List of Projections:

not covered during lecture period:

17 - Motivation for construction of Aswan High Dam.
18 - Short term impacts of Aswan High Dam construction.
19 - Long term impacts of Aswan High Dam construction.
20 - Map of Lake Nasser.
21A - Zone of sediment deposition in Lake Nasser.
21B - Volume of water storage in Lake Nasser (1968-1990).
22 - Water demands per capita - I: drinking & domestic (NYC).
23 - Water demands per capita - II: irrigation (Egypt).
24 - Water demands per capita - III: summary of main use categories.
25 - Land area required for per capita food production (Egypt).
26 - Groundwaters in North Africa - fossil water from glacial period.
27 - Irrigation water demand (Egypt) per unit of land - duration of fossil groundwater resource if withdrawn for irrigation.

LARGE-SCALE METEOROLOGY RELEVANT TO THE NILE RIVER.

The upward movement of warm, moisture-laden (high water vapor content) air, and the subsequent cooling of the rising air parcels, leads to formation of large amounts of rain. As water vapor condenses to rain drops, the solar energy absorbed during evaporation of liquid water from the sea surface is released to the air (opposite to the "heat of vaporization"), adding additional heat to that already being delivered to the sub-tropical and equatorial zone by direct solar radiation. This additional source of energy input leads to even more heating of the air, and hence more upward movement (convection) of the air. This, in turn, causes further cooling of an air parcel as it ascends further in the atmosphere, and formation of additional precipitation. The interaction of natural atmospheric processes in the Inter Tropical Convergence Zone (ITCZ) is an example of a general type of phenomenon that is sometimes referred to as "positive feedback". Thus displacement of the moist equatorial air upward results in a series of processes that cause upward displacement to be enhanced. An opposite type of situation might be represented by a rubber band. When it is stretched to greater length from that to which it returns in the absence of extension, the force necessary to continue the stretching process is increased, leading quickly to either equilibrium between extension and contraction forces, or to rupture of the material if the extension force is too large. Such a situation can be considered as "negative feedback" (assuming no rupture of the rubber band). Here, each additional increment of stretching tends to make it more difficult for the next equivalent stretching amount to occur. The equatorial atmosphere dynamics could be considered as something like a "reverse" rubber band, where each bit of stretching made the next increment easier to occur.

For the Indian Monsoon, one critical element which leads to such a large perturbation of the atmosphere and formation of large amounts of rainfall includes the lack of symmetry of ocean and land across the equator in the longitudes that include central Asia and India. To the north of about 20°N there is only land, while south of this latitude, there is only ocean until the extreme southern latitudes of the Antarctic sea ice (60°S). During northern hemisphere summer, the interior land surface of Asia is very hot, causing rapidly rising dry air to form very low air pressure at the surface. This large area of low pressure, which might be considered as a partial vacuum, leads to strong flow of surface air from over the Indian Ocean towards the land, similar to the dynamics of the land-sea breeze phenomenon that is common on a much smaller scale in many coastal areas during summer months. The air over the Indian Ocean which moves northward contains very large amounts of water vapor, due to the warm ocean and warm air temperatures. As this moist air encounters the huge land barrier of the Himalaya Mountains, it must rise. As it rises, an air parcel cools, becomes supersaturated in water vapor, and heavy rainfall begins.

As in the ITCZ, positive feedback also occurs on the windward (south) side of the Himalaya, causing enhanced vertical motion of the air as each increment of water vapor is converted to liquid water, releasing more heat energy to the air as rain is formed. By the time the surface air has passed over the high mountains and Tibetan Plateau, and moved into the lower elevations of Central Asia, it has lost much of its moisture and warms as it descends, making it much more difficult for rain to form. The barrier of extremely high mountains north of India, Pakistan and Bangladesh and the existence of very large areas of land to the north and ocean to the south of these countries, leads to very rainy summer months and very dry winter months, or "monsoon" precipitation patterns. Although there are important monsoon precipitation dynamics elsewhere as well, this phenomenon is most intense and has the largest geographical expression on the Indian subcontinent of anywhere in the world.

