In order to test the hypothesis of connection between the changes in climatic parameters and declining northern Zagros forests in the west of Iran, long-trends of meteorological parameters and reference evapotranspiration (ET₀) on seasonal and annual time scales using three synoptic meteorological stations of Piranshahr, Saghez, and Khoram-Abad were examined. The Penman-Monteith combination equation was applied to calculate the ET₀. To examine the long-term trends of meteorological parameters and ET₀, the non-parametric tests of Mann-Kendal and Spearman were used and the significance of the slope of trends lines was tested using the Sen-slope estimator. Results showed that the increasing trends of air temperature in Piranshahr (1986-2009) were statistically significant (P < 0.01). Wind speed exhibited a significant positive trend in Saghez (1970-2009) and Khoram-Abad (1970-2010) by Spearman test (Saghez at 0.05% level, Khoram-Abad at 0.01% level). On seasonal time scale, the trends of climatic parameters and ET₀were similar by Mann-Kendal and spearman tests and ET₀trends were positive in most stations. This preliminary research indicated that long-term trends of some climatic parameters and ET₀ in the northern Zagros region were statistically significant so that the hypothesis of the connection between decline of northern Zagros forests and changes in meteorological parameters was confirmed. Greater number of meteorological stations throughout the Zagros region, however, should be included in future research.