|Freshwater Resources in Arid Lands (UNU, 1997, 94 p.)|
|2: Negev: land, water, and civilization in a desert environment|
In antiquity the desert was regarded as a world unto itself, an extraterritorial realm separate from and additional to the other two known realms - the seas and the habitable rain-fed lands. The settled and "civilized" residents of the latter viewed the nomadic and "wild" people of the desert with fear and hostility, perceiving them to be a threat to civilization - as, indeed, they often were. The desert itself was held in awe as a place of terror, a largely useless and dangerous domain. One ventured into its mysterious vastness only at great risk. The desert's forbidding character has also been a challenge: a defiance of civilized mankind's self-proclaimed mastery of the earth; a barrier to human expansion, to progress, to economic development; a fortress holding out against colonization, against life itself.
But just what do we mean by the term desert? In what sense does it differ from what is commonly called an arid zone? Aridity in general is an imbalance between the demand for water and its supply, the supply being too scarce to meet the demand. Obviously, there can be different degrees of aridity. Such are the vagaries of climate that even so-called humid regions can experience occasional drought and even prolonged dry spells, though a humid region, by definition, is one in which annual precipitation is generally sufficient to sustain crop plants and, at times, may even be excessive. A semi-arid region is one in which precipitation is sufficient in most seasons but in which droughts (causing crop failure) occur frequently enough to make rain-fed farming a somewhat hazardous venture. An arid zone is one in which rain-fed farming is marginal successful in a few years but so frequently unsuccessful as to make the practice of rain-fed farming a highly insecure venture.
In arid regions, ironically, the crop plants' requirements for water are greatest just where the supplies by natural precipitation are the least. In such regions, therefore, the scales are weighted heavily against agriculture from the outset. The imbalance must be rectified by augmentation of water supply (i.e. irrigation), whenever possible, and by strict water conservation at all times. Despite the ever-present hazard of drought, farming populations can and do exist there, however precarious their economy. Extensive grazing - in addition to crop production and, occasionally, in preference to it - becomes a major form of land use in such areas.
The situation is fundamentally different in real desert areas, which are extremely arid. Here, even the precipitation in an average year - let alone in a drought - is definitely insufficient to sustain agricultural crops, so regular rain-fed farming is impossible. Hence, the biblical definition of the desert as "the land unsown." Even extensive grazing is marginal or submarginal. For humans to subsist in a desert without having to import most of their vital requirements, they must devise ingenious stratagems to obtain supplementary supplies of water, either by wresting the precious fluid from underground aquifers, if available, or by collecting it off the slopes of barren ground during brief episodes of rainfall, or by conveying it from another region. Only by such means can agriculture become possible, and then only on a fraction of the land area.
Though the word is derived from the Latin term for "deserted" or "abandoned," deserts are not totally useless wastelands. In fact, some deserts were settled by extraordinarily diligent and ingenious people, who proved that civilization can be established even in extremely difficult circumstances. Evidence of such civilizations can be found in the American South-West, in North Africa, in Arabia, in Jordan, and - notably - in the Negev Desert of southern Israel.
In the original Hebrew, the name Negev denotes dryness. As deserts go, it is rather small, constituting only a minuscule part of the great desert belt of North Africa and South-West Asia. Being on the fringe of this desert belt, much of the Negev is not an exceedingly dry desert. The mean annual rainfall varies from 200 mm in the north-west to about 25 mm in the far south, and is confined to the winter months, November to April. The distribution of rainfall within the rainy season is highly irregular, and the total seasonal amount fluctuates widely from year to year.
The Negev's historical importance derives from its geographical position as a narrow land bridge connecting Asia and Europe on the one hand, with Africa (Egypt) on the other. Hence, it has always served as a crossroads of trade and traffic between the continents. The advantages of controlling the region, however, were frequently offset by the disadvantages. The same routes that made trade possible and opened up cultivable areas to civilized settlement in times of peace were the ones followed by invading armies in times of war.
