Iran has a diverse 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.
Rugged, mountainous rim; high, central basin with deserts, mountains; small, discontinuous plains along both coasts. The highest point is Mount Damavand (5,671 meters). Desert: Two great deserts extend over much of central Iran: the Dasht-e Lut is covered largely with sand and rocks, and the Dasht-e Kavir is covered mainly with salt. Both deserts are inhospitable and virtually uninhabited. Mountain: The Zagros range stretches from the border with the Republic of Armenia in the north-west to the Persian Gulf, and then eastward into Baluchistan. Zagros is extremely hard, difficult to access, and populated largely by pastoral nomads. The Alborz mountain range, narrower than the Zagros, runs along the southern shore of the Caspian to meet the border ranges of Khorasan to the east. Forest: Approximately 11 percents of Iran is forested, most extensively in the Caspian region. Here one finds the broad-leafed, vigorous deciduous trees, usually oak, beech, linden, elm, walnut, ash, and hornbeam, as well as a few broad-leafed evergreens. Thorny shrubs and fern also abound.The narrow Caspian coastal plain, in contrast, is covered with rich brown forest soil.