Due to its topography Iran has a temperate climate in general, although it is very cold or hot in some areas. Without its mountains, Iran would have been an arid country with wide deserts. There are four seasons in most parts of the country, with the exception of southern Iran, where hot summers and mild winters are characteristic for this area. Iran is affected by four air masses in different seasons. Wet and cold from north-west, wet and warm from south-west, dry and cold from north-east and dry and warm from south-east. But generally the penetrating Mediterranean air masses from west and north-west have a significant effect on more than half of the country. The average annual precipitation is between 500–800 mm. The majority of precipitation happens in Rasht (Gilan Province) and Kouhrang (Chaharmahal and Bakhtiyari province) (more than 2000 mm annually). On the other hand the average annual precipitation in central deserts reaches only to about 15 mm.
Heavy snowfall happens mostly in winter and the beginning of spring in high altitudes and in the northern areas. There is permanent snow on the mountains higher than 3800m and in summer the temperature of this zone does not go higher than 12 C and it remains frozen during most of the year. So the season for butterfly activity begins very late here (around July) and ends very soon (around the end of August). There is a great difference between highest and lowest temperatures in the country. In the summer the temperature in some areas in souh-west Iran reaches to +50 C, whereas it decreases to -30C in winter in other areas like Shahre-Kord in Central Zagros.