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Nile River control; food production & population in Egypt
List of Figures:
- Map of Nile River drainage basin.
- Key concepts: Nile Q sources, control & Egypt food production.
- World rivers: Q vs basin area, Nile River natural and modified.
- Nile Delta drainage network.
- Nile Delta irrigation flow schematic.
- Nile Delta drainage flow schematic.
- Outline of irrigation practices in Egypt.
- Annual variations of Q: 1912-1973.
- Mean monthly Q of Nile at Aswan 1912-1964.
- Mean monthly Q of Nile at Aswan 1968-1973.
- Annual water budgets in Egypt (table).
- Areas of crop production in Egypt (histogram).
- Wheat production per hectare by country.
- Wheat imports per capita by country.
- Population trends in Egypt: 1800 to 2000 AD.
- Population trends in Egypt: 2000 BC to 1985 AD.
- Ratio pop per unit area cropland, by country pop >10 million.
LARGE-SCALE METEOROLOGY RELEVANT TO THE NILE RIVER.
In previous lectures, some atmospheric processes involved in causing high rainfall rates in latitude bands near the equator (ITCZ) and on the Indian subcontinent (Indian Monsoon) were outlined. Both of these aspects of the global rainfall and river runoff pattern are important in the basin of the Nile River, so their dynamics will be reviewed briefly. On the scale of the entire planet, the largest annual amounts of rainfall per unit of surface area occur near the equator. This is a consequence of the flow of warm air at the surface towards the equator from both hemispheres at all latitudes between about 30˚ N and 30˚ S. The narrow band of convergence of these equatorward flows must, by necessity, also be a zone of rising air, since the influx of large masses of air near the ground surface must go somewhere. Since air cools as it rises, due to decreasing atmospheric pressures at higher elevation, each rising parcel of air can hold less water vapor than when it was at lower elevation. Remember that air can hold much more water vapor at higher temperatures, and thus surface air in the tropics flowing over the ocean towards the equator is able to accumulate large amounts of water vapor as strong evaporation occurs in zones of intense solar energy input.
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 that 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 that 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 than anywhere else in the world.
NILE RIVER HYDROLOGY AND IRRIGATION DIVERSIONS.
The Nile River, flowing through one of the most arid regions on the planet in the final third of its progress to the sea, has a natural discharge per unit area of drainage basin that is extremely low compared to other large rivers (Figure #3). The comparison of river discharge rates vs drainage basin areas, on a log-log plot, provides an indication of the departures of individual river systems from the general trend of the entire data set. Many of the large tropical and South Asia rivers, such as the Amazon, Orinoco, Brahmaputra, and Magdalena Rivers fall well above the general trend, indicating higher than average runoff per unit of basin area. In contrast, the Mississippi, Niger and Nile fall below the average yield of water per unit area of drainage basin. Amplifying the very low natural runoff from the Nile basin is the large intervention by human activities, primarily irrigation. The amount of water reaching the Mediterranean from the Nile is now less than 5% of its natural discharge. Thus, to the first approximation, the entire flow of this river is currently harnessed for human uses, as has also occurred for the Colorado River in the USA.
IRRIGATION DIVERSIONS FROM THE NILE RIVER IN EGYPT.
The irrigation system of the Nile Delta, which is responsible for about two thirds of total surface water diversion in Egypt, includes a very large distribution network, and also an extensive grid of drainage canals (Figure #4), analogous to the arteries (irrigation) and veins (drainage) in the human blood circulation system. The drainage canals provide the network which removes "waste products" from the farmer's fields, including soluble salts, to prevent buildup of salinity in the soils. The irrigation delivery of Nile water to the Delta is now so large per unit area of land that the groundwaters would reach almost to the soil surface if the drainage network were not in place, leading to water logging of the plant roots and collapse of crop productivity. The drains operate by gravity until the northernmost fringe of the Delta, where the downstream base of most of the canal systems are up to 3 meters below sea level. These drainage waters are then pumped up to sea level and discharged into the Mediterranean Sea using huge pumps that rival the size of small hydroelectric generating stations. Together they require for their operation between 5% and 10% of the electricity generated at the Aswan High Dam hydroelectric generating station in an average year. Total installed electricity generation capacity of the High Dam is about 2500 megawatts, about one quarter of that at the Itaipu site on the Parana River between Brazil and Paraguay.
