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weather
 Iran has a variable climate. In the northwest, winters are 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 °C (100 °F). 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 averages 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 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 is situated in Southwest Asia, bordering the Gulf of Oman, the Persian Gulf, and the Caspian Sea, between Iraq and Pakistan. Iran is one of the world's most mountainous countries. Its mountains have helped to shape both the political and the economic history of the country for several centuries. The mountains enclose several broad basins, or plateaus, on which major agricultural and urban settlements are located. Until the twentieth century, when major highways and railroads were constructed through the mountains to connect the population centers, these basins tended to be relatively isolated from one another. Typically, one major town dominated each basin, and there were complex economic relationships between the town and the hundreds of villages that surrounded it. In the higher elevations of the mountains rimming the basins, tribally organized groups practiced transhumance, moving with their herds of sheep and goats between traditionally established summer and winter pastures. There are no major river systems in the country, and historically transportation was by means of caravans that followed routes traversing gaps and passes in the mountains. The mountains also impeded easy access to the Persian Gulf and the Caspian Sea.
With an area of 1,648,000 square kilometers, Iran ranks sixteenth in size among the countries of the world. Iran is about one-fifth the size of the continental United States, or slightly larger than the combined area of the contiguous states of California, Arizona, Nevada, Oregon, Washington, and Idaho.
Located in southwestern Asia, Iran shares its northern borders with former Soviet Union republics Armenia, Azerbaijan, and Turkmenistan. These borders extend for more than 2,000 kilometers, including nearly 650 kilometers of water along the southern shore of the Caspian Sea. Iran's western borders are with Turkey in the north and Iraq in the south, terminating at the Shatt al Arab (which Iranians call the Arvand Rud). The Persian Gulf and Gulf of Oman littorals form the entire 1,770 kilometer southern border. To the east lie Afghanistan on the north and Pakistan on the south. Iran's diagonal distance from Azerbaijan in the northwest to Baluchestan va Sistan in the southeast is approximately 2,333 kilometers.
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