Moreover, neighbouring desert nomads were always ready to plunder the settled land and its inhabitants. Thus, to the difficulties posed by the paucity of water, the erodible soil, and the fragile vegetation, was added the requirement of constant vigilance against the danger of encroachment by hostile forces.
The long history of human habitation in the Negev began, evidently, during the Chalcolithic Age, and continued, intermittently, throughout the Bronze and Iron Ages. It includes the early Israelite period, as reflected in the biblical accounts of King Solomon and his Judaean successors - Asa, Jehoshaphat, and Uzziah. Some time after the destruction of the Kingdom of Judah by the Babylonians (in the sixth century before the Christian era [B.C.E.]), a new nation took possession of the Negev - the Nabateans. They built a magnificent civilization there, the achievements of which excite the imagination and admiration of visitors to the region to this day. Starting as nomadic traders, the Nabateans in time became superb architects and engineers, as well as expert hydrologists and diligent cultivators.
The Nabatean domain lay astride the important ancient trade routes between Arabia in the south and Syria in the north, and between the Orient, including India, and the Mediterranean world. These were the routes along which camel caravans transported spices and silks, ivory and incense, frankincense and myrrh, and medicinal herbs- commodities as prized in antiquity as are perfumes, cosmetics, and drugs today. Spices were more highly prized then than now, not so much because people in ancient times had preferred stronger tastes than we do, but because canning, refrigeration, and other means of food preservation that we take for granted were then unknown, and food could quickly become inedible without a heavy dosage of spice.
Caravans passing through the desert needed stopping places where they might rest and obtain water and provisions. To secure and supply their trade, the Nabateans therefore had to establish and maintain regularly spaced bases along their main routes, at important crossroads with secure sources of water. These bases gradually grew into permanent self-supporting villages and eventually into towns, and the Negev became more densely populated than ever before. Although the Nabateans' capital, the fabled red city of Petra, was built in the Edomean mountains (in what is today the Kingdom of Jordan), their population was centred in the Negev, where they built six major cities and numerous smaller villages. To maintain a population of many thousands, the Nabateans perforce had to develop agriculture in order to ensure a livelihood for their people. The same population continued even after the Romans annexed the region and made it a frontier province. And after the division of the Roman Empire and the establishment of Byzantium, the entire eastern realm of the empire enjoyed a period of stability. The Negev became still more densely populated, and the technical achievements of the era surpassed even those of the Nabateans when they were independent.
The eclipse of that civilization in the Negev came in the seventh century. Following the Moslem conquest in 636 C.E., the disruption of the old order and its links to the Mediterranean world caused the population to dwindle. Desert nomads took over and ushered in a long period of retrogression and poverty. Where thousands once prospered, a few hundred now eked out a bare subsistence. Magnificent monuments were prised apart, or crumbled gradually into haphazard heaps of stone. Great cisterns were choked by dust, and strongly built dykes were loosened by time and left unrepaired. Complete farm systems were left untended and allowed to disintegrate. Overgrazing the dry stream beds caused erosion, so that the formerly wide bottomlands irrigated by waterspreading methods became narrow, gouged-out gullies. Terraces once green with crops were left high and dry while torrential floods rushed uncontrolled through breached dykes and scoured the creeks. Thus, the best efforts and experience of generations of diligent people were wasted by neglect and abuse. The casual visitor to the Negev finds it difficult to understand how the ancients could have developed so grand a civilization in the midst of such barrenness. Only a careful study of their techniques can reveal the answer.
Permanent rivers are totally absent in the Negev, and even springs or proper locations for digging shallow wells are few and far between. Hence, the major source of water for humans and animals could only be the collection of surface run-off obtained from sloping ground during winter rains, a task that has been called "water harvesting." The ability to collect and store potable water from runoff was the first imperative of desert settlement. This was done by means of cisterns, which are artificially constructed reservoirs filled by directed surface flows during each infrequent rainstorm. Building efficient cisterns became possible after the advent of watertight plaster, the recognition of suitable rock formations, and the proper construction of channels to collect and divert overland flow.