Some general characteristics of the irrigation water delivery process can be summarized in a block diagram indicating major functional steps (Figure #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 (Figure #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 practice of irrigated agricultural has existed in Egypt for more than 6000 years. For most of that time water was delivered to individual fields by annual floods resulting from the summer monsoon rains in Ethiopia, when each farming family in the Nile Valley and Delta would construct and repair very low perimeter dams of soil to trap water for infiltration into the cropping area (Figure #7). One crop per year was harvested after growing during the fall and winter seasons following annual flooding. Beginning in the early 19th century, a series of low diversion dams (barrages) on the main stem of the Nile in Egypt were constructed, feeding into irrigation canals to permit summer crops to be grown during the low stage levels of the river prior to flooding. By the middle of the 19th century, the main summer crop was cotton, which then became the major agricultural export product from Egypt. Early in the 20th century, the first of a series of dam construction projects at Aswan in southern Egypt was begun. These water storage projects evolved by continued raising of the dam height until the mid 1930's when a maximum of about two months of "average" discharge by the Nile could be impounded for irrigation water deliveries to summer crops. By about the middle of the 20th century, the beginning of a system of drainage tiles under the soils of each field in the Nile Delta was established, followed by excavation of a network of drainage canals and eventually large diesel powered pumps to transfer drainage water into the Mediterranean. International aid efforts from the Netherlands, other countries and the World Bank over a number of decades have provided much effective help to Egypt on drainage issues in the Nile Delta.
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 (Figure #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 (Figure #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 (Figure #9A) for the period prior to construction of the High Dam (1912-
- to that after discharge regulation was completed (Figure #9B). Note that the total amount of Nile water passing into the populated area of Egypt immediately after completion of the High
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.
Most of the water of the Nile River released from the High Dam in upper (southern) Egypt is used for irrigation of crops. Although irrigation has been a major activity in Egypt for more than 5000 years, the intensity involved today has only been a feature of the last five decades, following completion of the High Dam at Aswan during the middle 1960's. The Ministries of Irrigation and Agriculture in Egypt have encouraged increases in food production to occur as rapidly as possible, but there are some major natural resource issues concerning available water and land suitable for agriculture which make that quite difficult to do.
The largest area of crops annually planted in Egypt (about 12% of total crop area) is a clover (Figure #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.
The production of food crops per unit area of agricultural land in Egypt is currently among the highest in the world for a large range of crops. This situation exists in spite of a farming system that relies on relatively little use of fossil fuels and mechanical devices to displace human and animal labor, compared to agricultural practices in most industrial countries. We can get some appreciation of the high yield of food production per unit of crop land in Egypt by comparing average yields of rice with those of a number of other countries. Dividing countries with populations greater than 10 million (1982) into three groups, based on GNP per capita, Egypt had the highest production of rice per unit area of land of any country in the lower income category (< 1000 $US per capita), equal to more than 5 tons of rice per hectare (one hectare = an area equal to that of a square 100 meters on each side, or about 2.5 times that of an acre in the English unit system). Egypt had average annual rice production per unit of crop land greater than
that of China, and almost as great as that of Japan, which has the highest production costs for rice of any major country in the world.
Wheat production per unit area in Egypt is also quite high (Figure #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
- 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 (Figure #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.
The history of population growth in Egypt for the past two hundred years is similar to that for many other developing countries. Since the end of World War II, the population has approximately tripled from less than 20 million to more than 60 million (Figure #14). When Napoleon first arrived in Egypt at the beginning of the 19th century, the total population of the country was only about 3 million, about 4% of the current population. This large growth in total population is especially critical in a country where boundaries between rich agricultural crop lands and the surrounding desert are so dramatic. There is no plausible area for major expansion of cropland area into the desert, despite valiant attempts to push food production into such areas over several decades.
If we consider the history of population in Egypt over longer time scales, the trends over the past two centuries are even more dramatic (Figure #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
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 21st 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.
Updated January 11, 2007
