior of trend direction was different for different climates and no specific pattern was found. Based on the results, one may hypothesize that in the future more regions will experience higher temperatures. Some stations did not show any significant trend, yet their .
