Human health and comfort, crop productivity, water resource availability, as well as the other critical hydrological, climatological, and ecological parameters are heavily influenced by trends in daily temperature maxima and minima (T_dmax, T_dmin, respectively). Using Mann-Kendall and sequential Mann-Kendall tests, trends in the number of days when T_dmax≥ 30°C or T_dmin ≤ 0°C, over the period of 1961 to 2010, were examined for 30 synoptic meteorological stations in Iran. For 67% of stations, days when T_dmin ≤ 0°C showed a significant negative trend, while only 40% of stations showed a significant positive trend in days when T_dmax≥ 30°C. The upward trend in T_dmax became significant between 1967 and 1975, according to the station, while the downward trend in T_dmin became significant between 1962 and 1974 for the same stations. Changes in precipitation type across most parts of the country show a high correlation with these temperature trends, especially with the negative trend in T_dmin. This suggests that future climatological and hydrological alterations within the country, along with the ensuing climatic issues (e.g., change in form of precipitation, drought, etc.) will require a great deal more attention.

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