Climate change is a prevalent issue all around the world. Changes in the temperature and precipitation, as well as their distributions, are the evidence of climate change. Therefore, the objective of this study was to gather and standardize information about temperature (maximum and minimum temperatures and the discrepancy between them) and precipitation in Iran’s environmental zones. The long-term meteorological dataset was gathered from 47 synoptic stations for 66 years (1951–2017). Linear regression was employed to show the type and trend of changes in the studied variables. The Köppen method and UNESCO aridity index were adopted for climate classification based on temperature and precipitation criteria, respectively. Based on the Köppen method, the climate of Iran is defined into 4 environmental zones consisting of the arid desert (Bw), semi-arid (Bs), humid with mild winters (C), and humid with severe winters (D). On the basis of the UNESCO aridity index, the climate of Iran is classified into 5 environmental zones including very dry, dry, semi-dry, humid, and very humid. Results demonstrated that at 42 stations (89% of stations), the slope of the trend line was positive and long-term annual average temperatures of 5 stations (11% of stations) were negative. Furthermore, for precipitation, 11 stations (25% of stations) had positive trend and 33 stations had a negative trend (75% of stations). Finally, it was found that there are significant changes in both temperature and precipitation. On the other hand, an overall increasing trend in temperature and a decreasing trend in precipitation were observed from high-altitude or high-latitude cold areas to low-latitude regions such as costal lines in Iran.
