IS THE PATTERN OF RAINFALL IN ISRAEL AFFECTED BY THE ASWAN HIGH DAM ?

URI BATZ

Israel Meteorological Service

From the end of the 1960's, changes took place in the spatial distribution and quantity of precipitation in Israel, which are difficult to attribute solely to random fluctuations. A downwards trend in the quantity of precipitation in the northern part of Israel, whereas an upwards trend in the quantity of precipitation in the central and southern part of Israel began to appear (Steinberger and Ya'ari-Gazit, 1992).

Parallel to these changes the Aswan High Dam project was completed in Egypt. Its first stage was completed in 1964 and the dam was fully operational in 1970 , and as such clearly serves as an excellent example in its effect upon the ecological balance in the area .

The key question which must be posed is : has the operation of the Aswan Dam affected the Israeli rainfall pattern?

The dam has severely reduced the flow of the river Nile. Before its construction , an average of 40 billion cubic meters of water flowed to the Mediterranean each year, whereas after it was completed the flow was reduced to 3 billion cubic meters (Wadie,1984;Sharf El Din, 1977).

These alterations in flow have also affected the Mediterranean . Oceanographic studies have shown that the thermal and saline levels in the south-eastern region of the Mediterranean have changed.(Hecht, 1992; Wadie,1984; Gerge,1976).

It is reasonable to suggest that the changes in the thermal structure of the sea have led to alteration in the positions of the winter pressure systems in its southern region. In turn , this situation has influenced the amount and pattern of rainfall in Israel, which also was affected by the global climate (Cohen,1991;Steinberger and Ya'ari-Gazit,1992).

We are faced with an overall picture of rainfall completely different from which we have been accustomed to seeing in the past. This picture is highly significant and to my opinion holds critical implications from the hydrological aspect and for the balance of water resources in Israel. This means that there is a higher probability of winters in which there will be less rain in the north than the average , and since Israel's main water sources are situated in the north, there is a possibility of damage being caused to the balance of water resources in Israel.

This paper is about the range of issues , climatic and oceanographic , influencing the rainfall in Israel ,pre and post the construction of the Aswan High Dam in Egypt.

image1
Satellite thermal analysis, shows warm and cold water in the eastern Mediterranean .the warm water are in turquoise and the colder are in gray.

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Appendix

For a better orientation I am including a satellite image2
of Israel with some details about the places I mentioned in the paper. The research was completed in 1995 and since then the rainfall trend between the years 1995-1998 was as I found in my work except the rainfall amount in the year 1997\1998 when the central part of Israel received 90-95% rainfall ,from the average, and the northern part of Israel( Zefat is the station which represents the northern mountains) received 110-120% rainfall from the average which is opposed to my theory. I assume it happened due to El-Ninio phenomena, which caused a slight rise in the sea surface temperature (sst) in the East Mediterranean.
 

PLACES	Long.E	Lat.N	Elevation in meters	Yearly average Rainfall in mm
ZEFAT	3530	3258	930	718
JERUSALEM	3513	3147	810	554
NAHARIYA	3506	3301	10	640
GAZA	3428	3130	7	410