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1.3. Atmosphere and Climate 1.3.1. Wind The wind patterns of the Caspian are greatly affected by the Earth’s main air masses. There are cyclones in the southern and central parts of the sea with an immense general influence. The force of the wind is greater in the winter than in the summer throughout the region. In the Iranian coastal areas, there is a northwesterly prevailing wind known as the “Gilehva” as well as a group of winds originating in the northwest plains. Both of these currents can create storms along the Iranian shoreline. There is also a southern hot wind current known as the “Garmich” (hot wind) that usually blows in the winter and sometimes is very strong. In addition to these currents, there are local winds affected by the general dynamics of Earth-atmosphere interaction. Given the varying elevations of Golestan province, wind currents adhere to no systematic patterns. They are, however, usually affected by two factors. (1) Wind currents blow primarily along the high elevations and valleys near this area. (2) In the coastal areas, they generally blow vertical to the shoreline. The major wind currents are (A) Northeastern Wind that blows in spring, summer and autumn. In the first half of the year, it is considered an important wind and in the second half of the year heralds rainfall. (B) Caspian Wind originates from the north and northwest and is cold and stormy. (C) Southern Wind comes in from the Alborz Mountains to the plains in the fall and winter. A warm wind raises temperatures and is a factor in crating conditions for forest fires. Maximum wind speed in this province is 18 km per hour. The diversity and extent of wind currents in Mazandaran province is less than Gilan province, but the wind patterns in Gilan province prevails in this province as well. In the central and western parts of Mazandaran, there are two major currents. (1) Moist Western Winds, which are warm and usually cause rainfall. They do not blow in winter. (2) Eastern and the Northeasterly Winds that decrease the temperature and precipitate snowfall 1.3.2. Precipitation The Caspian coastal region more water resources than any other region in Iran. The close proximity of the Alborz Mountains to the Caspian Sea provides a unique climate with frequent snow and rainfall and hence a great concentration of water in this area. These waters are either absorbed by the underground layers and create a rich underground water source or join the rivers and streams and eventually enter the Caspian Sea. The Caspian shorelines have three types of rainfall. First, the rainfall created by the passing of humid Mediterranean, Red Sea and Sea of Oman fronts in the fall, winter and early spring. Second, the rainfall created by the Atlantic Ocean fronts in the spring and summer. This air front gains in humidity when it crosses the Caspian and causes rainfall in August and September. Third, the rainfall created by the humidity of the Caspian Sea itself as the result of cold air masses moving across the warm sea. The annual rainfall in the Caspian watershed basin is estimated as 437 mm. Based on the same statistics, 90% of the watershed basin area has more than 200 mm of rainfall and 10% enjoys over 800 mm of rainfall annually (Figure 4) Precipitation increases from east to west. The cities of Gorgan and Gonbad-e Kawus have an average rainfall of 400 to 500 mm annually in the east, and the cities of Rasht and Anzali have an average rainfall of 900 to 1000 mm annually in the west. However, the rainfall decreases as we move toward the city of Astara. Thus, the average annual rainfall of the western sections is 2-3 times the rainfall in the eastern sections (Figure 5). The maximum rainfall occurs at the south of Port Anzali with an average annual rainfall of 2,000 mm. The Caspian coastal regions are divided into five rainfall categories as it is shown in Figure 3. The maximum rainfall along the shoreline occurs in autumn and winter. Nevertheless, there is continuous rainfall throughout the year. Considering the scarcity and irregularity of rainfall in the rest of the country, we can conclude that the Caspian coastline has the most stable and predictable annual rainfall patterns in the country. The difference in the amount of rainfall in the eastern and western regions can be traced to the number of rivers in each section. Mazandaran province has the largest number of rivers, but the rivers in Gilan province supply the greatest volume of water to the Caspian Sea. The rivers in Gilan have the highest annual current and flow rates and the largest number of seasonal rivers in the northern region. Gilan Province has the highest rate of humidity because the Alborz Mountains in the south trap the humidity and create considerable rainfall throughout the year. But, the rate of precipitation is different in various parts of the province. For example, Port Anzali has the highest rate and Roudbar and Loushan (in the south) has the least amount of rainfall. The fluctuation for one year to another is mild and reveals the presence of a readily discernible system for the region. The average annual rainfall at the Gilan shoreline is 1,500 mm that increases from west to east. There are two distinct climates in the Mazandaran Province, namely plain and mountainous. The maximum annual rainfall in the mountainous region is 1,200 mm. 1.3.3. Insolation 1.3.4. Evaporation 1.3.5. Wave