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Saudi Arabia
Climate
With the exception of the province of Asir with its towns of
Jizan on the western coast and Najran, Saudi Arabia has a desert
climate characterized by extreme heat during the day, an abrupt
drop in temperature at night, and slight, erratic rainfall. Because
of the influence of a subtropical high-pressure system and the
many fluctuations in elevation, there is considerable variation
in temperature and humidity. The two main extremes in climate
are felt between the coastal lands and the interior.
Along the coastal regions of the Red Sea and the Persian Gulf,
the desert temperature is moderated by the proximity of these
large bodies of water. Temperatures seldom rise above 38°
C, but the relative humidity is usually more than 85 percent and
frequently 100 percent for extended periods. This combination
produces a hot mist during the day and a warm fog at night. Prevailing
winds are from the north, and, when they blow, coastal areas become
bearable in the summer and even pleasant in winter. A southerly
wind is accompanied invariably by an increase in temperature and
humidity and by a particular kind of storm known in the gulf area
as a kauf. In late spring and early summer, a strong
northwesterly wind, the shamal, blows; it is particularly
severe in eastern Arabia and continues for almost three months.
The shamal produces sandstorms and dust storms that can
decrease visibility to a few meters.
A uniform climate prevails in Najd, Al Qasim Province, and the
great deserts. The average summer temperature is 45° C, but
readings of up to 54° C are common. The heat becomes intense
shortly after sunrise and lasts until sunset, followed by comparatively
cool nights. In the winter, the temperature seldom drops below
0° C, but the almost total absence of humidity and the high
wind-chill factor make a bitterly cold atmosphere. In the spring
and autumn, temperatures average 29° C.
The region of Asir is subject to Indian Ocean monsoons, usually
occurring between October and March. An average of 300 millimeters
of rainfall occurs during this period--60 percent of the annual
total. Additionally, in Asir and the southern Hijaz condensation
caused by the higher mountain slopes contributes to the total
rainfall.
For the rest of the country, rainfall is low and erratic. The
entire year's rainfall may consist of one or two torrential outbursts
that flood the wadis and then rapidly disappear into the soil
to be trapped above the layers of impervious rock. This is sufficient,
however, to sustain forage growth. Although the average rainfall
is 100 millimeters per year, whole regions may not experience
rainfall for several years. When such droughts occur, as they
did in the north in 1957 and 1958, affected areas may become incapable
of sustaining either livestock or agriculture.
Data as of December 1992
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