Why does Iran's northern Caspian coastal region receive much more rainfall than much of the country?

The northern Caspian coastal region of Iran receives significantly more rainfall than the rest of the country primarily due to the influence of the Alborz Mountains.

This mountain range acts as a physical barrier that seals off the narrow Caspian plain from the interior of the country. As northerly air movements, which are enriched with moisture from the Caspian Sea, move toward the coast, they collide with the steep faces of the Alborz Mountains. The mountains force this moist air upward, causing it to cool and wring out its moisture as precipitation.12

This process creates a distinct, humid climate on the Caspian slope, resulting in annual precipitation that can reach up to 78 inches (1,980 mm) in some areas, in sharp contrast to the arid conditions found across much of the Iranian plateau. This abundant rainfall supports a lush, semitropical environment characterized by luxuriant forests, swamps, and rice paddies.12