B. Ghahraman - Department of Irrigation, College of Agriculture, Ferdowsi University, Mashhad, Islamic Republic of Iran.
S. Taghvaeian - Department of Irrigation, College of Agriculture, Ferdowsi University, Mashhad, Islamic Republic of Iran.

This paper presents an analysis of annual precipitation trends in Iran. Mean annual rainfalls were collected from ۳۰ synoptic stations with a reasonable geographic distribu-tion and with data equal to or less than ۵۰ years. Trend analysis was investigated using a "regression line slope" method (annual rainfall as a dependent variable and year as an independent variable). The results showed that for the entire period, and at a ۹۵% level of significance, seven stations showed a negative trend, while a positive trend was found at six stations. The same data over the period of last ۴۰ years demonstrated that four and ۸ stations had negative and positive trends, respectively. Decreasing the record length, up to the last ۳۰ years, resulted in fewer stations with any significant trend. The results identi-fied that, in any case, the trend did not depend on the mean annual rainfall but rather re-cord length could have some effects on it.

IRAN, Annual rainfall, Record length, Regression line slope, Trend analysis