Bijan Ghahraman - Irrigation Department, College of Agriculture, Ferdowsi University of Mashhad, Mashhad
Hadi Shirgholami

Many researches around the world have indicated the gradual increase in mean annual temperature. Yet there are some reports on reduction of this parameter, In this research we investigated the long time trend of mean annual temperature in 34 synoptic stations of Iran (2 stations in Cool humid climate, 14 stations in Temperate humid climate, 11 stations in Steppe climate, and 7 stations in Desert climate-based on the Koppen climatic division) with a minimum record of 30 years by minimum square error and also Man-Kendall methods (Wald-Wolfowitz method was not in harmony with these two ones). Result showed that for the whole time horizon of data, there was a positive trend in 59% of stations, while 41% of stations had negative trend. Considering significance level resulted into 3 zones of positive, negative, and without trend for mean annual temperature in Iran. However, it was hard to define a specific spatial scheme for such a division. By an another approach, we proceeded with a common time period of 1968-1998 for all stations, In this case, 68% of stations showed a positive trend, while the other 32% followed a negative trend. There were some shifts for one trend direction to another one for some of the stations of the study, yet with no welldefined spatial structure. In this case and at 50/0 level of significance, 44, 15, and 41 percentages of the stations possessed positive, negative, and without trend for the parameter under study, respectively. In general the behavior was different for different climates and no specific pattern was found. By the result, one may hypothesize that, in future, more regions will experience higher temperature values. Despite that some stations did not show significant trends, yet their positive trends may be a clue for future warming. This finding was verified through four recent years of 1999-2002. All of the stations showed higher average mean annual tel11perature, as was compared with average of corresponding to the common period of 1968-98.

Temperature, Climate, Time trend, Iran