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More than half of Iran's international border of 4,430 km (2,750 mi) is coastline, including 740 km (460 mi) along the Caspian Sea in the north and 1,700 km (1,100 mi) along the Persian Gulf and adjacent Gulf of Oman in the south. Both the Caspian Sea and the Persian Gulf have important ports and contain extensive underwater deposits of oil and natural gas. Iran's largest harbor, Bandar-e ‘Abbās, is located on the Strait of Hormuz, the narrow passage separating the Persian Gulf and the Gulf of Oman.
Although more than 10,000 plant species have been identified in Iran, the natural vegetation in most of the country has been uprooted and replaced by cultivated crops or pastures. Natural forests consisting of beech, oak, other deciduous trees, and conifers grow in parts of the Elburz Mountains. Some regions of higher elevation in the Zagros Mountains contain wooded areas consisting primarily of oak. Wild fruit trees, including almond, pear, pomegranate, and walnut, grow in both the Elburz and Zagros mountains. In the more arid central part of the country, wild pistachio and other drought-resistant trees grow in areas that have not been disturbed by human activity. Tamarisk and other salt-tolerant bushes grow along the margins of the Dasht-e Kavir. A wide variety of native mammals, reptiles, birds, and insects inhabit Iran. Many species of mammals—including wolves, foxes, bears, mountain goats, red mountain sheep, rabbits, and gerbils—continue to thrive. Others—including Caspian tigers, Caspian seals, desert onagers, three species of deer, gazelles, and lynx—are endangered despite the establishment of special wildlife refuge areas and other government programs initiated to protect them. Some 323 species of birds inhabit Iran; more than 200 species are migratory birds that spend part of the year in other countries.
Iran's extensive petroleum and natural gas deposits are located primarily in the southwestern province of Khūzestān and in the Persian Gulf. Iran also has one of the world's largest reserves of copper; deposits are located throughout the country, but the major lode lies in the central region between the cities of Yazd and Kermān. This region also serves as a center for the mining of bauxite, coal, iron ore, lead, and zinc. Additional coal mines operate throughout the Elburz Mountains; iron ore mines also exist near Zanjān in the northwest, near Mashhad in the northeast, and on Hormuz Island in the Strait of Hormuz. Iran also has valuable deposits of chromite, gold, manganese, silver, tin, and tungsten, as well as various gemstones, such as amber, agate, lapis lazuli, and turquoise. Although about one-third of Iran’s total land area is cultivable, only 9.8 percent is under cultivation. An additional 6 percent of the total land is used for pasture. Forested areas, found primarily in the Elburz Mountains and the higher elevations of the Zagros Mountains, have declined slightly in recent decades and account for 6.8 percent of the total land area.
Iran’s varied landscape produces several different climates. On the northern edge of the country, the Caspian coastal plain, with an average elevation at or below sea level, remains humid all year. Winter temperatures rarely fall below freezing, and maximum summer temperatures rarely exceed 29°C (85°F). Annual precipitation averages 650 mm (26 in) in the eastern part of the plain (Māzandarān Province) and more than 1,900 mm (75 in) in the western part (Gilān Province). At higher elevations to the west, settlements in the Zagros Mountain basins experience lower temperatures. These areas are subject to severe winters, with average daily temperatures below freezing, and warm summers, averaging 25°C (77°F) in the northwest and 33°C (91°F) in the central and southern Zagros. Annual precipitation, including snowfall, averages more than 280 mm (11 in) at higher elevations. Most precipitation falls between October and April. The central plateau region also experiences regional variations. In Tehrān, located at an elevation of 1,200 m (3,900 ft) on the northern edge of the plateau, the temperature averages 2°C (36°F) in January and 29°C (85°F) in July. The city receives an average of 230 mm (9 in) of precipitation annually. The arid basins of central and eastern Iran generally receive less than 200 mm (8 in) of precipitation per year. Yazd, for example, averages less than 70 mm (3 in) of precipitation. Its winters are cool, but temperatures almost never fall below freezing; summers are very hot, averaging 38°C (100°F) for most of July and August. The coastal plains along the Persian Gulf and the Gulf of Oman in southern Iran have mild winters, with average January temperatures ranging from 7° to 18°C (45° to 64°F) in Khūzestān Province; average temperatures are even higher in Bandar-e ‘Abbās on the Strait of Hormuz. Summers are very humid and hot, with temperatures exceeding 48°C (119°F) during July in the interior areas. Annual precipitation ranges from 145 mm to 355 mm (6 to 14 in) in this region.
Iran's rapid urbanization and industrialization have caused major environmental problems. Air pollution, primarily from automobile and factory emissions, has become a serious problem in Tehrān and other large cities. A rising incidence of respiratory illnesses prompted the city governments of Tehrān and Arāk, southwest of the capital, to institute air pollution control programs. These programs aim to reduce gradually the amount of harmful chemicals released into the atmosphere. Pollution of the Caspian Sea has increased substantially since the early 1990s, reaching levels that threaten sturgeon and other fish that sustain the Iranian fishing industry. Although Iran enforces stringent controls on the dumping of municipal and industrial wastes into Caspian waters within its territorial limits, the other countries that border the Caspian Sea do not control pollution in the northern two-thirds of the lake. Iran has urged these countries to sign a binding international agreement for cleaning up the Caspian Sea and preserving its water quality.
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