Climate

Iran's climate is mostly arid or semiarid, to subtropical along the Caspian coast.

On the northern edge of the country (the Caspian coastal plain) winters are cold with heavy snowfall and subfreezing temperatures during December and January. Spring and autumn are relatively mild, while summers are dry and hot, but rarely exceed 29°C (84°F).

To the west, settlements in the Zagros Mountains basin experience lower temperatures, severe winters, sub-freezing average daily temperatures and heavy snowfall. The eastern and central basins are arid, with less than 20 cm of rain. Average summer temperatures exceed 38°C (100°F).

The coastal plains of the Persian Gulf and Gulf of Oman in southern Iran have mild winters, and very humid and hot summers. The annual precipitation ranges from 13-35 cm. 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.

Precipitation

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 centimetres or less. The major exceptions are the higher mountain valleys of the Zagros and the Caspian coastal plain, where precipitation averages at least 50 centimetres annually. In the western part of the Caspian, rainfall exceeds 100 centimetres annually and is distributed relatively evenly throughout the year. This contrasts with some basins of the Central Plateau that receive 10 centimetres or less of precipitation annually.