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Volume 18, Number 4July/August 1967

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Dry—But Why?

Written by Daniel Da Cruz
Photographed by T. F. Walters
Additional photographs by Khalil Abou El Nasr

Across the desks of government officials in Saudi Arabia about six years ago went a long dull report with a long dull title. It was called "A Study of the Wasia Acquifer in Eastern Saudi Arabia." Written by the Arabian American Oil Company (Aramco) after a year's study, it contained 115 pages of text, seven maps, six tables and one graph—hardly the kind of thing to bring readers to their feet. Yet in the slow, careful language of the report was buried some electrifying information: that under the hot desert sands of Saudi Arabia oozed enough groundwater to meet, and even exceed, the entire country's needs for years to come. To one of the driest countries on earth this was not merely good news; it was almost a miracle. For in Saudi Arabia, as in all the arid and desiccated regions of the Middle East, water is life itself.

Water is among the most ubiquitous of the earth's substances. It not only pervades the atmosphere as clouds and invisible vapor, but as open seas blankets 139,700,000 square miles of the terrestrial surface—nearly 40 times the area of the 50 United States—not counting the world's countless rivers, glaciers, lakes, bogs, swamps and swimming pools. Surrounded by so much water, it is surprising that any part of the solid, habitable 29 per cent of the earth's surface ever dries out, let alone becomes sterile desert.

Nevertheless deserts abound. In fact they constitute nearly one-third of the earth's land area, ranging from the rolling steppes of Central Asia and mountain valleys in Baluchistan to dry lake bottoms in Central Australia, flat deltas at the mouth of the Colorado River and even the sand-duned stereotype of popular fancy—which is in fact so uncommon that even the Sahara is less than 10 per cent dune sand. Even the sandiest desert of all, the Rub' al-Khali, or Empty Quarter, spreading across nearly one million square miles of the Arabian Peninsula, is only one-third dunes. In total area, it ranks third in size after the Sahara Desert, three times as large, and the Australian Desert, one-third larger.

Although it is quite possible to freeze in the desert—especially at high latitudes—deserts in the Torrid-Temperate Zone are every bit as hot as the fevered imaginations of movie-makers conceive them. The highest shade temperature ever recorded, 137°F, was registered at the desert settlement of Aziza in the Libyan Sahara. But since deserts seldom afford shade, this figure is less meaningful than typical summer surface temperatures, which during daylight hours can range from 150° to 170°F and up. At these brain-baking temperatures, usually accompanied by steady, desiccating winds, a normal adult needs nearly seven quarts of water a day merely to survive, never mind move.

Yet it is the extremes of heat and cold, rather than simply heat alone, which make desert climates so merciless, and curiously enough this usually results, in inland deserts at least, from an absence of the kind of atmospheric humidity which makes Philadelphia summers, for example, so soggily insupportable. Every day the sun pours down on the earth 50,000 times as much heat energy as man simultaneously consumes in all energy forms. Deserts absorb 90 per cent of the insolation falling upon them, while dust particles reflect skyward what's left. In humid climates like that of Philadelphia, on the other hand, the terrain absorbs only 40 per cent of the solar heat, 20 per cent being reflected upward by clouds, 10 per cent by dust, and 30 per cent by water areas and land cover such as forests.

At night the process is reversed. The same clouds, dust and land cover that in temperate climates attenuate the intensity of the sun's rays now trap 50 per cent of the residual heat, while in the desert the setting sun signals the dissipation of nearly all its accumulated daytime warmth. Thus the dry air which makes desert heat relatively bearable also accounts for the dramatic drop in temperature at sunset, when swings of 50°F are not uncommon and of 80° not impossible.

Latitude and altitude likewise condition desert climates. As a rule of thumb, 1,000 feet of altitude corresponds to a distance of 300 miles from the equator, so that the low-lying, equatorial Sahara is the world's hottest desert, while the Gobi Desert of the Mongolian highlands above the 40th parallel is the coldest.

Though deserts radiate an air of eternity to match their immensity, they actually seem to be geological newcomers compared, say, to the earth itself or to rain forests, but why this is, is very much a mystery since conditions that breed them have been around a long time.

