ABSTRACT:Decline of the Zagros forests of western Iran dominated by oak trees is assumed to be highly connected with changes in meteorological parameters. To examine this hypothesis, we aimed at observing the long-term trends of meteorological parameters and reference evapotranspiration (ET 0 ) in the Zagros region. Long-term (1961Long-term ( -2010 data of air temperature (T a ), relative humidity (RH), precipitation (P), and wind speed (WS) were obtained from meteorological stations located in the Zagros region. The Penman-Monteith equation was applied to calculate ET 0 . The results indicated that since 2000, coinciding with the emerging oak decline, meteorological parameters and ET 0 have been changed: T a +0.6°C, P -60 mm, RH -3%, WS +0.4 m·s -1 , and ET 0 +0.25 mm·day -1 . Although this research confirmed a significant relationship between oak decline and changes in meteorological parameters, full datasets recorded in different parts of the Zagros region are essential for a reasonable research to fully explain this hypothesis. Managers should think of the expected changes in meteorological parameters and evapotranspiration owing to global warming.