Iran's geography: a dry basin walled in by mountains

How mountains ring a dry interior plateau

Two ranges make the wall. The Zagros run north-west to south-east from the borders with Turkey and Iraq to the Strait of Hormuz, and in the south they widen into a band of parallel ridges about 200 kilometres across between the plains of Mesopotamia and the central plateau. Many Zagros peaks pass 3,000 metres, and the Geography of Iran article counts at least five above 4,000 metres in the south-centre; further south-east the summits fall below 1,500 metres. The Alborz are narrower and higher. They run along the southern shore of the Caspian Sea to meet the Kopet Dag and the ranges of Khorasan on the north-eastern border.

The highest point is Damavand, a volcanic cone in the middle of the Alborz, and its height is a measurement that has not settled. The country's record gives 5,628 metres, the Iran article on Wikipedia 5,610 metres and Britannica 5,671 metres, and Britannica notes that many of the country's peaks are poorly surveyed and their heights still disputed. The lowest point is the surface of the Caspian, 28 metres below sea level.

Inside the ring lies the Central Plateau, a set of closed basins averaging about 900 metres. Its eastern half holds two salt deserts, the Dasht-e Kavir and the Dasht-e Lut, which are uninhabited except for scattered oases. Where water collects in the lowest basins and evaporates it leaves salt flats, the kavirs that give the northern desert its name. Higher up, sand and gravel give way to fertile soil on the slopes, and that is where the towns are. Britannica describes the soils as a ladder of the same kind: rich brown forest soils on the Caspian side, shallow stony layers on the mountains, brown or chestnut soil carrying grass on the semi-arid plateaus above 900 metres, and light, salty, infertile ground in the driest basins, where dunes not held by plants move almost constantly in the wind.

Iran has two lowlands, and both sit outside the wall. The Khuzestan Plain in the south-west is a triangular extension of the Mesopotamian plain about 160 kilometres wide, much of it marsh, rising barely a few metres before it meets the first Zagros foothills. The Caspian plain in the north is longer and thinner: Britannica describes a strip 650 kilometres long and never more than 115 kilometres wide, falling from 3,000-metre summits to a shore below sea level. Along most of the Persian Gulf and the Gulf of Oman there is no real plain, because the Zagros come down to the water.

The record gives the total area as 1,648,195 square kilometres; the Geography of Iran article splits it into 1,531,595 of land and 116,600 of water. Britannica prints a smaller total, 1,630,848 square kilometres.

Where the rain falls and where it does not

Britannica describes a climate running from subtropical to subpolar, and the mountains decide which. In winter a high-pressure belt from Siberia pushes into the plateau, while low-pressure systems form over the Caspian, the Persian Gulf and the Mediterranean. The country's annual average is about 400 millimetres, and more than half of it falls in the three winter months. Outside the Caspian strip, summer is dry.

The north coast is the exception that the Alborz create. The range wrings the moisture out of air coming off the Caspian, and the plain below has forests, swamps and rice paddies, temperatures up to 38 °C, humidity near saturation and frost that rarely comes. The Geography of Iran article puts rainfall in the western Caspian above 1,500 millimetres a year, spread across all twelve months.

The interior and the south are the other extreme. Some basins of the Central Plateau receive 100 millimetres or less. Britannica gives Abadan, in Khuzestan, an average summer daytime temperature above 43 °C, while the average winter high in Tabriz in the north-west barely reaches freezing. Two winds work the east and south: the shamal, which blows from the north-west through the Tigris and Euphrates valley from February to October, and the "120-day" summer wind of Sistan near the Pakistani border, which can reach 110 kilometres an hour. In the north and west the year has four seasons; towards the south and east spring and autumn shrink until only a mild winter and a hot summer are left.

Why rivers in Iran rarely reach the sea

Rain that falls on the outer slopes runs down to the Caspian, the Gulf or the Gulf of Oman. Rain that falls inward stays inside: the streams flowing onto the plateau end in salt marshes and seasonal salt lakes, and most of them carry water only after the spring snowmelt. Britannica describes spring floods that do great damage and summer beds that run dry.

The Karun is the only navigable river. It rises in the Zagros and runs 830 kilometres to the Shatt al-Arab, known in Iran as the Arvand Rud, and shallow-draught boats use about 180 kilometres of it between Khorramshahr and Ahvaz. The Karkheh, 700 kilometres long, joins the Tigris. The Zayandeh, 300 kilometres long, supplies Isfahan and ends in the Gavkhuni marsh north-west of Yazd; since the Kuhrang Dam was finished in 1971, a tunnel 3 kilometres long has diverted water from the upper Karun into it.

Lake Urmia in the north-west is the largest body of water inside the country. Britannica gives its area as varying between about 5,200 and 6,000 square kilometres, and its brine is too salty for fish or most other aquatic life. A chain of connected salt lakes lies along the border with Afghanistan in Sistan and Baluchestan.