One condition is the location of land masses and mountains in relation to oceans. Another is the presence or absence of clouds since, theoretically, land unprotected by the insulation of clouds quickly becomes a lifeless wasteland. Yet clouds alone do not guarantee that the land below will be green and productive. (To the contrary, climatologists estimate that 95 to 99 per cent of all clouds fail to produce precipitation.) Thus other forces must also be considered—such as the earth's diurnal rotation. These forces create and control the major wind belts that, in turn, are responsible for low pressure areas and high pressure areas. Low pressure areas—among them the equatorial rain forests and the misty plains of north central Europe—are wet because as air is pulled in to fill the relative vacuum in such an area, it rises in the steady updraft generated by the low pressure, cools as it leaves the earth's warm surface, until, finally, the moisture in it condenses and falls as rain or snow. At about 30° latitude, either north or south of the equator, the process is reversed, as air descends from the atmospheric heights—which is why most of the world's great deserts occur in these latitudes. Warmed by contact with the earth, the air picks up whatever moisture is present as it sweeps along the earth's surface toward a low pressure area, seeking to equilibrate the ever-changing pressure—and never quite succeeding. Where ascending, cooling air masses are absent, rain rarely occurs—a feature not only of the deserts but of the high-pressure polar areas, equally innocent of precipitation and vegetation.

Weather, of course, is not nearly as predictable as this neat pattern suggests since it is disturbed by the asymmetry of the continental land masses, seasonal temperature variations, the precession of the equinoxes, sunspots, volcanic action and even such man-made factors as forest fires and automobile exhaust fumes.

The oceans, which ultimately supply most water for precipitation, also upset the precarious balance of atmospheric pressures. Cold polar waters are impelled by centrifugal action toward the equator. But as the sun-heated surface layers evaporate, the deep ocean currents surge upward, and winds blowing landward across these frigid waters cool and lose their capacity to carry moisture. At times fog and mist drift tantalizingly ashore from such waters, onto the Patagonian Desert, Africa's Kalahari and other coastal wastes, but the sun burns them off before the parched sands can drink. In the deep interior of Asia, by contrast, warm water-laden air from the Pacific has been wrung so dry by its long overland passage that seldom is a drop left for the arid Gobi. In somewhat the same manner, ocean-born rain clouds rising to pass over mountain ranges are cooled and drained of their moisture within sight of the dry interior. It is thus that the wettest and driest spots on earth—the windward and leeward slopes of mountain ranges bordering the sea—are often separated by an interval the naked eye can span.

Of all fates, death by drowning on the desert seems least likely. Yet it is a far from rare phenomenon, owing to the fact that the less rain that falls on a given area, the more variable will be its periodicity, duration and quantity. But when rain does come, it often falls with demonic violence, torrentially, overtaxing the capacity of the soil to absorb it. It runs off in sheets from the slightest slopes, gathers volume and force in dry river beds, and roars through bone-dry canyons as tremendous flash floods which sweep them clean, often of people who hadn't suspected that somewhere, miles away, rain had fallen only minutes earlier. Once in the Mojave Desert a flash flood, becoming a moving wall of mud when it dissolved alluvial sediment in its path, carried a locomotive a mile from the right-of-way before completely burying it. Typically, a few days after such a cloudburst, it is almost impossible to tell when it rained last—a week or five years before.

A desert is nature's Sleeping Beauty, needing only the gentle caress of raindrops and the right temperatures for it to spring to vibrant life. But nature is capricious with its water, flooding Hawaii's Mt. Waialeale with an average 471 inches of rain a year, while parsimoniously denying many of the temperate lands the minimum 10 inches of water they need annually to sustain crop growth. None is so ill-favored as Chile's Atacama Desert, which has now endured 375 years without a drop of rain, although years often intervene between rains in deserts such as Saudi Arabia's barren Rub' al-Khali.

Yet nature finds a way of surmounting her self-inflicted handicaps, and in the desert plant kingdom some of the solutions are marvels of adaptation. Perennials abound and by a conservative metabolism often manage to see the next rain. Some annuals are so specialized that a downpour will cause their seeds to germinate, send down roots, grow to maturity, bloom and cast their tough seed on the ground—all within a period of weeks, after which the seed may lie unaffected for years until the next rain comes. Some seeds even have a soluble coating that dissolves to initiate germination only when enough rain has washed over it to guarantee that it will be able to complete its life cycle. Cactus plants store their water in cells and ration it out slowly over long periods of drought, while deciduous plants shed their leaves during dry spells to limit evaporation.

