Climate PDF Print E-mail
Written by Stephen Langfur
 
  

The land knows basically two seasons, the dry and the sometimes rainy. The dry season extends roughly from mid-April until mid-October. It begins when the sun "shifts" toward the earth's northern tropic. "This results in a northward movement of the warm upper air mass of the equatorial region" (Baly,  p. 44).Compared to this upper air mass, the air below is cool (though still hot enough for the tourist!). Warm air, of course, tends to rise until checked by gravity. Therefore, in a situation where a mass of warm air is sitting over a mass of cooler air, the latter cannot rise. That is the situation over the Mediterranean in the summer, and the result is remarkably stable weather, especially from June 15 until September 15, when the sky seems interminably blue (and the visibility interminably mediocre). 

It is no coincidence that the three Israelite pilgrimage festivals fall in the dry season, when the roads aren't muddy: Pesach (Passover) at the beginning, Shavuot (Weeks or Pentecost) seven weeks later, and Sukkoth (Tabernacles) before the first rains.

Air does move steadily in from the Mediterranean during the summer, but it is not moist enough to bring rain. In the cool nights, however, the moisture condenses as dew, swelling the grapes. On the coast south of Gaza there are 250 dew nights per year, compared to 138 in Haifa. The Bible abounds with references to the blessing of the dew.

The rainy season can start any day after September 15. The sun "shifts" to the southern tropic and the upper air mass is chilled, allowing the lower air to rise. The jet stream, sweeping powerfully from west to east, had shifted to the north for the summer, but now it moves to the south of the Alpine-Zagros-Himalayan mountain ranges. Baly (op. cit., p. 47) writes: "A strong high pressure system develops over the bitterly cold Russian-Siberian land mass and somewhat lesser ones over Arabia and the Sahara." (High pressure systems, be it noted, tend to block incoming storms or push them into other regions.) Baly continues: "Between the two lies a deep trough of low pressure along the Mediterranean and the Persian Gulf. All this makes for great instability in the atmosphere."

Cyclonic storms, bearing damp air from the Atlantic, sweep through the Mediterranean trough. Various factors rejuvenate them: the warm water of the sea; the meeting with warm air from Africa and cooler air from Europe; the jet stream overhead. The storms take between four and six days to traverse the length of the Mediterranean, and when they strike the Levantine coast, they drop rain for about three days. In a good year such storms arrive about once a week, but there is no regularity about them.

Jerusalem and London get the same amount of rain: 560 mm. (22.4 inches), but the former receives it all within 50 days, whereas the latter has it spread over 168. The Holy Land is so mountainous, moreover, and the descent into the Dead Sea Transform so steep, that much of the water from the rainfall is lost. Today the average Israeli has 380 cubic meters of water available per year (and uses 330). The average Palestinian in the West Bank has 165, in Gaza even less. By comparison, the average US citizen has 10,000 cubic meters, the average Turk or Iraqi about 4500 (Source for these figures).

It was enough water in antiquity, nonetheless, to make this small country the land bridge between Europe, Asia and Africa - and to provide the local inhabitants with grain, wine and oil.