Natural Acts: A Sidelong View of Science and Nature - David Quammen (1996)


Desert Sanitaire

THE ENGLISHMAN T. E. LAWRENCE, he of Arabian fame, was supposedly once asked why he so loved the desert. Skeptical historians have treated Lawrence far less kindly than Peter O’Toole and David Lean did, suggesting that far from being the reluctant demigod and charismatic catalyst of Arab revolt, as so appealingly pictured, he was more on the lines of a conniving, ambitious, and perpetually mendacious poseur. Also, unlike O’Toole, he stood only five foot three. To hear it from some of his biographers, the truth was not in Lawrence. He colluded with Lowell Thomas (in those days a young showman, more interested in dashing romance than journalistic fact) toward inventing and spreading the “Lawrence of Arabia” legend. He was a sadomasochistic neurotic whose entire life, say the critics, was “an enacted lie.” He liked costumes and he invented his own heroism.

This revisionist view, sound in principle, may in fact be a little too harsh. Lawrence certainly had something, and maybe that something was almost as valuable as the habit of veracity or full mental health. He had panache. He had high style. He had the gift for capturing, if not strict autobiographical truth, at least the human imagination. Why do you love the desert? they asked him later, when he was languishing through his self-imposed obscurity back in soggy, dreary England. Reportedly he said: “Because it’s clean.”

At least, I hope he did.

Of course, by a literal reading the notion is nonsense. Clean of what, dirt? Not if dust and perspiration and a week’s funky unwashed body grime can be counted. Clean of microbial infestation and many-legged vermin? Hardly. Perhaps clean of human infestation? That’s more plausible as a guess of what he meant, given the misanthropic side of his disposition. Anyhow, if you have ever spent time out there—not in Arabia, necessarily, but in the desert—down on the very ground, crunching off the miles with your boots, maybe you understand something of what poor troubled Lawrence was getting at.

It’s clean. It’s austere. It’s ascetic. Harshly infertile and fatally inhospitable. Solitary. Unconnected. It’s notable chiefly for what it lacks. America’s own preeminent desert anchorite seems to agree: Wherever his head and feet may go, says Ed Abbey, his heart and guts linger loyally “here on the clean, true, comfortable rock, under the black sun of God’s forsaken country.” It’s clean.

But what is it, this thing of such noteworthy cleanliness? “There is no single criterion,” according to the renowned desert botanist Forrest Shreve, “by which a desert may be recognized and defined.” Still, we have to start somewhere. And a desert is one of those entities, like virginity and sans serif typeface, of which the definition must begin with negatives.

In this case, lack of water. Not enough rain. Less than ten inches of precipitation through the average year. A desert is not, most essentially, a hot place or a sandy place or a place filled with reptiles and cacti and dark-skinned people wearing strange headgear. Fact number one is that it’s a dry place. Joseph Wood Krutch has written that “in desert country everything from the color of a mouse or the shape of a leaf up to the largest features of the mountains themselves is more likely than not to have the same explanation: dryness.” From such a simple starting point, things get more complicated immediately.

The matter of sheer dryness, for instance, is less crucial than the matter of aridity, which is a measure of how much or how little water remains available on a particular landscape surface for how long. Ten inches of rain distributed evenly throughout a lengthy cool season will support plants and animals in modest profusion; ten inches dumped from a great cloudburst on one summer afternoon, then not another drop for the rest of the year, will produce a few hours of wild flooding and leave behind a typical parched desert, with wide empty arroyos and a scattering of peculiarly specialized creatures. Whatever water there may be comes and goes quickly in a desert, erratically, never remaining available over time. It abides not. It pours off the slopes of treeless mountains. It gathers volume in drywashes and roars peremptorily away. It soaks down fast through the sandy soil and is gone. Most of all, it evaporates.