regime 1.3.6. Air temperatures The Caspian coastal region has distinct climatic divisions. The total area of this region is 108,584 Square Kilometers and contains three major sections: (1) Sefid-Roud, Talaab and Talesh (2) Coastal region (3) Gorgan and Dasht. This area covers 6.7% of the national coastal area. This region could be divided into two climatic basins. The first one is the Safid-Roud basin (except the coastal region) and the second includes the entire Caspian shoreline up to the water division line in the Alborz Mountains. The elevation difference in these two basins as well as the humidity of Caspian and non-Caspian regions has created a broad spectrum of climatic diversity in this area. In general, dry climates are not observed in this region and the M4 Type (warm type) is not evident. Other climates, however, are present. Table 1 provides the land distribution and areas affected by each climate. The table shows that the broadest climate in our study is the semi-dry climate. This accounts for the basic prevailing weather in the Sefid-Rood basin. The smallest climatic basin is the extremely dry, desert like weather, which only covers 1% of the region’s area. From the thermal climates or sub-climates perspective, the broadest climate belongs to the --- cold or elevated climates at 51%, cold climates 30% and moderate climates 19%. The main sources of rain and humidity in the northern region of Iran and the Caspian are the humid air masses coming from the Atlantic Ocean and Mediterranean Sea. The temperature changes in Gilan and Mazandaran Provinces (west and center) are slight. The average temperature in the hottest month of the year is 27° C and in the coldest month of the year is 25° C. Usually, the temperature never exceeds 37° C. The temperature reaches 44° C in the eastern region in cities like Gorgan. Generally, the eastern region has a dryer climate than the western sections. Mazandaran province features two opposite climates. One is characterized by the plains at the vicinity of the sea and the other the mountains in the elevated areas of the province. The plain climate has moderate weather while the mountainous climate brings cold weather, snow and frost. In general, the climate of Mazandaran is moderate and humid. The winds blowing from the west are warm and bring rainfall and the winds blowing from the east and northeast are cold and precipitate snowfall. The climate of Gilan province is also moderate and humid, but the extent of the temperature fluctuation is smaller and the humidity is higher than in Mazandaran. Golestan features a primarily moderate and humid climate similar to the Mediterranean. But given the closeness of its northern reaches to the Ghareh Ghom desert in Turkmenistan, it has dryer weather. The overall climate of this province is dryer than the other two provinces, but it has greater climate diversity with substantial natural resources and potentials. 1.3.7. Air pollution The main sources of air pollution along the Southern Caspian coastlines are industrial units, as well as transportation activities, using fossil fuels. The industrial activity is the most important source of air pollution. Existing plants, have not observed standards set by law, such as installation of the special filters to collect dust, soot and other polluting particles created by the combustion of different fuels, therefore they pollute the air through various emissions causing numerous environmental problems in the area. The industrial units are divided into three categories:
A. Mazandaran & Golestan Provinces The number of air polluting industrial units in these provinces exceeds 780 in 1996. Among these units, rice threshing factories (32% of total units) are the most polluting ones, and aluminum factories (0.1%) at the least polluting industrial units if this province. Transportation is also responsible for air pollution. Vehicles (petrol & gasoline consuming engines) emit pollutants such as: CO and Ox, and hydrocarbons (HC), suspended particles and sulfur oxides. There were 7,750 vehicles, out of which 6,812 used petrol and 938 used gasoline (diesel engine). A total of 176,415,000 liters of gasoline and 136,182,000 liters of petrol fuel were consumed in these provinces. The amount of annual consumption of fuel used by different industrial units is presented in Table 2. B. Gilan Province Different large factories are responsible for 33.3% of air pollution in Gilan Province, which cement factories are the most polluting units. They cause serious air pollution and threaten the health of the people. Iron units, asphalt making factories and shell crushing factories also contribute to the existing air pollution to a great extent. Rice threshing factories (1800 units) also add to the problem of air pollution. In Gilan Province, there were 150,000 vehicles on the road in 1996, which at least doubles during the New Year periods and summer holidays. Total daily fuel consumption based on the average of 15 liters per day for each vehicle is about 1,575,000 liters. This figure too, is doubled during holidays. It should be mentioned that continuous rainfall and wind currents throughout the year, reduces the observed air pollution and it is not as serious as the other major towns in the country. Although, they are usually washed away, unfortunately most of the pollutants find their final way into the sea. |
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