Both of the above types of atmospheric processes are important in the Nile basin, with equatorial high rainfall band generating the surface runoff that leads to formation of the White Nile, with relatively constant discharge throughout the year. The high rainfall over the Ethiopian plateau during summer months is also due to a monsoon precipitation process driven by intense summer heating of the large arid land area of North Africa to form a huge low pressure center. Moist air from the ocean over both the equatorial Atlantic and the Indian Ocean then flow inland and encounter topographic barriers, although much smaller than the Himalaya, that lead to intense precipitation that is responsible for the strongly seasonal discharge pattern of the Blue Nile .

GENERAL CHARACTERISTICS OF THE NILE RIVER DRAINAGE BASIN.

Key Concepts (Projection #2):

Nile River discharge in Egypt, the only major source of surface water in that country, is derived from rain in tropical latitudes influenced by the ITCZ (White Nile) and monsoon rain in Ethiopia (Blue Nile).

All Nile discharge is now controlled by storage behind dams (Egypt & Sudan) and used primarily for irrigation.

Food production in Egypt is not sufficient to meet domestic demand, even with total control of the Nile .

NILE RIVER HYDROLOGY AND IRRIGATION DIVERSIONS.

IRRIGATION DIVERSIONS FROM THE NILE RIVER IN EGYPT.

Some general characteristics of the irrigation water delivery process can be summarized in a block diagram indicating major functional steps (Projection #5). From one of the two branches of the Nile River in the Delta, water is directed through a series of irrigation canals of decreasing size, with flow driven by gravity until the immediate vicinity of the agricultural fields. At this point, the water is approximately 1.5 meters below the level of the soil surface, requiring each farmer to expend great effort (i.e. energy) to raise the water up nearly 2 meters to permit flow over individual fields. Until very recently, the dominant mode of raising the water was via animal power, but diesel pumps now provide an increasing proportion of the energy source for this activity. Clearly one of the major incentives for efficient use of irrigation water in the Nile Delta has been the large expenditure of energy, either in animal power or diesel fuel, required to deliver water in the final transfer step to the fields, since little of the cost for irrigation water has historically been assessed directly to individual farmers. Thus the physical design of the irrigation water delivery network has served to reduce withdrawals of excess water because of the very high cost in effort by individual farmers to lift water on the fields for irrigation.

A similar block diagram for the drainage network can also be sketched (Projection #6). Again, nearly all of the transfer through the system is by gravity, except for the final stage of lifting by electrical pumps back above sea level for flow into the Mediterranean Sea. Here, the central government is responsible for the costs and operation of drainage water removal, as also was true for storage of water behind the High Dam at Aswan and for the delivery of irrigation water to the immediate vicinity of the agricultural fields.

CHANGES IN NILE RIVER WATER BUDGETS DUE TO IRRIGATION DIVERSIONS.

The most dramatic event in the history of irrigation in Egypt occurred in the mid 1960's, when the High Dam at Aswan was completed, permitting continuous cropping throughout the Nile Delta (Projection #7). The reservoir behind the High Dam (Lake Nasser) is so huge that it permits storage of several years of average flow of the Nile River, completely eliminating the natural annual cycle of flooding in Egypt. Some idea of the year to year variations of Nile River discharge at Aswan can be gained by examining the record for the years 1912-1973 (Projection #8). The change in annual Q initiated by construction of the High Dam in the mid 1960's is readily apparent in a substantial drop in mean flow, due to evaporation losses in Lake Nasser and initial water storage behind the High Dam at Aswan. Secondly, the large year to year variations have been completely eliminated. Even more dramatic is the change in the natural cycle of river discharge within a year (Projection #9A) for the period prior to construction of the High Dam (1912-1964) to that after discharge regulation was completed (Projection #9B). Note that the total amount of Nile water passing into the populated area of Egypt immediately after completion of the High Dam was considerably less than prior to construction of the High Dam, as the result of large evaporation losses from Lake Nasser, as well as accumulation of storage water in Lake Nasser.

At present, the most important new irrigation initiative in Egypt involves collection of irrigation drainage waters from the Delta for eventual transfer to new agricultural areas in the northern Sinai, often referred to as "reuse" of drainage waters. The salinities of some of these drainage waters are low enough (TDS = 700 to 1000 ppm) to permit another cycle of use in irrigation agriculture before discharge to the Mediterranean Sea.

