Physical Geography of Mesopotamia:
The Land Between The Rivers

"Mesopotamia" means "between the rivers", and that name is appropriate, as this land is defined by its rivers. The area is a rich alluvial basin that stretches between the high, hot deserts of the Arabian Shield in the west and south and the foothills of the Zagros and Kurdish mountains to the north and east. In the southeast, the rivers run into the Persian Gulf; in the northwest, a narrow strip of lowland connects Mesopotamia to the Mediterranean Sea by way of modern-day Syria. (Rzóska 1) The differing physical regions blend gradually into each other. The plateau of the Arabian Shield is only absolute desert east of Mesopotamia, in Arabia; the climate gradually becomes more gentle, becoming in much of Mesopotamia an arid steppe (Rzóska 5). In the northeast, the foothills of the Zagros Mountains fall into a piedmont region of gently rolling hills (Van de Mieroop, 38).

However, the region centers on two rivers: the Tigris and Euphrates. They originate in the eastern mountains, and are trapped in the Mesopotamian valley by the desert shield to the west. Both originate in the Turkish High Plateau, about 2000 m above sea level, and draw almost all of their water from outside the Mesopotamian region. The slope is steep in the early tributaries of the rivers, enabling them to pick up a lot of sediment. However, the land grows rapidly flatter, and they become slow, shallow, meandering rivers (Rzóska 41). The Euphrates flows around the north and west of the shorter Tigris, and they converge into the braided, swampy delta region in the south (Nemet-Nejat 11). Currently, the two rivers merge into the Shatt Al-Arab about 200 km from the Gulf; the Shatt is wide, narrow, and somewhat tidal (Rzóska 47). Other important rivers include the Khabur, the Greater and Lesser Zab, the Adheym and the Diyala, all major tributaries of the Tigris, they are supplied by snowmelt and rain in the Zagros (Rzóska 44). Because the Euphrates flows far to the west of the mountains for most of its length, it has no major tributaries. Several large rivers flowing from the mountains reach the Gulf in the same general area, though they are less important to the geography of Mesopotamia. The Karun carries water and sediments from the Iranian plateau, joining the Shatt Al-Arab sixty kilometers south of the junction of the Tigris and Euphrates, and the Kharkey, which was once a tributary of the Karun, peters out in the marshes to the north. There are no natural lakes in the region, but as the rivers slow down and widen out they often inundate large shallow areas, called 'haurs' in Arabic. The wider and larger of these are broad marshes and salt marshes, areas of flooded reeds threaded by narrow channels of clear water (Rzóska 47). Because of the geology and climate of the region, all of the waterways are constantly moving, flooding, and drastically altering their courses (Rzóska 44).

Mesopotamia, like most of the Middle East, has an extremely arid climate. Winter is the rainy season, with the more mountainous areas in the north getting around 400 mm of rain in the season from November to April, and little to none the rest of the season. South of the Euphrates, true desert conditions prevail, with much of the valley receiving less than 100 mm per year. Therefore the water the rivers bring down from the mountains is the major source of water for the valley. Rainfall is erratic as well, with variations of many hundred percent from year to year (Rzóska 2). This pattern of dry and wet seasons affects the waterways as well; water levels and discharges in the marshes and rivers vary along with rainfall. (Rzóska 50). The occasional unseasonal rainfall often produces flooding. The rainy season is the cold season as well, although the weather is never extremely cold; average temperature]s in January, the height of the wet cold season, rarely fall below freezing, averaging around 60º F(Rzóska 4). They hover around ninety in August, occasionally reaching as high as 120ºF. The flood periods of the rivers, the periods of maximum snowmelt and rain from the mountains, occur at the end of the rainy season, in April and June (Nemet-Nejat 10).

The geology of Mesopotamia underlies all the distinctive features of the area. The sandswept desert plateau of the Arabian Shield has been stable and undisturbed since the Cretaceous period, built on sandstones and limestones. The young mountains to the northeast consist of the same rocks, which were folded and twisted by continental forces during the Tertiary. Since their formation, they have been eroding, sending sediment to fill up the depression between the mountains and the desert (Rzóska 2). This process was greatly accelerated by the pluvial ages, the periods of heavy rainfall in the south that corresponded to the northern ice ages of the Pleistocene. It was during this period that most of the major rivers were formed in the mountains, as well as the wadis, dry or intermittent riverbeds that are a distinctive topological feature all over the Near East. The area that later became the alluvial plain has a much longer history; it began to submerge a hundred million years before the mountains formed, eventually flooding to form a shallow sea separating the Arabian and Iranian plateaus. During the period when this area was an intermittent seabed, layers of soluble limestone, salt, and gypsum were deposited. These deposits still underlie most of the Mesopotamian region (Rzóska 15). This is also the period when rich deposits of organic matter were formed; these deposits would later become oil, tar, asphalt and other such substances, which are plentiful enough in areas to natually seep to the surface. As world climate changed and the river began to carry large amounts of silt down from the new mountains, the former seabed filled with sediment, becoming a broad, fertile valley filled with rich brown soils. However, because of the underlying marine deposits, salinity often reduces the quality of the soil; rain or other water can bring buried salts to the surface through capillary action and solution in groundwater. This is counteracted primarily by the periodic floods, which rinse salts from the soil and deposit layers of new, uncontaminated soils (Rzóska 6).

