Most geographers discuss the country's geography in terms of four main zones or regions: the desert in the west and southwest; the rolling upland between the upper Tigris and Euphrates rivers (in Arabic the Dijlis and Furat, respectively); the highlands in the north and northeast; and the alluvial plain through which the Tigris and Euphrates flow.

The desert zone, an area lying west and southwest of the Euphrates River, is a part of the Syrian Desert, which covers sections of Syria, Jordan, and Saudi Arabia. The region, sparsely inhabited by pastoral nomads, consists of a wide, stony plain interspersed with rare sandy stretches. A widely ramified pattern of wadis--watercourses that are dry most of the year--runs from the border to the Euphrates. Some Wadis are over 400 kilometers long and carry brief but torrential floods during the winter rains.

The uplands region, between the Tigris north of Samarra and the Euphrates north of Hit, is known as Al Jazirah (the island) and is part of a larger area that extends westward into Syria between the two rivers and into Turkey. Water in the area flows in deeply cut valleys, and irrigation is much more difficult than it is in the lower plain. Much of this zone may be classified as desert.

The northeastern highlands begin just south of a line drawn from Mosul to Kirkuk and extend to the borders with Turkey and Iran. High ground, separated by broad, undulating steppes, gives way to mountains ranging from 1,000 to nearly 4,000 meters near the Iranian and Turkish borders. Except for a few valleys, the mountain area proper is suitable only for grazing in the foothills and steppes; adequate soil and rainfall, however, make cultivation possible. Here, too, are the great oil fields near Mosul and Kirkuk. The northeast is the homeland of most Iraqi Kurds.

The alluvial plain begins north of Baghdad and extends to the Persian Gulf. Here the Tigris and Euphrates rivers lie above the level of the plain in many places, and the whole area is a delta interlaced by the channels of the two rivers and by irrigation canals. Intermittent lakes, fed by the rivers in flood, also characterize southeastern Iraq. A fairly large area (15,000 square kilometers) just above the confluence of the two rivers at Al Qurnah and extending east of the Tigris beyond the Iranian border is marshland, known as Hawr al Hammar, the result of centuries of flooding and inadequate drainage. Much of it is permanent marsh, but some parts dry out in early winter, and other parts become marshland only in years of great flood.

Because the waters of the Tigris and Euphrates above their confluence are heavily silt laden, irrigation and fairly frequent flooding deposit large quantities of silty loam in much of the delta area. Windborne silt contributes to the total deposit of sediments. It has been estimated that the delta plains are built up at the rate of nearly twenty centimeters in a century. In some areas, major floods lead to the deposit in temporary lakes of as much as thirty centimeters of mud.

The Tigris and Euphrates also carry large quantities of salts. These, too, are spread on the land by sometimes excessive irrigation and flooding. A high water table and poor surface and subsurface drainage tend to concentrate the salts near the surface of the soil. In general, the salinity of the soil increases from Baghdad south to the Persian Gulf and severely limits productivity in the region south of Al Amarah. The salinity is reflected in the large lake in central Iraq, southwest of Baghdad, known as Bahr al Milh (Sea of Salt). There are two other major lakes in the country to the north of Bahr al Milh: Buhayrat ath Tharthar and Buhayrat al Habbaniyah.

The Euphrates originates in Turkey, is augmented by the Nahr (river) al Khabur in Syria, and enters Iraq in the northwest. Here it is fed only by the wadis of the western desert during the winter rains. It then winds through a gorge, which varies from two to sixteen kilometers in width, until it flows out on the plain at Ar Ramadi. Beyond there the Euphrates continues to the Hindiyah Barrage, which was constructed in 1914 to divert the river into the Hindiyah Channel; the present day Shatt al Hillah had been the main channel of the Euphrates before 1914. Below Al Kifl, the river follows two channels to As Samawah, where it reappears as a single channel to join the Tigris at Al Qurnah.

The Tigris also rises in Turkey but is significantly augmented by several rivers in Iraq, the most important of which are the Khabur, the Great Zab, the Little Zab, and the Uzaym, all of which join the Tigris above Baghdad, and the Diyala, which joins it about thirty-six kilometers below the city. At the Kut Barrage much of the water is diverted into the Shatt al Gharraf, which was once the main channel of the Tigris. Water from the Tigris thus enters the Euphrates through the Shatt al Gharraf well above the confluence of the two main channels at Al Qurnah.

Both the Tigris and the Euphrates break into a number of channels in the marshland area, and the flow of the rivers is substantially reduced by the time they come together at Al Qurnah. Moreover, the swamps act as silt traps, and the Shatt al Arab is relatively silt free as it flows south. Below Basra, however, the Karun River enters the Shatt al Arab from Iran, carrying large quantities of silt that present a continuous dredging problem in maintaining a channel for ocean-going vessels to reach the port at Basra. This problem had been superseded by a greater obstacle to river traffic, however, namely the presence of several sunken hulks that had been rusting in the Shatt al Arab since early in the war.

The waters of the Tigris and Euphrates are essential to the life of the country, but they may also threaten it. The rivers are at their lowest level in September and October and at flood in March, April, and May when they may carry forty times as much water as at low mark. Moreover, one season's flood may be ten or more times as great as that in another year. In 1954, for example, Baghdad was seriously threatened, and dikes protecting it were nearly topped by the flooding Tigris. Since Syria built a dam on the Euphrates, the flow of water has been considerably diminished and flooding was no longer a problem in the mid-1980s. In 1988 Turkey was also constructing a dam on the Euphrates that would further restrict the water flow.

Until the mid-twentieth century, most efforts to control the waters were primarily concerned with irrigation. Some attention was given to problems of flood control and drainage before the revolution of July 14, 1958, but development plans in the 1960s and 1970s were increasingly devoted to these matters, as well as to irrigation projects on the upper reaches of the Tigris and Euphrates and the tributaries of the Tigris in the northeast. During the war, government officials stressed to foreign visitors that, with the conclusion of a peace settlement, problems of irrigation and flooding would receive top priority from the government.