The only future project for additional control of Nile waters which is frequently discussed is construction of a bypass canal in southern Sudan (Jonglei Canal). This would allow a much greater fraction of White Nile water to pass through the region of the Sudd, where it is lost by evaporation and transpiration, eventually reaching large irrigation districts in northern Sudan near the junction of the White and Blue Nile and further downstream in Egypt. However, if such a diversion were to occur, it would result in drainage of the vast swamp covering the Sudd and greatly impact the natural vegetation, animal life, and human life of that region. The inhabitants of the Sudd are almost universally opposed to this project, and the resulting conflict over water resources is at the heart of an ongoing civil war in southern Sudan. Alteration of surface water allocations are literally matters of life and death in this part of the Nile basin, as they often are in other arid regions. Here is one of the most dramatic types of environmental policy decisions affecting river water allocation. In order to provide more irrigation water for Egypt and northern Sudan, it would be necessary to completely alter the ecology, both human and nonhuman, of the southern Sudan, by largely eliminating the most extensive freshwater swamp on the planet.

The evolution of control of Nile water for irrigation in Egypt during the 20th century can be examined by considering annual increments of water flux for various uses prior to and after construction of the High Dam at Aswan (Projection #10). Up until the early 1960's, the average annual amount of water reaching Egypt was about 65 km³, appreciably less than natural discharge of about 80 km³ due to upstream irrigation diversions in the Sudan. About one third of this volume was returned to the atmosphere by ET and about half discharged to the Mediterranean Sea through the two branches of the river in the Nile Delta (Rosetta and Damietta), mostly during the few months of annual flooding. After construction of the High Dam, average outflow through the river mouths declined to only about 6% of natural Q, while irrigation drainage discharge to the Mediterranean Sea became a factor of three greater than Nile outflow through the Rosetta branch near Alexandria. In addition to elimination of the annual flood, the huge addition in water storage capacity resulted in evaporation plus seepage losses in Lake Nasser of about 12 km³ per year.

The most extreme estimates of additional available irrigation water from the Nile to Egypt during the next century assume eventual construction of the bypass canal in southern Sudan and reuse of all of the lower salinity drainage water from the Delta in the northern Sinai. Such a scenario could conceivably expand irrigation water for Egypt by another 35 to 40% above current supplies available since completion of the High Dam in the mid 1960s. This appears to be the extreme upper limit to surface water supplies that might be developed for Egypt in the future, but would require taking away nearly all the water currently available to inhabitants of the Sudd. Thus to the first approximation, the entire discharge of the Nile River will have been diverted for human uses, primarily irrigation in Sudan and Egypt.

AGRICULTURAL CROP PRODUCTION IN EGYPT.

The largest area of crops annually planted in Egypt (about 12% of total crop area) is a clover (Projection #11), often called "berseem", that provides feed for animals used for lifting of irrigation water from canals up to the level of the fields and other cultivation activities and also for those animals raised for meat. This clover crop is grown in winter months, and preserved by drying in the sun for use throughout the year. As a plant that has nitrogen-fixing bacteria associated with its roots, berseem also adds nitrogen to the soil, raising fertility for subsequent crops. Grain crops account for the largest proportion of total crop area in Egypt, as they do throughout the world: maize (corn), wheat, rice, millet and barley. Cotton still remains the largest agricultural export of Egypt, as it has for much of the past two centuries. These crop data are presented in terms of annual crop areas planted, rather than in terms of annual production in tons, because animal fodder crops such as berseem (very high weight per unit of land since all of the plant biomass is included) are considered with human food crops such as wheat, where only the weight of the seeds actually consumed by people are usually reported.

The range of agricultural crops in Egypt is quite similar to that for the world as a whole. The most important sources of human food are a small number of grain and tuber (root) crops: wheat, rice, maize, potato, barley, sweet potato and cassava, accounting for more than three quarters of world crop production.

CROP YIELDS PER UNIT AREA IN EGYPT.

