TAU Trends in Research June 1998

From Ecuador to Jerusalem, El Niño Takes its Toll

A map of the world showing the recent divergence of the surface temperature on the oceans from their usual average values/ Values range from 4^oC warmer than normal (red) to 4^oC cooler than normal (purple). The upwelling of warm water off the coast of Ecuador and Peru is typical of an El Niño Southern Oscillation (ENSO) event.

Dr. Colin Price and Dr. Pinhas Alpert of the TAU Department of Geophysics and Planetary Sciences, and Dr. Lewis Stone and Amit Huppert of the TAU Department of Zoology have found convincing evidence that the ENSO phenomenon also affects Israeli weather, economics and life. They have been studying rainfall in the watershed region of Lake Kinneret, the source of a third of Israel's total water supply and half of its drinking water. Monthly rainfall data, the flow of the Jordan River into the lake, the daily lake water level and snowfall data (from Jerusalem and Mt. Canaan) were compared with the monthly sea surface temperature in the eastern tropical Pacific, a third of the world away.

Eight of the last ten ENSO's were associated with wetter than average winters in northern Israel. Snowfall, water flow in the Jordan and subsequent water levels in the Sea of Galilee were also higher. However, the impact of an ENSO event on Israeli weather is not always proportional to its intensity; and other global events, such as the June 1991 eruption of Mount Pinatubo in the Philippines, can also influence Israeli weather. In all, the TAU researchers found that ENSO events account for only 36% of the variability of local rainfall. Similar levels of correlation exist between ENSO events and African droughts.

What global meteorological mechanisms link Peruvian fisherman and Israeli farmers? No one is sure, although changes in the subtropical jet stream or, more likely, the polar jet stream have both been suggested.

However, the TAU researchers have found surprising evidence that this particular long-distance connection is a recent one. The observed correlations are statistically significant for only the last 20-25 years (at the 99% and 95% level respectively).

ENSO-related snow storms battered Jerusalem this year - one only days after a desert duststorm - breaking trees, halting traffic and providing residents with a temporary winter wonderland.

Similar results have recently been reported for Spain, suggesting that the Mediterranean's participation in global climatic events has undergone a largely unnoticed change in the very recent past - more recent than TAU's move to Ramat Aviv in 1964. The global mechanisms underlying the world's weather seem far more plastic than we usually realize.

For further information please contact:
Re:  Meteorology -

1. Dr. Colin Price

   Tel.:	(00972) 3 / 640 6029
   Fax. :	(00972) 3 / 640 9282
   E-Mail:	cprice@flash.tau.ac.il

2. Prof. Pinhas Alpert

   Tel. :	(00972) 3 / 640 7380
   Fax. :	(00972) 3 / 640 9282
   E-Mail:	pinhas@cyclone.tau.ac.il

Re:	Ecology - Dr. Lewis Stone
	Tel.:	(00972) 3 / 640 9806
	Fax.:	(00972) 3 / 640 9403
	E-Mail:	lewi@lanina.tau.ac.il

Department of  Zoology
The George S. Wise Faculty of Life Sciences
Tel Aviv University
P.O.B. 39040
Tel Aviv 69978
Israel