How qanats carried water under the desert

Where rivers fail, water has been taken from underground. UNESCO describes the qanat as a system that taps the alluvial aquifer at the head of a valley and carries the water by gravity through a tunnel, often for many kilometres, to fields and settlements on the dry plain. Eleven qanats were inscribed on the World Heritage List in 2016 as the Persian Qanat, together with the workers' rest areas, reservoirs and watermills built along them, and UNESCO notes that the communal system of sharing the water is still in use. The Persian Garden, inscribed in 2011, is built on the same water: nine gardens in nine provinces, each divided into four parts around channels that both irrigate and decorate.

The pattern of settlement follows the water. The Geography of Iran article describes a basin dominated by one town, with hundreds of villages bound to it, and herders in the surrounding uplands moving sheep and goats between summer and winter pastures. Until highways and railways crossed the mountains in the twentieth century, the basins were largely cut off from one another and goods moved by caravan through the passes. Britannica describes the same arrangement from the other side: most people live on the edges of the interior, and the interior itself is almost empty.

Water is now the constraint the rest of the country is measured against. The Iran article quotes the United Nations Resident Coordinator in Iran: "water scarcity poses the most severe human security challenge in Iran today." The World Bank's country overview, which covers the Iranian year to March 2026, lists growing water and energy shortages among the pressures disrupting economic activity. The Geography of Iran article gives the country's total renewable water resources as 137 cubic kilometres in 2011, and puts 92% of water withdrawals down to agriculture.

What the deserts and forests hold

The Dasht-e Lut in the south-east was inscribed as a natural World Heritage site in 2016. UNESCO describes strong winds between June and October that carry sediment and carve yardangs, long corrugated ridges, on a scale it calls colossal, alongside stony desert and dune fields. A land surface temperature of 70.7 °C was recorded there in 2005, according to the Iran article.

The opposite environment lies a few hundred kilometres north. The Hyrcanian Forests, inscribed in 2019 and extended in 2023, run along the Caspian shore in Iran and Azerbaijan. UNESCO dates these broad-leaved forests to 25 to 50 million years ago, records more than 3,200 species of vascular plants, 180 bird species and 58 mammal species in them, and notes trees 300 to 400 years old. Forest covers about 7% of the country by the Geography of Iran article's figure. Oak forest spreads across the west and centre, juniper on the limestone mountains of the north-east and wild pistachio in the east and south.

Wildlife follows the same split. Leopards, wolves and brown bears live in the Hyrcanian massif and the Persian leopard ranges through the Alborz and Zagros. The Asiatic cheetah, which is extinct elsewhere, survives only in central and north-eastern Iran. Asiatic lions and Caspian tigers were lost by the early twentieth century. National parks, protected areas and wildlife refuges are run by the Department of Environment.

Why the ground in Iran keeps moving

Iran sits mostly on the Iranian Plateau, with its south-west on the Arabian plate, and it is seismically active. The Iran article puts the average frequency of earthquakes of magnitude 7.0 or more at one every ten years. Britannica counts a dozen such earthquakes in the twentieth century that killed large numbers of people, among them the tremor of 1990 in the Qazvin and Zanjan area that killed as many as 50,000, and the earthquake of 2003 at Bam in Kerman province, which levelled the town, destroyed its historic fortress and killed more than 25,000.

The volcanoes are mostly quiet. Damavand has not erupted in historical times, nor have Sabalan, at 4,812 metres, and Sahand, at 3,710 metres, in the north-west. Taftan in the south-east, at 4,042 metres, still emits gas and mud at intervals. Britannica traces a volcanic belt about 1,900 kilometres long from the Azerbaijani border to Baluchistan, and a field of lava and ash running 320 kilometres from Jolfa to the Caspian.

Where borders and waters are contested

Britannica gives the whole boundary as 7,680 kilometres, about a third of it coast. The Geography of Iran article gives 5,894 kilometres of land border, 2,815 kilometres of coastline and a further 740 kilometres on the Caspian. Its longest land borders are with Iraq, at 1,599 kilometres, and Turkmenistan, at 1,148; the shortest, with Armenia, is 44 kilometres.

Several of these lines are disputed, and the site records each position as a position. Iran administers the islands of Abu Musa and the Greater and Lesser Tunbs near the Strait of Hormuz, and the United Arab Emirates claims them. There is no agreed maritime boundary with Iraq beyond the mouth of the Arvand Rud. Iran objects to Afghanistan limiting the flow of dammed tributaries of the Helmand River in years of drought. On the Caspian, Iran's stated position is that the sea's resources should be divided equally among the five states on its shore, a reading that Russia, Azerbaijan, Kazakhstan and Turkmenistan do not share.