Wheat production per unit area in Egypt is also quite high (Projection #12), but the country is currently able to grow less than one quarter of the amount consumed by the population. Data for wheat production were included for a total of 53 countries, with the numbers in the lower, middle and upper income groups of countries being 18, 17 and 18, respectively. Egypt had the highest yield of wheat during the early 1980s for any other large population country (> 10 million in 1982) in its same economic category. The lack of ability of Egypt to produce sufficient wheat for domestic consumption of the crop that accounts for the largest single component of diet in the country is a clear indicator of the current very high demand for food by the large and growing population of Egypt. The country has not been able to produce sufficient wheat for domestic consumption for much of the second half of this century, but was able to acquire enough foreign exchange currency from international sales of cotton to purchase imported grain to balance the shortfall through about the end of the 1960's. By the early 1980's, Egypt had one of the highest rates of import of wheat per capita of any country in the world (Projection #13). Data for wheat imports were included for a total of 49 countries, with the numbers of countries in the lower, middle and upper income groups being 21, 16 and 12, respectively.

As the population of Egypt has continued to grow, the demand for food imports has far exceeded the ability to purchase grains from export sales of cotton. The primary source of foreign currency for grain imports now is derived from sale of petroleum, a commodity that Egypt cannot export in significant quantities for much longer due to rising domestic demand and depleted resources. Unlike a number of other Arab states near the Persian Gulf, Egypt has only limited resources of petroleum. There is no obvious source of foreign currency to replace petroleum sales for purchase of grain imports in the near future. Thus the supply and demand situation for the most basic of foods (grains) in Egypt is very uncertain only a decade or so in the future.

POPULATION TRENDS IN EGYPT AS A FUNCTION OF TIME.

If we consider the history of population in Egypt over longer time scales, the trends over the past two centuries are even more dramatic (Projection #15). Some scholars have estimated that Egypt had approximately 4 to 5 million people living along the Nile by about 2000 BC. There was slow net population growth throughout the classical era of Egypt civilization when the great monuments were constructed and many of the major cultural advances in early human history occurred in the Nile Valley. During the period of greatest expansion of the Roman Empire, Egypt was the primary food source derived from trade for much of the region. Thus for thousands of years, Egypt was able to produce sufficient food for its own population as well as derive income from export commerce involving agricultural production. The population of Egypt is thought to have grown to about 8 to 10 million around 1000 AD, and then began a major decline to the 3 million present at the beginning of the 19^th century. Causes of this decline in population are obscure, but plausible elements include extensive deaths by diseases such as bubonic plague that ravaged much of the densely settled world during the Middle Ages. Others have suggested that there was extensive deprivation of basic materials such as food to the native population of Egypt by occupying peoples of the Ottoman Empire. Whatever the causes, they were of sufficient magnitude to decimate the population to only about one-third of the maximum that existing during the first several hundred years of the Arab civilization of Egypt. Clearly populations of major countries do not always rise! When conditions are sufficiently bad, through some combination of disease and food deprivation, population can decline appreciably. It should be noted that estimates of population in Egypt prior to about 1800 AD are quite controversial. Some estimates suggest that the population around 2000 BC was only about 2 million, about half of that indicated here, and that the onset of decline was much earlier, beginning near the end of the Pharonic period. It is clear, however, that the late 20th century population of Egypt has approached values that are about an order of magnitude greater than the highest values achieved in the many thousands of years of earlier human history of the Nile Valley.

CURRENT POPULATION DENSITY IN EGYPT COMPARED TO OTHER COUNTRIES.

Some indication of the seriousness of food production problems facing Egypt can be derived from comparison of population to crop land area for a number of countries (Projection #16). The world average in the early 1980's was about 300 people per square kilometer of crop land, with both the USSR and the USA having population "densities" of only about 150 in the same units. At the opposite extreme were Japan (2400), Taiwan (2000), South Korea (1800), The Netherlands (1600) and Egypt (1600). Bangladesh (1000), China (1000) and India (400) all have appreciable more crop land per capita than Egypt. None of the other countries in the group with Egypt having very high ratios of population to crop land area can be considered as having agricultural economies today. They are all highly industrialized, have exports of technologically advanced goods as a dominant component of their economies, and thus have sufficient currency resources to purchase grains and other foods on the international market to meet domestic demand in excess of production. By this crude index of recent population relative to total crop land under production, Egypt appears to have one of the most difficult tasks of any country in the world in providing sufficient food from domestic production.

