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Further Reading

Climate

Iran has been described as having a variable climate. In the northwest, winters are traditionally cold with heavy snowfall and subfreezing temperatures during December and January. Spring and fall are relatively mild, while summers are dry and hot. In the south, winters are mild and the summers are very hot, having average daily temperatures in July exceeding 38^o C. On the Khuzestan plain, summer heat is accompanied by high humidity.

In general, Iran has an arid climate, in which most of the relatively scant annual precipitation falls from October through April. In most of the country, yearly precipitation historically averaged 25 centimeters or less. The major exceptions are the higher mountain valleys of the Zagros and the Caspian coastal plain, where precipitation averages at least 50 centimeters annually. In the western part of the Caspian, rainfall often exceeds 100 centimeters annually and is distributed relatively evenly throughout the year. This contrasts with some basins of the Central Plateau that receive ten centimeters or less of precipitation annually.

Iran's post-Revolution moves toward industrial development and its continued expansion of its oil industries were potential factors in future changes to its climate. By 2008 Iran reportedly suffered from air pollution, especially in urban areas, from vehicle emissions, refinery operations, and industrial effluents, deforestation, overgrazing, desertification, oil pollution in the Persian Gulf, wetland losses from drought, soil degradation (salination), inadequate supplies of potable water, water pollution from raw sewage and industrial waste, and other effects of urbanization.

Especially in urban areas, vehicle emissions, refinery operations, and industrial effluents contributed to poor air quality. Between 1985 and 2005, huge increases in energy consumption tripled carbon emissions. Most cars used leaded gas and lacked emissions control equipment. Tehran was rated by 2008 as one of the world's most polluted cities. The abundance of fossil fuels discouraged the use of alternative fuels. Much of Iran's territory suffers from desertification and/or deforestation. Industrial and urban wastewater runoff has contaminated rivers and coastal waters and threatened drinking water supplies. Wetlands and bodies of freshwater were increasingly being destroyed as industry and agriculture expanded, and oil and chemical spills had harmed aquatic life in the Persian Gulf and the Caspian Sea. Iran contended that the international rush to develop oil and gas reserves in the Caspian Sea presented that region with a new set of environmental threats. Although a Department of Environment had existed since 1971, Iran had not developed a policy of sustainable development because short-term economic goals, particularly support of the oil and gas industries, had taken precedence.