Where cisterns could be located along the rim of a natural watercourse, they were filled by flash floods. However, most cisterns in the Negev were hewn into hillsides and depended on the direct collection of run-off. Many hundreds of such cisterns were built in the Negev, and they are clearly discernible landmarks even today. A typical hillside cistern resembles a giant necklace, with the glistening white pile of excavated rock seeming to hang as a pendant from the two collection channels that ring the hill and curve down its sides from opposite directions. To the thirsty ancient traveller, to whom these cisterns beckoned from afar, no sight could be more gladdening.
Run-off water was also used for irrigating crops. The run-off from winter rains falling on adjacent slopes was gathered and directed to bottomland fields for periodic soakings, to accumulate and store sufficient moisture in the soil to produce crops. Although the Negev's average winter rainfall is only about 100 mm, the run-off farmers were able to gather and concentrate sufficient run-off from the barren slopes to develop intensive agriculture in the depressions and bottomlands, which constituted only some 5 per cent of the total area in the northern Negev Highlands subregion.
This ingenious type of agriculture is called "run-off farming." Whereas farmers in more humid regions aim to have the soil absorb all the rain where it falls, thus preventing run-off, the desert farmers worked on the opposite principle: their aim was to prevent the rain from penetrating the soil on the slopes, so as to produce the maximum possible amount of run-off. They then collected this run-off from a large area of slopes and directed it to a relatively small cultivated area in the bottomlands.
The cultivated area was usually divided into small field plots, which were levelled and terraced to ensure the efficient spreading of water as well as the conservation of both water and soil. The oldest version of run-off farming probably consisted of terracing the small creek beds that collected the run-off naturally. Terracing transformed the entire length of each creek into a continuous stairway, with stairs perhaps 10-40 metres wide and 20-50 centimetres high. The terrace walls were designed to spread the flood and to prevent erosion. The slowed-down cascade from one terrace to the next could thus irrigate the field plots sufficiently for a crop to be grown. Distinct groups or series of terraced plots, having definable catchment areas and surrounded by stone walls, formed integral farming units of perhaps several hectares of cultivated land. The remains of hundreds of such farm units are spread throughout the Negev Highlands, most commonly around the principal ancient towns.
Detailed observation of ancient run-off farm units reveals that each unit was served by a particular well-delineated portion of the watershed. An elaborate system of conduits was constructed to collect run-off from specific sections of the adjacent slopes, not merely for each farm but, indeed, for each terraced field within the farm. The complete farm unit comprised both the slope catchment (the run-off-contributing area) and the bottomland fields (the run-off-receiving area). Fields could be made productive only if associated with a catchment from slopes, since the meagre rainfall alone was far from sufficient for any crop. The larger the catchment, the greater the water supply one could expect and the corresponding plot of land that could be irrigated. Clearly defined catchment areas, allocated to serve particular farm units, constituted "water rights," as specified in the ancient documents found in the region.
Typical farm units consisting of 0.5-5 hectares were associated with 10-150 hectares of sloping watershed. The ratio of run-off-contributing catchment to runoff-receiving crop land varied from 20:1 to 30:1. If each hectare of sloping land contributed only 10 per cent of its annual rainfall of 100 mm, then the receiving crop land would have gotten approximately 25 x 10 mm = 250 mm. Added to its own reception of the annual 100 mm of rainfall, the plot would thus have received a total of 35 mm, just enough to produce a crop. If, however, the run-off yield constituted 20 per cent of annual rainfall, the amount of water received by the field could equal 500 plus 100, for a total of 600 mm, an amount equivalent to the rainfall of the relatively humid habitats along the Mediterranean coast of Israel.
The fraction of rainfall yielded by any given watershed varied, of course, from rainstorm to rainstorm and hence from year to year. Gentle showers contributed practically no run-off, whereas intense squalls might yield 30 per cent or more of their rain. So, even with all the alertness, ingenuity, skill, and diligence they could muster, the run-off-farmers of the Negev operated a risky business and had to face new uncertainties each season. It is all the more remarkable, therefore, that they were able to cope with all the difficulties and to sustain a viable agricultural economy for so long on such a scale. That scale is worth emphasizing: during its period of maximal development in the Byzantine era, the system of run-off farming encompassed practically all of the usable land in the northern Negev Highlands.