Some estimation of the lack of balance between capacity for food production and demand within Egypt can be gained from considering wheat production and consumption. Currently, more than three quarters of demand is supplied by imports. If exports such as cotton are considered, plus domestic production of other grains such as rice and maize, Egypt appears to be able to produce enough food or purchase from sale of exported agricultural goods enough food imports to supply a population of approximately 25 to 30 million, less than one half of the current population. Most projections of population for Egypt near the end of the 21^st century suggest likely numbers at least double current population, assuming rapid declines in birth rates comparable in rate of decrease to those which occurred in China and a few other countries over the past four decades. A recent World Bank projection of a hypothetical likely "stable" population in Egypt was 120 million, based entirely on demographic data. This latter estimate includes no consideration of the resource base need to provide food for that population. With all currently available water already diverted from the Nile for irrigation, nearly all potential crop land in the country intensively cultivated (there is no appreciable area dedicated primarily to animal grazing in Egypt), and food production rates per unit of crop land already among the highest of any country in the world, it is very difficult to be see how the the population of the country can be fed from domestic food production in the next century. This situation underlies all environmental issues of consequence in Egypt today and into the foreseeable future.

Key Concepts:

1. Long-term problems resulting from current surface water management practices, such as reservoir siltation, present major difficulties for future generations, but are generally ignored.
2. Irrigation demand for water is more than an order of magnitude greater than domestic use demand in arid climates.
3. Fossil groundwaters in N Africa and elsewhere are being withdrawn to supply irrigation demands in amounts far in excess of recharge rates.

OUTLINE OF SOME IMPACTS OF CONTROLS OF NILE RIVER DISCHARGE.

The most central argument for building a large reservoir on the Nile was to permit more intensive irrigation in the Nile Delta and upstream along the main stem of the river in Egypt. Storage of a total volume equivalent to two or three years of average discharge eliminated the "loss" of fresh water to the Mediterranean Sea during annual flooding, permitting all to be used for irrigation (except for evaporation losses from Lake Nasser). Secondly, in drought years of low Nile discharge to Egypt stored irrigation water could be used to sustain food production, assuming a limited number of low Q years. During the major drought in Africa of the mid to late '80s, many countries in the Nile River basin, including Ethiopia and Sudan, experienced major famine while Egypt did not, at least in part because of its ability to draw on irrigation water stored in Lake Nasser.

Another argument for construction of the High Dam was for generation of electricity. In the first decade after construction, there was sufficient supply of electricity to meet demands of urban citizens in Cairo and also some rural populations, with a surplus for smelting of aluminum ore. By the early 1980's, the demand for electricity had overtaken available supply, which was dominated by High Dam hydroelectricity, and construction of new fossil fuel burning generating stations began. Operation of these new generating stations will significantly shorten the lifetime of petroleum resources in Egypt, the sale of which currently provides a major component of the foreign currency for purchase of food imports.

Construction of the High Dam provided more options for location of homes and other buildings, as well as other infrastructure that would not have been feasible due to the elimination of the annual flooding cycle throughout the country. Thus it permitted many of the kinds of investments that are assumed to be necessary in our modern world.

Some immediate negative impacts of the High Dam construction included (Projection #18): loss of the coastal fishery for sardines and anchovies that were important food sources caught near the mouths of the two branches of the Nile. The Mediterranean Sea can be generally considered as a "desert" in terms of fish production, due to its very low supply of nutrients such as phosphorus and nitrogen that are required for the microscopic marine green plants to accomplish photosynthesis. As a result, marine fishing in Egypt had been important only in the immediate vicinity of the Nile outflow, especially in the months following annual flooding. Immediately after the High Dam was completed and the last Nile flood had occurred, the fishery of coastal Egypt collapsed, and has never recovered.

