Harvesting the Skies of Egypt: An Option to Recover the Evaporation Losses from the Aswan High Dam Reservoir

Abstract

The Aswan High Dam Reservoir (AHDR) is one of the largest man-made reservoirs with a surface area of 6,000 km². It was built in the aridest zone of Egypt and Sudan. Evaporation losses range from 5 to 10 mm/m²/day throughout the year and average 7.4 mm/m²/day leading to an estimated loss of 16 km³ or 20% of the annual consumption of water by Egypt for farming, industrial, and domestic applications.

These losses cannot be prevented and are difficult to reduce. Schemes to compensate for the evaporation, namely, weather modification and water harvesting from the air, are examined in this chapter. Evaporation losses are transported at low levels of a few hundred meters but also at heights of 1,500–4,000 m as there are different patterns of lower and upper winds.

For the lower levels, there are two important technologies that have grown in other countries to extract water vapor from the air: fog harvesting and dew harvesting. The success of these technologies is very much dependent on the geography of the site and its climate. Efforts to utilize nocturnal radiation for refrigeration and natural ice making at night are not a recent phenomenon; the Ancient Egyptians and Ancient Persians were champions of nocturnal refrigeration where the intense cooling radiation to a black sky was used to freeze water and produce natural ice. This technology can be adapted in an Egyptian context. Fog collectors must be capable of resisting the strong “khamsin” windstorms between March and June.

Egypt has an interesting pattern of inversion of temperature between night and day. This leads to the formation of dew and fog and low clouds particularly over the Delta and Cairo during certain periods of the year and just for few hours to few days but also to vigorous vertical currents rising to 4,000 m and transporting evaporated water.

The direction of the winds over the Aswan High Dam Reservoir tends to blow from the north and northwest. This would suggest that water lost by evaporation tends to flow along the axis of the reservoir south toward Upper Nubia or Northern Sudan and southeast toward the Egyptian Eastern Desert, the Halayeb region, and the Red Sea coast. The Hadley cell pattern over the Earth forces the water lost by evaporation at the AHD Reservoir back to the equator. Coriolis forces due to the rotation of the Earth curb this flow slightly toward the east. While the Grand Ethiopian Renaissance Dam (GERD) will deprive the AHD Reservoir of waters, the AHD Reservoir will continue to feed back the sources of the White Nile and the Blue Nile with water by evaporation. The governments of Egypt and Sudan should embark on weather modification to capture these losses. The clouds are overcast at 5–25% over Lake Nubia and Lake Nasser and will require a carefully planned approach.

The technology of weather modification can also be tested on the northern coast of Egypt from Salum to Rafah and certain parts of the Delta where annual precipitation ranges from 50 to 200 mm/year. The Ancient Egyptians, the Greek, and Roman rulers had developed in the past a complex system of deep wells and water storage schemes for storing rainwater that should be revived in parallel to weather modification schemes.

Cloud formation over the AHDR is at its peak during the flood season of July and August, while it is at a minimum over the north coast of Egypt. This opens an opportunity to maximize utilization of aircraft all year round with an emphasis on the north coast in the winter and on Lake Nasser in the summer. Weather modifications must be viewed as a carefully planned project. The conditions favor high-altitude cloud seeding at 4000 m to avoid the errors and pitfalls of low-altitude failures.

Egypt and Sudan do not have currently a program for weather modification or cloud seeding. This chapter is, therefore, an attempt to open the discussion on the merits of this technology.