The Negev run-off farmers apparently did more than merely gather natural runoff: we have clear evidence that they actually tried to induce more of it. The hillsides in the Negev, as in many other deserts, are naturally strewn with a pavement of stones and gravel, and this covering inhibits and detains the flow of run-off over the surface. The ancient Negevites deliberately cleared the stones off the slopes and thus smoothed the surface and exposed the finer soil, to facilitate the formation of a self-sealing crust. Consequently, we find countless heaps, mounds, and strips of gravel on many hillsides, particularly in the vicinity of the old towns of Shivta, Ovdat, and Nitzana. Our own field trials in that region have shown that the practice of removing the surface gravel can increase the run-off yield by 8-20 per cent.
The ancient Negev dwellers also carried out larger-scale works to divert flood water from regional streams onto adjacent flat lands. However, such works were inherently more difficult to construct and maintain. Moreover, because of the totally unpredictable and occasionally violent nature of the flash floods, the harnessing of such floods was fraught with much greater risk than the handling of small and controllable flows off hillsides.
The ancient desert civilization of the Negev, however remarkable, is not entirely unique. Other deserts in the Middle East and elsewhere witnessed similar (though not identical) developments. One example is that of the Anasazi (Pueblo) Indians of the American South-West. Though removed in space and time from the Nabateans, the Anasazi had to contend with similar environmental conditions. The Anasazi (meaning "Ancient Ones" in Navajo) developed from about 100 C.E. in the area where the boundaries of Arizona, New Mexico, Colorado, and Utah intersect. The early Anasazis supplemented hunting and wild-seed gathering with the cultivation of maize, pumpkins, and beans. Later, hunting and gathering were abandoned and agriculture became the major occupation, and this included the production of cotton. The Anasazi developed a system of run-off utilization that resembled that of the Negevites to a remarkable degree.
Notwithstanding its early success, the Anasazi civilization began to decline in the twelfth century. Not much later, these remarkable people abandoned their great cliff houses, storage pits, and ceremonial chambers, and no one to this day is quite sure why. The demise may have resulted from the incursion of nomadic tribes from the north. Another possibility is that denudation of the catchments may have led to depletion of game and to accelerated erosion, gullying, and subsequent lowering of the water-table, all of which might have reduced the productivity of the land. More plausibly, the Anasazi may have succumbed to the worst enemy of all people living in arid regions - a severe and prolonged drought. The Anasazi system of run-off farming and grain storage was capable of coping with short-term periods of dryness, but probably could not survive a decades-long span of water deficiency. Such a prolonged drought would have been especially debilitating if it were preceded by an extended period of abundance and prosperity, during which the population might have grown beyond the number that could be sustained indefinitely in such a basically arid region.
Whatever the circumstances attending the decline of the ancient civilizations of the desert, the basic principles of their pioneering methods of land and water husbandry may well be relevant today. In many of the desert fringelands around the world, where more people than ever are now struggling with the age-old problems of aridity, the old principles can be adapted and applied to great benefit. Much can be done to improve water harvesting and storage by means of modern technology. Power-driven earth-shaping machinery can be used to build parallel dykes across the slope, and to direct and spread overland flow. Moreover, stable chemical agents can be used to seal, waterproof, and stabilize run-off-yielding surfaces, as well as water reservoirs. Provision can be made for the eventuality of drought by storage of water and grain, by conservation and judicious tapping of underground water resources (aquifers) for supplementary irrigation, and by keeping range-land reserves.
We end with a word of caution. Modern means should be employed with great care, so that the localized utilization of land and water resources in restricted areas for the benefit of humans will not endanger the larger desert environment with its inherently fragile ecology and diverse biota. Humanity and nature can and must coexist, in the desert as elsewhere.
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