The most important building material in rural Egypt has always been bricks made from Nile River sediments, mostly obtained by dredging of the canal network following annual floods. After the floods ceased in the mid 1960's, there was no new supply of sediments to be cleared from the canals, and some farmers began to sell their top soil to small-scale brick manufacturing plants. Although this gave an immediate return of cash to the farmer who mined his fields for soil, it then took the land involved out of agricultural production, or made it much more difficult to use because of the need for very careful land-level controls for flood irrigation practices. This loss of land has been mostly arrested in the last two decades by mining clay deposits from surrounding desert lands that are not feasible to use for agriculture and building much larger brick factories that do not use Nile Delta soils as a raw material. However, this latter development had the negative consequence of eliminating a major source of income to the small-scale brick manufacturers, and transferring the income to large central government enterprises.

Much of the fertility of the agricultural soil in Egypt resulted from the continuous resupply of rich volcanic sediments from the Ethiopian highlands during annual flooding. Since this no longer occurs, it has become necessary to use much greater amounts of commercial fertilizers, such as mineral phosphates and fixed nitrogen. The latter of these nutrient sources is very energy intensive in terms of production so it represents another drain on Egypt's limited fossil fuel reserves and on foreign currency sources. Total annual commercial fertilizer use per hectare of agricultural land in Egypt during the early 1990's was about 340 kg, one of the highest in the world for any country of appreciable population. The comparable values during the same years for the USA and Japan were 100 kg and 390 kg, respectively. It appears unlikely that higher application rates of commercial fertilizer would significantly improve crop yields in Egypt.

LONG-TERM IMPACTS OF CONTROLS OF NILE RIVER DISCHARGE.

Lake Nasser is now steadily filling with sediments (Projection #20) that formerly reached the Delta and the coastal Mediterranean The current locus of deposition is far upstream of the High Dam and does not immediately threaten operation of the power station (Projection #21A). However, the reservoir will be sufficiently filled within less than a millennium to no longer be useful for storage of irrigation water. Order of magnitude estimates suggest that within about 600 years, about half of the current irrigation water storage value of Lake Nasser will have been lost. In terms of the history of civilization in the Nile Valley, this is not very long. The quantities of sediment filling up Lake Nasser are so huge (about 100 million tons per year) as to defy currently feasible attempts at removal. No one currently has a plausible solution to this problem, which has effectively been postponed for later generations to confront, as is true for many major environmental issues in other countries. The largest sediment dredging operations in the world to maintain some of the most valuable harbors, such as that for New York City, are one-two orders of magnitude smaller than would be required to remove the annual influx of sediment to Lake Nasser.

The record of monthly water volumes in Lake Nasser between 1968 and 1990 illustrate quite dramatically the years of rapid filling which occurred during the 1970's, followed by the major decline in storage volume associated with the drought of the 1980's (Projection #21B). By the time of the large flood runoff from Ethiopia in the summer of 1988, the active storage volume in Lake Nasser had decreased to less than 20 km3, only about 20% of the active volume available during the late 1970's. If the drought had continued another year, there would have been major shortfalls of water deliveries for irrigation agriculture in Egypt.

WATER DEMAND FOR DRINKING WATER: MINIMUM REQUIREMENTS.

Amounts of drinking water needed by an individual depend upon age, weight, level of physical activity, air temperature, humidity, elevation and many other factors. However, as an approximation, about 4 liters of fluids per day is required for an adult living in a temperate climate. This fresh (i.e. low dissolved salt content) water should be free of any disease-causing bacteria or other pathogens, as well as chemical contamination. A small additional amount of high-purity water is needed for cooking and other personal uses that could lead to disease if contaminated supplies were used. Summing these high-purity water demands, the minimum for each person can be approximated as about 10 liters per day (Projection #22). In situations of extreme water shortage, such as those typical of droughts in North Africa where rural populations must collect and transport all of their water over long distances, this quantity is about the minimum that can sustain human life for an extended period. Converting units of volume and time, 10 liters of water per day translates to about 4 cubic meters per year.

DOMESTIC WATER CONSUMPTION IN NEW YORK CITY.

