Based on temperature and precipitation characteristics and topography of the region, Mazandaran province can be divided into two types of Caspian temperate climate and mountainous climate. Its mountainous climate is on two types of temperate mountainous and cold mountainous.
1. Caspian temperate climate
This type of climate includes the western and central plains of the province to the northern foothills of Alborz. Due to the short distance between the mountains and the sea, moisture accumulates in these areas, which can result in significant rainfall and temperate temperatures. The average annual rainfall in the coastal strip of the province is 977 mm. Its spatial distribution from west to east is decreasing, while its temporal distribution is more or less regular (The maximum rainfall occurs in autumn and the minimum in spring)
In the study of temperature parameter, it is observed that due to high relative humidity and high number of cloudy days, temperate air temperature and temperature range is limited, which leads to hot and humid summers and mild winters with occasional frosts.
2-a) temperate mountainous climate
With the gradual increase of altitude from plain lands to the northern slopes of Alborz heights and distance from the sea, special changes in the climate of the province appear. In the altitude band of 1500 to 3000 meters, mountainous climatic conditions prevail, which can be characterized by a decrease in annual rainfall as well as a decrease in the average monthly temperature. In addition, cold winters with long frosts and short summers are other characteristics of this climate.
2-b) Cold mountainous climate:
At an altitude of more than 3,000 meters, which includes the peaks of the mountains on the northern slopes of the Alborz, the air temperature drops sharply and long frosts form. In these areas, precipitation is often in the form of snow, which accumulates in the long cold period of the year and lasts until the middle of the short warm period of the year. in these areas and at the top of Damavand Mountains, Alam Kooh and Takht-e Soleiman, conditions have been provided for the creation of mountain glaciers and permanent accumulation of snow.
Air masses affecting the climate of Mazandaran
The special geographical position of Mazandaran province as one of the coastal provinces of the Caspian Sea has caused it to benefit from the climatic effects of neighbors such as the vast land of Siberia, the Mediterranean Sea and the Caspian Sea and the central plateau of Iran throughout the year. During different seasons of the year, several air masses enter the province, which the most important are as follows:
A) Cold period of the year:
-Continental polar air mass (cP) that enters the province through the expansion of the Siberian high pressure system on the northeast of the country. This air mass that is cold and dry, absorbs moisture and heat by crossing the Caspian Sea, and so becomes unstable and causes significant rainfall, especially in autumn (due to the large difference between water temperature and air temperature) in the province. The intensity of this rainfall is more than other parts of the province due to the long path of air mass movement on the sea in the west of the province.
-Modified polar sea air mass (mP) originating in the Atlantic Ocean, which enters the eastern Mediterranean Sea through the Black Sea via the Black Sea and then enters Iran from the northwest via Turkey.
-Continental Arctic air mass (CA) of Scandinavian origin, which, after crossing Europe and losing moisture, regains moisture from the Black Sea and enters the northern strip of the country through Turkey.
b) Warm period of the year:
– Modified tropical sea air mass (mT) of Azores origin (Azores in the Atlantic Ocean) that enters the north of the country after crossing the Mediterranean Sea and southern Europe, and sometimes through North Africa and Saudi Arabia, southern regions and It attacks the center of Iran and penetrates to the north. The fronts of this air mass, when reaching the Caspian Sea, absorb moisture from this sea and cause rain on its southern coasts. In addition, At the peak of hot days, when the subtropical jet moves to the north of the Caspian Sea, the continental tropical air mass (CT), which is formed in central Iran and is very hot and dry, also affects the north of the country.
Climate of Mazandaran province
1 – According to Hansen classification, this province is located in a warm temperate circuit.
2 – According to the Temoenatenus Index method, this province is very temperate and super-temperate (The coefficient of moderation means to get the distance or proximity of a region to the temperate region)
3 – According to De Martounne classification, the western regions of Mazandaran are very humid, the central regions of Mazandaran are humid and the eastern regions of Mediterranean Mazandaran and the mountainous regions of Mazandaran are semi-humid.
4 – According to Dr. Karimi’s classification, the western and central regions have a humid climate with hot summers and slightly cold winters, the eastern semi-humid regions with warm summers and relatively cold winters, and the mountainous regions of Mazandaran have a humid climate with mild summers and very cold winters.