Though the climate of Mesopotamia is classified as dry Mediterreanean, the extremes of terrain and distance from the sea mean that the major biome is midladitude grassland, steppe and prairie (Bergman 31). There are five major areas of vegetation in Mesopotamia. The desert-steppe area includes the southern and western regions, particularly most of the Euphrates valley.Vegetation in this area is either seasonal desert vegetation which grows for only a few weeks during the rainiest part of the year, or deep-rooted plants that can exploit the deep groundwater and handle the high salinity. (Rzóska 7). Along the banks of the rivers and streams, somewhat lusher vegetation is able to take advantage of the running water. Here the only trees are abundant date-palms (Van de Mieroop 67). Wild seed-bearing grasses such as varieties of emmer and barley are among the plants that grow on the steppe and the riverbanks (Nemat-Nejat 247). Herbs such as Astragalus, Salvia, and a variety of bulbs grow across the riverbanks and plains (Rzóska 10). Much of the alluvial plain is marshy and salty; palms again are commonplace. In the saltier, wetter areas, plants such as samphire, widget grass, phragmites, bulrushes, tamarix trees and more date palms, along with other marsh grasses, greens and shrubs, form a thriving, diverse ecosystem in the harsh environment (Chapman 222-223). The higher, hillier areas to the north grow gradually wetter and less salty. Vegetation is less dependent on the river systems. Poplars, willows, tamarisk, dates, pines and even scrubby oaks grow with some abundance, along with grasses and wild grains (Nemet-Nejat 12). Higher in the mountains, vegetation varies with altitude; true oak forests appear at middle heights, and the riversides are abundant with grasses, reeds, and trees such as willow, ash and plane. In the higher latitudes, the trees die off and the dominant vegetation is thornbushes like daphne, Crown-of-Thorns and others(Rzóska 9). The wide range of landscapes and environments in the small area produce an amazing biodiversity despite the harsh climate (Nemet-Nejat 12).

Animal species show equal diversity. Gazelle, deer, onager and wild sheep and goats browse (or once browsed) the grasslands (Nemat-Nejat 248). Wild ox, elephants, and rhinoceri may also have dwelled there at one time (Rzóska 17). Other mammals include a great many small burrowing rodents such and gerbils and mice; bats; hedgehogs, porcupines, and boar. Preying on this abundance are several species of big cats, wolves,hyaenas, mongoose, otters and marten. As recently as two centuries ago lions also roamed the area, and cheetah and tiger may have lived there in the past (Rzóska 12-13). A great many birds take advantage of the marshes, both year-round and as a vital resting place on the major European migration routes; more than 300 species have been observed passing through the marshes. Cranes, storks, and ducks populate the marhes in abundance (Rzóska 89). Reptiles such as [snake[s, geckos, and skinks, and a variety of amphibians, live in the rivers and deserts. Among the more notable of the many invertebrates are land snails, locusts, and mosquitos (Rzóska 13-14). Crabs, shrimp and aquatic invertebrates thrive as well (Rzóska 90). Fish live in the rivers (Rzóska 95-106).

The most ubiquitous fauna of the past ten thousand or so years, however, has been the human being. They adapted to the river-centered ecology and the wide variety of environments by developing cultures based on centralized, citified economies and irrigation agriculture, changing the landscape as much as the landscape changed them. Mud, the most common natural resource of an alluvial plain, formed their high temples, teeming streets, and majestic artworks. "The land between the rivers" becomes "the cradle of civilization."

Bergman E F. 1995. Human Geography. Englewood Cliffs, NJ: Prentice Hall.
Chapman, V. J. 1960. Salt Marshes and Salt Deserts of the World. New York: Interscience Publishers, Inc.
Nemet-Nejat, Karen Rhea. 1998. Daily Life in Ancient Mesopotamia. Westport, CT: Greenwood Press.
Rzóska, Jean. 1980. Euphrates and Tigris, Mesopotamian ecology and destiny. Monographiae Biologicae. Boston: Dr. W. Junk Bv Publishers.
Van de Mieroop, Mark. 1997. The Ancient Mesopotamian City. Oxford: Clarendon Press.

originally a geography 362 midterm