Domestic water demands in Egypt are appreciably less than for NYC and other large cities in the USA, but the differences are less than might be expected. Estimates of total domestic water use in Egypt during 1976 were about 115 liters per capita per day. By 1982, per capita daily use had grown to about 180 liters for the country, but the equivalent use amount for Cairo was about 320 liters, slightly more than typical for European cities (300 liters per day per capita). Thus urban domestic water use does not vary as much as might be expected for large differences in economic circumstances.

IRRIGATION DEMAND FOR WATER IN EGYPT.

Egypt is currently able to produce food crops plus export crops such as cotton that are equivalent to only about half of food demand from the resident population. Thus, to obtain a value of irrigation water equivalent to total per capita food demand, the number derived above can be multiplied by two, suggesting that a more appropriate per capita irrigation water requirement is about 2000 cubic meters per year, assuming all food production occurs from irrigated crops.

SUMMARY OF WATER DEMAND (PER CAPITA) BY CATEGORY OF USE.

The high ratio of per capita irrigation use to that for minimum drinking plus cooking water (about 500 to 1) is indicative of the large amounts of water required for transpiration fluxes of crop plants, compared to those needed for direct consumption of humans. For Egypt, with the only significant source of renewable water supply being the Nile River, the largest quantities of water demand are always likely to remain in the category of irrigation. On the other hand, with diseases transmitted by contaminated water as a major health issue in the country, the quantities of clean water required to improve conditions of the population are much less than the total water demand for irrigation.

LAND AREA REQUIRED FOR FOOD PRODUCTION (PER CAPITA).

GROUNDWATER RESOURCES IN NORTH AFRICA.

Some of the evidence that establishes the likely periods of groundwater recharge involve measurements of the isotopic composition of the water molecules themselves. There are several stable isotopes of both hydrogen and oxygen in the natural environment, including deuterium (hydrogen with 1 neutron and 1 proton in the nucleus, as opposed to the most abundant hydrogen atom which has 1 proton and 0 neutrons in the nucleus) and oxygen-18 (oxygen with 10 neutrons and 8 protons as opposed to the most common form of oxygen which has 8 neutrons and 8 protons). The proportion of "heavy" isotopes (those with "extra" neutrons) in natural waters varies significantly from one area to another, due primarily to atmospheric processes involving evaporation and condensation. However, once water passes below the surface, away from influence of the atmosphere and into groundwaters, its stable isotopic composition no longer changes and it can retain the same relative proportion of "heavy" isotopes for millions of years. In contrast, the chemical composition of groundwaters can be modified substantially in the subsurface by dissolution of aquifer minerals or chemical precipitation of new mineral from solution. Thus much about the atmospheric transport history of water which recharged a particular aquifer is preserved indefinitely in the stable isotope composition of the water molecules and can serve as a "fingerprint" of that particular water resource. The stable isotope compositions of deep groundwaters beneath the Sahara are completely different from those of the modern Nile River, and are relics of a past climate that differed dramatically from that of the present.

A second line of evidence about the time of recharge of deep North African groundwaters involves the amount of carbon-14 (radioactive carbon with a half-life of 5600 years) remaining in the dissolved bicarbonate ion of these waters. The carbon-14 "age" of these water range from about 5000 to 25,000 years, based on the very low amounts of this radioactive isotope remaining dissolved in the water. Thus a consistent picture exists of the time of recharge of these waters that excludes the possibility of their being related to the "modern" hydrologic cycle of the region. They should be considered as being "fossil" waters that receive no significant recharge today.

The total amounts of water present in these deep groundwaters beneath the Sahara are large compared to the volume of water flowing in the Nile River each year, but actually represent a very limited resource when considered for potential use over an extended period since they are not being renewed in today's climate. With this knowledge in mind, some potential uses of this resource can be considered: irrigation, drinking water, other?

POSSIBLE USES OF FOSSIL GROUNDWATERS IN NORTH AFRICA.

