The heaviest concentrations are along the Caspian coast, in metropolitan Tehran, and in the provinces of East and West Azerbaijan. The environment has made land development difficult, time-consuming, and expensive. Iran consists of a rugged, mountainous rim surrounding a high, interior basin. The basin is composed of desert plains and two smaller mountain ranges. Iran's climate is characterized by wide variations in precipitation and temperature.
Seasonal changes are abrupt with a short fall and spring.
Prevailing winds produce adequate precipitation in the northwest and along the Caspian Sea but almost none in the eastern deserts and in the south. Most of Iran experiences long, hot, dry summers. Along the gulf and Caspian coasts, oppressively high humidity accompanies the heat. Winter temperatures are low in the north, while along the Caspian lowlands and the plain of Khuzistan, more equable conditions prevail. The major groups in this category include Persians, Kurds, Lurs, and Baluchi.