That’s the other prerequisite for any desert environment, lesser partner to dryness: evaporation, as wrought by heat and wind. A little rain falls occasionally, yes, but coming as it does in prodigal storms during the warmest months, burned off by direct sunshine and sucked away by the winds, the stuff disappears again almost at once. A system of land classification devised by Vladimir Köppen takes this into account, with a mathematical formula by which temperature and precipitation are together converted to an index of aridity. According to the Köppen method, any region where potential evaporation exceeds actual precipitation by a certain margin can be considered a desert. This rules out frigid locales with scant annual precipitation but plenty of permanent ice, such as Antarctica. Most of our own Southwest qualifies resoundingly.

But what, in the first place, makes a spot like Death Valley or Organ Pipe Monument so all-fired dry? Or a huge region like the Sahara? Or the Kalahari? Or the Taklimakan Desert of western China? Is it purely fortuitous that one geographical area—say, the Amazon basin—should receive buckets of moisture while another area not far away—the Atacama Desert in northern Chile—gets so little? The answer to that is no: not at all fortuitous. Three different geophysical factors combine, generally at least two in each case, to produce the world’s various zones of drastic and permanent drought: 1) high-pressure systems of air in the horse latitudes, 2) shadowing mountains, and 3) cool ocean currents. Together those three cast a tidy pattern, north and south, girdling our planet with deserts like a fat woman in a hot red bikini.

Don’t take my word for this: look at a globe. Spin it and follow the Tropic of Cancer with your finger as it passes through, or very near, every great desert of the northern hemisphere: the Sahara, the Arabian, the Turkestan, the Dasht-i-Lut of Iran, the Thar of India, the Taklimakan, the Gobi, and back around to the coast of Baja. Now spin again and trace the Tropic of Capricorn, circling down there below the equator: through the Namib and the Kalahari in southwestern Africa, straight across to the big desert that constitutes central Australia, on around again to the Atacama and the Monte-Patagonian of South America. This arrangement is no coincidence. It’s a result, first, of that high-pressure air in the horse latitudes.

The horse latitudes (traditionally so called for tenuous and uninteresting reasons) encircle Earth in a pair of wide bands, one north of the equator and one south, along those two lines, Cancer and Capricorn. The northern band spans roughly the area between latitudes 20° N and 35° N, and the counterpart covers a similar area of southern latitudes. Between the two bands is that zone loosely called “the tropics,” very hot and very wet, where most rainforest is located. This is also the zone of terrestrial surface that—because of its distance from the poles of rotation—is moving with greatest velocity as our planet spins through space. (The equator rolls around at better than 1,000 mph, while a point near the North Pole travels much slower.) For physical reasons only slightly less obscure than Thomistic metaphysics, the difference in surface velocity produces trade winds, variations in barometric pressure, and a consistent trend of rising air over the tropics. As the air rises, it grows cooler, therefore releasing its moisture (as cooling air always does) in generous deluge upon the tropical rainforests. Now those air systems are high and dry: far aloft in the atmosphere and emptied of their water. In that condition they slide out to the horse latitudes, north and south some hundreds of miles, and then again descend. Coming down, they get compacted into high pressure systems of surpassing dryness. And as the pressure of this falling air increases, so does its temperature. The consequence is extreme permanent aridity along the two latitudinal bands and a first cause for all the world’s major deserts.

The second cause is mountains—long ranges of mountains, sprawling out across the path of prevailing winds. These ranges block the movement of moist air, forcing it to ascend over them like a water-skier taking a jump. In the process, that air is cooled to the point where it releases its water. The mountains get deep snow on their peaks and the land to leeward gets what is left: almost nothing. Such a “rain shadow” of dryness may stretch for hundreds of miles downwind, depending on the height of the range. It’s no accident, then, that the Sahara is bordered along its northwestern rim by the Atlas Mountains, that the Taklimakan stares up at the Himalayas, that the Patagonian Desert is overshadowed by the Andes.

Ocean currents out of the polar regions work much the same way, sweeping along the windward coastlines of certain continents and putting a chill into the oncoming weather systems before those systems quite reach the land. Abruptly cooled, the air masses drop their water off the coast and arrive inland with little to offer. For instance, the Benguela Current, curling up from Antarctica to lap the southwestern edge of Africa, steals moisture that might otherwise reach the Namib. The Humboldt Current, running cold up the west coast of South America, keeps the Atacama similarly deprived. The California Current, flowing down from Alaska along the Pacific coast as far south as Baja, does its share to promote all-season baseball in Arizona.