Although this simple calculation suggests that extensive pumping of fossil groundwaters for irrigation supplies probably should be considered as the least economically valuable potential use of the resource, this policy has been exactly that planned in Libya. The same type of deep groundwater resource that lies under Egypt is also found beneath large areas of Libya and definite construction proposals have been made to pump that water out and into a large pipeline for irrigation of crops near the Mediterranean Sea in northeastern Libya. The wisdom of such a choice appears to be no less shortsighted for that country than it would be for Egypt, yet it remains as a major development goal for Libya. During the 1980s Saudi Arabia initiated large irrigation projects for grain production based on pumping of old groundwaters from beneath the deserts of that country. Thus despite the lack of a sustainable supply of irrigation water, large investments have been or are planned in the Middle East based on "mining" of fossil groundwaters.

Such shortsighted practices are not confined to oil-rich states with arid climates. Much of the irrigation expansion which occurred in the mid continent of the USA during the 20^th century in the states of North Dakota, South Dakota, Nebraska, Kansas, Colorado, Oklahoma, Texas and New Mexico is based on withdrawals from the largest continuous groundwater resource in North America, the Ogallala Aquifer. Although this groundwater resource currently does receive some limited recharge, the rate for most of the aquifer is less than half of current irrigation pumping. As the resource becomes depleted, beginning first with the states towards the southern end of the region, large investments in irrigation infrastructure will be abandoned and economic returns from farming in the region will contract dramatically. The process of rapid groundwater resource depletion has already reached the point that large areas producing high economic value crops based on "temporary" irrigation in the central USA have already been lost.

Without going into details, some other potential uses of fossil groundwaters in Egypt are worth exploring. One would be to use this water resource as a temporary source of high quality drinking water for populations that currently receive only untreated contaminated surface waters (about half of those living in the country). At present, USAID is heavily involved in delivering small-scale treatment plants for villages of 2000 to 3000 people that are based on filtration and chlorination of contaminated surface waters. These treatment facilities cost more than $50 thousand to install for each village unit, appreciable ongoing costs to operate and the necessity of expensive supplies such as chlorine to be purchased. Because of many difficulties of maintaining such equipment and obtaining chemical supplies, many of these small-scale domestic water treatment facilities were not operating as designed within a few years of construction, or are likely to go out of service completely. In contrast, if the same capital investments were made in providing groundwaters as a source of drinking water, a factor to ten greater population could be served with a supply that would not need to be treated at all to eliminate bacterial contamination because this water is already completely free of such organisms. If these high-purity "fossil" resources were used exclusively for drinking and cooking, the resource lifetime would be about a factor of 500 longer than for irrigation. By not having sufficient understanding of the natural environment to permit taking advantage of favorable circumstances for development, agencies that are intended to improve the lives of low-income populations in countries such as Egypt often use their limited economic resources very inefficiently. This is definitely the situation for rural water supplies in Egypt.

Considering some options for long-term sustainable energy resources for the world, another possible use of the fossil groundwaters in Egypt and other countries in North Africa could be considered. The Sahara Desert is the largest continuous area of intense solar radiation to the surface on the planet. Essentially cloudless for most of the year and having high influx of energy from the sun, this huge area would be ideal for construction of solar-electricity facilities. One proposal for storage of energy from solar-generated electricity is to split water molecules into hydrogen and oxygen by electrolysis. The hydrogen gas then becomes a valuable fuel that could be transported by pipelines or other means to sites of energy consumption, similar to current practice for natural gas. If such a possibility were to be pursued for the Sahara, the presence of high quality groundwater would probably make it more economically favorable. The total economic value of these groundwater resources might be many orders of magnitude greater as part of a large solar electric generation network for production of hydrogen as a portable fuel than for any of the currently proposed uses for irrigation.

OTHER DEVELOPMENT ISSUES RELATED TO RESOURCES IN EGYPT.

Egypt has a very limited supply of domestic petroleum resources, the sale of which on the international market is the greatest single source of foreign currency to the government of Egypt. Revenues from these sales of petroleum are used in large part for purchase of wheat and other basic foods. Completion of new oil-fired power stations will shorten the number of years until this source of purchasing power is eliminated and there will no longer be sufficient money to buy food that cannot be produced domestically. Here is a situation where the net effect of providing loans from international sources may make it more difficult for Egypt to adapt to the severe limits of its natural resources by shortening the period over which changes must be accomplished.