That so much of the world's lands are green only with such hardy but unlovely vegetation as cactus, is a misfortune for which man can partly thank himself. During the past 3,000 years, mankind has often proven more destructive than the elements to his rich terrigenous heritage. Abandonment of Roman territorial farmlands as the Empire dissolved, wanton destruction of oases by nomadic invaders, overcropping of pasturage by the cattle and horses of the same roving armed bands—all were factors in the progressive denudation of old world crop land. Exposed to the erosive forces of wind and water, stripped by ruminants of the grass roots which held it together, the thin top soil was blown away or washed into the sea.

Ironically, it was in Mesopotamia, the fertile valley between the Tigris and Euphrates, that the first man-made desert was created, in the same place that civilization was born. Over the millennia man's plow bit into the land and produced bountiful crops, while his newly domesticated animals grazed nearby, and the surplus food allowed the beginning of villages and the division of labor upon which urban culture was erected. It also allowed standing armies, and when in medieval times the Mongols under Hulagu Khan overran the Fertile Crescent, they destroyed not only those armies but the corps of engineers which maintained the irrigation system on which Mesopotamia's agriculture was based. Soon the irrigation and drainage canals silted up, corrosive salts whitened the land like snow and plowing fed dry topsoil to the wind. Where grass tenaciously managed to survive, sheep and goats tore it from the soil, roots and all. In a generation Mesopotamia was an almost abandoned wasteland well on its way to becoming a desert.

The process goes on today despite modern man's knowledge of methods needed to arrest, or reverse, the encroachment of the desert. The Indus Valley, for example, has more than sufficient water, yet has a delta of infertile clay. And in some places loss of land due to waterlogging and salanity is outracing the gain through traditional land reclamation techniques—suggesting, perhaps, that more than water is required to transform the desert into productive agricultural land and maintain the shaky balance of natural forces which it represents.

In Saudi Arabia, for example, the fact that vast amounts of water trickle through the earth thousands of feet below is by no means news to hydrologists. Ever since 1939 when Aramco's experts began to chart the underground deposits they were finding during the search for oil, they have suspected that the totals would be enormous. But to countries without widespread and relatively sophisticated networks of mains and pumps to carry it to the farms and cities where it is needed, the mere presence of water isn't enough. Despite the discoveries at Wasia for instance, Saudi Arabia began to build a seawater de-salting plant on the Red Sea coast last February because there is no way yet to get the Wasia water to Jiddah.

Another problem is that the Bedouins who, government agencies hope, will create and maintain new agricultural land, have so far shown little enthusiasm toward exchanging their nomadic independence for the security permanent settlement offers them as a landowner; they feel that the whole land—not just a single plot—is theirs anyway.

Those factors, of course, count for little in the face of the benefits inherent in the Wasia findings. Estimating the Saudi Arabian population at 5,000,000, the productive land required at two acres per capita and the irrigation demand at 110 barrels per acre, statisticians have arrived at a maximum requirement of approximately one billion barrels per day—and in the Wasia acquifer alone there are reserves of 200 trillion barrels, enough, at present rates of consumption, to serve the whole united States for more than 60 years.

In addition to Wasia there are such sources as Turabah where in late 1966 fresh water gushed to the surface from a depth of 7,400 feet (possibly the second deepest water well in the world) at a rate of 500 gallons per minute. And Wasia and Turabah are but two of dozens of similar acquifers.

For a desert country these are enormous amounts of water—enough, say some, to change the entire face of the country. First, of course, Saudi Arabia must construct the wells, mains and canals essential to effective distribution and use. The country must also find or train enough farmers to tend the fertile, verdant farmland that this water will create. These are not projects that are completed overnight; they will take time, patience and work. But now, with virtually limitless reserves of water to tap, the formerly insuperable barriers to agricultural progress and industrial development have been breached. In Riyadh, for example, Swedish, French, Saudi and Finnish firms are already designing and installing a system to lift, purify, cool, deliver and store up to 10,000 gallons a minute, most from the Wasia acquifer. For a country that has always been dry but never known why, the answer is at hand at last.

Daniel da Cruz is Middle East correspondent for McGraw-Hill World News.

This article appeared on pages 6-9 of the July/August 1967 print edition of Saudi Aramco World.


Check the Public Affairs Digital Image Archive for July/August 1967 images.