Iran's climate ranges from arid or semiarid, to subtropical along the Caspian coast and the northern forests. On the northern edge of the country (the Caspian coastal plain) temperatures rarely fall below freezing and the area remains humid for the rest of the year. Summer temperatures rarely exceed 29 °C (84.2 °F). Annual precipitation is 680 mm (26.8 in) in the eastern part of the plain and more than 1,700 mm (66.9 in) in the western part.
To the west, settlements in the Zagros basin experience lower temperatures, severe winters with below zero average daily temperatures and heavy snowfall. The eastern and central basins are arid, with less than 200 mm (7.9 in) of rain, and have occasional deserts. Average summer temperatures exceed 38 °C (100.4 °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 135 to 355 mm (5.3 to 14.0 in).
The Country Iran with 1648195 kilometers square areas is located in southern part of north moderate zone between 25 03′ and 39 47′ of northern latitude from equator circle and 44 14′ and 63 20′ eastern longitude from Greenwich meridian. Nearly 90 percent of Iran territory is situated in Iran Plateau district. Generally Iran is mountainous and semidry land, which its mean altitude is more than 1200 meters above sea level. More than one half of Iran consists of mountains, one quarter is plains and deserts and less than one quarter is farming lands. Lut Desert with 56 meters altitude is the lowest internal point and Damavand Summit in central Alborz Mountains with 5628 meters altitude is the highest point of Iran. In southern coast of Caspian Sea, the altitude of the ground is 28 meters lower than sea level.
From morphological and topographical approach, Iran is a relatively high plateau, which is located in middle part of Alpine-Himalayan fold belt. The huge ranges of Alpine-Himalayan fold belt that is continued from Europe to middle Asia are divided in two branches, Alborz and Zagros Mountains in Iran.
Southern branch, Zagros Mountains as a big wall separate central Iran from Mesopotamia plain. This range at southeast as a dam covers all coast of Persian Gulf and by connecting with Makran zone continue toward Pakistan.
Northern branch, Alborz Mountain, at north, is the boundary between interior land and Caspian Sea and after joint with NW-SE trending Kopeh Dagh range, separates Central Iran from Karakorum and Karazm deserts. Some parts of high elevation mountains of east Iran with NS trend are located between Lut block at west and Helmand block at east. These mountains are limited at south and north by Khab Playa and Makran Range respectively and complete the boundary of central Iran.
The third belt between Zagros and Alborz with NW-SE trend is situated in interior part of plateau-like central zone. This feature in contact with central Iranian blocks, make up some trough and lakes which, present current morphology of internal plains.
In the scale of general atmospheric currents, most of Iran territory correlates with air subsidence regions and because of this, in an uniform distribution pattern of climate, Iran is situated in the desert belt of northern hemisphere. However Iran has climatological diversity with three types of climate.
- Dry and semidry climate: large part of internal lands and southern border of Iran have this climate. The specifications of these regions are long dry periods that sometimes involve 7 months of the year. Also annual rain of the regions is among 25-30 millimeters.
- Mountainous climate which itself is subdivided to two categories, cold mountainous climate and moderate mountainous climate.
- Cold mountainous climate which dominants in 40000 km square areas of Iran has more than 500 millimeters annual rain.
- Moderate mountainous climate: with 250-600 millimeters annual rain, it dominants in 300000 km square areas of Iran.
- Caspianic climate: a narrow and small area between Caspian Sea and Alborz Mountain Belt with 600-2000 millimeters annual rain.
Figure 2: mead rain map of Iran Figure 3: climatological map of Iran, diversity in climates of Iran is as the result of extension in geographical latitude, long mountain belts, altitude remarkable variation and the position of country relative to seas and oceans.
Land and marine ecosystems, biodiversity, rivers and seas, swamps and grasslands are the main elements of natural environment and so every play its role in providing sustainable biological conditions. However the most part of Iran with low mean annual rain, are desert and semidry lands of high central plateau and threats against the environment are serious. But Iran from biodiversity approach has a good situation and we can find samples of rich biological resources. From viewpoint of numbers of plant genus, Iran is one of the richest floras of the world and swamps of the country are considered as important environmental resources.