16 - 22 September 1999
Issue No. 447
|Published in Cairo by AL-AHRAM established in 1875|
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Solving the riddle of the NileBy Rushdi Said *
If this year's Nile flood is as high as predicted it will be the fourth time in as many years that the flood has exceeded its normal levels.
This year's flood, however, is a little different from the previous three, for instead of coming from the Ethiopian Highlands most of the water this year comes from the Sahel region where intense rainfall occurred over Khartoum, western Sudan and Nubia as well as the lower reaches of the Atbara River.
The rains that fell over Khartoum and western Sudan were so intense that they resulted in loss of life and destruction of property. They activated many of the dry wadis of western Sudan and Nubia, which came roaring into the cities on the west bank of the Nile. The waters carried by Wadi Abu Anga, which opens up in the city of Um Dorman, rose more than a metre in height in less than an hour. This torrent of water split the city before rumbling into Khartoum North on the other side of the river.
The waters that drained into the White Nile by the activated dry wadis of western Sudan caused many fields to be submerged and led to calls for the opening of the Gebel Aulia Dam to help drain the water trapped behind.
But while the rains were heavy along the Sahel belt, from the plains of Kurdofan in the west to the plains of Kassala across the river in the east, the Ethiopian Highland itself remained drier than usual, forcing the governments of Ethiopia and Kenya to appeal for help from international relief agencies and donor countries.
The distribution of rains this year is similar to that of 1998. In that year most rain also fell on Khartoum, Nubia and the Atbara basin while lesser rains fell on the Blue Nile basin, causing the highest flood of the twentieth century.
Top to bottom: Where is the water? A village woman expresses her despair; a despondent village ponders the reasons behind their plight; a local woman contemplates the Aswan High Dam; Fahmi Tawadros explains the national significance of the Dam; Khazzan Aswan: early attempts to manage waters with a will of their own
This exceptional pattern of rain distribution is associated with unusual weather phenomena affecting many parts of the world. This summer has seen exceptionally high floods and great droughts across the world, resulting in enormous material damage. While in China and the Philippines floods have been high, the eastern coast of the United States experienced drought conditions that forced many eastern states to enforce restrictions on the use of water resulting in grave losses of farm produce.
The past winter also saw severe drought conditions in the Middle East. The levels of the Euphrates, Tigris, Jordan and Orontes rivers were all low. Farmers were once more affected negatively, and great material and financial losses were incurred by the governments and peoples of Iraq, Syria, Palestine, Israel and Jordan.
The drought that hit the Middle East and the eastern coast of the US was the severest this century. But so were the high floods of the Far East.
The underlying causes of such unusual weather phenomena remain controversial and the subject of intensive study. Most authors, though, claim that these phenomena, which occur periodically, are due to changes in the movement of the water masses of the great oceans of the world.
The Pacific Ocean covers a large part of the surface area of the earth. The movement of its water masses produces the currents that influence the gradients of atmospheric pressure which in turn determine wind movements and the amount of rain that falls over many parts of the world. The movement of the water masses of the Pacific Ocean is governed by the trade winds, which in ordinary times push the mass of warm surface warm water off the coasts of Chile and Peru. This causes the upwelling of cooler water to replace the surface water pushed away from the coasts, water that carries with it the nutrients that attract fish and make for a good fishing season.
A diversion of this regular pattern happens every few years when the trade winds become too weak to push the warm surface warm water away from the South American coast. The surface water stays in place and no upwelling of the bottom waters takes place. Weather patterns change as the warm surface waters cause atmospheric pressure to be reduced. This phenomenon is known as El-Nino.
A reverse phenomenon, which we are witnessing now, occurs every few years during the summer season when the surface water of the South and North American coastal areas of the Pacific Ocean fails to become warm. This phenomenon is called El-Nina.
Both phenomena affect the global weather. The Far East, for example, suffers drought during the El-Nino years as the warm current that carries the rain to this region is prevented from reaching its coasts. Ordinarily that current reaches these coasts in summer time and causes the rains. During the El-Nina years the rains become exceptionally strong because the rain-carrying current is forced to stay for a longer period of time, as is happening this year.
I have already shown in my book on the River Nile (Oxford, 1993) that the El-Nino and El-Nina phenomena affect the quantity of water that is carried by the Nile. The El-Nina seems to have a greater effect on the amount of the waters of the flood, which occurs during the summer. When it is in effect, the current of surface warm waters stays along the shores of the Atlantic coast furnishing the monsoons with greater amounts of water vapour and allowing for heavier and more sustained rains. During the past hundred years I have counted 20 high floods that coincided with the years of El-Nina. On the other hand I have counted 26 years of low floods that coincided with the years of El-Nino.
In a region that lies in the midst of the greatest desert belt of the world and where water is a rare commodity, the study of the forces that affect the availability of that commodity becomes extremely important. The expected increase in demand for water in the Middle East and in the African Sahel as a result of the growth of populations and the changing patterns of water utilisation will make water availability one of the most urgent problems in the near future. It seems that the phenomena of El-Nino and El-Nina, which originate many thousands of kilometres away, have world-wide effects on the weather and an impact on the amount of water that the River Nile carries. In their study may lie the key to solving the riddle of predicting the condition of the Nile, a riddle that has occupied the minds of Egyptians since time immemorial.
* The writer is the former head of Egypt's Geological Survey.