Beyond all these causes of dryness, another important factor is wind, helping to shape desert not only through evaporation but also—and more drastically than in any other type of climate zone—by erosion. Powerful winds blow almost constantly into and across any desert, with heavier cold air charging forward to fill the vacuum as hot light air rises away off the desert floor. Desert mountains tend to increase this gustiness, and in some cases to focus winds through canyons and passes for still more extreme effect. In deserts of southwestern North America, they call the wind chubasco if it’s a fierce rotary hurricane of a thing, whirling up wet and mean out of the tropics and tearing into the hot southern drylands with velocities up to 100 mph, sometimes delivering more than a year’s average rainfall in just an afternoon. More innocent little whirlwinds, localized twisters and dust devils, are known as tornillos. The steadiest and driest wind out of northern Africa is known as sirocco, from an Italian word with an Arabic precursor; the sirocco is what gives southern Europe a sniff of Saharan desiccation. Besides raking away moisture and making life tough for plants and animals, winds work at dismantling mountains, grinding rock fragments into sand, piling the sand into dunes and moving them off like a herd of sheep. The writer and photographer Uwe George has called desert wind “the greatest sandblasting machine on earth,” and there is vivid evidence for that notion in any number of desert formations.

The winds and the flash floods are further abetted, in punishing the terrain, by huge fluctuations in surface temperature. A desert thermometer doesn’t just go up, way up; it goes wildly up and down, by day and by night, because the clear skies and the lack of vegetation allow so much of the day’s solar energy to radiate away after dark. Easy come, easy go, since there’s no insulation to slow the transfer of heat. The temperature of the land surface, furthermore, fluctuates even more radically than the air temperature; a dark stone heated to 175°F in the afternoon may cool to 50°F overnight. The result is a constant process of fragmentation—rocks splitting noisily, as though from sheer exasperation.

It is all so elaborately and neatly interconnected. The dryness of desert regions entails clear skies and a paucity of plants; which together entail fierce surface heat by day, bitter chill by night; which leads to rock fracture, crumbling mountains, and the eventual creation of sand. The thermal convection of air brings strong winds, which exacerbate in their turn the aridity and the erosion; the irregularity of rainfall, acting upon soil not anchored by a continuous carpet of plants, creates arroyos, canyons, badlands, rugged mountains; wind and sand collaborate on the dunes and the sculpted rocks. Add to this a team of small, thirst-proof animals like the kangaroo rat, hardy birds like the poorwill, ingeniously appointed reptiles like the sidewinder, arthropods of all menacing variety, and what you have is a desert—a land of hardship, of durable living creatures but not many, of severe beauty, and in some ineffable way, yes, of cleanliness.

In Seven Pillars of Wisdom, Lawrence wrote of the desert-dwelling sort of man who had “embraced with all his soul this nakedness too harsh for volunteers, for the reason, felt but inarticulate, that there he found himself indubitably free. He lost material ties, comforts, all superfluities and other complications to achieve a personal liberty which haunted starvation and death. He saw no virtue in poverty herself: he enjoyed the little vices and luxuries—coffee, fresh water, women—which he could still preserve. In his life he had air and winds, sun and light, open spaces and a great emptiness. There was no human effort, no fecundity in Nature: just the heaven above and the unspotted earth beneath. There unconsciously he came near God.”

Lawrence was talking about the Bedouin, but it might apply just as well to mad dogs and Englishmen, including himself. No cool distant tone of the anthropologist in those sentences, but an intimacy that sounds autobiographical (except for the sly comment about women, which didn’t suit his own taste in “little vices”) and more than a bit nostalgic. There unconsciously he came near God. Maybe that’s what Lawrence meant with his notion of cleanliness: For him, life in the desert had been next to godliness.