U.A.E. lies on the southern shore of the Arabian Gulf lies directly on the
tropic of Cancer. The Arabian Gulf it is surrounded by land, and has an arid,
sub tropical climate that is continental in character and consequently has
marked seasonal fluctuations in temperature (Purser and Seibold, 1973). This,
coupled with the narrow Straits of Hormuz inhibiting the exchange of marine
water, creates conditions in which the local sea water temperature and salinity
vary widely. The air temperatures in the summer commonly reach 45
50°C, or in the winter may be as low as 0°C (Purser and
The combined effect of strong winds, high temperature
and low rainfall results in significant evaporation and high salinities (Purser
and Seibold, 1973) and the precipitation of the evaporite minerals gypsum and
anhydrite in the coastal sabkha settings accompanied by a lack of natural
vegetation in these regions.
Winds blow dominantly from the northwest throughout
the year (Kinsman, 1964) and this continuously drives the dews and associated
humid air landward. The strongest winds are the northwest gale force
"shamals" which occur during the winter. When these winds coincide
with spring tides they cause flooding of large parts of the coastal plain. As with the hurricanes of the
Caribbean and Florida (Pray, 1966), the shamals carry sediment landward from
the frontal edges of the carbonate coastal shoals onto the
supratidal flat, breaching and flattening coastal dunes and uprooting the
vegetation that colonize them; they also initiate intertidal spits and beach
ridges at the top of the intertidal flat on which the coastal dunes develop.
This dominant wind direction has been constant through the Holocene and
Quaternary, and the Pleistocene "miliolite" dunes exhibit a cross
bedding that invariably dips southeast.
The average rainfall of the U.A.E. is less than 50 mm
(Evans et al, 1969) and consequently vegetation is restricted. Rainfall
recorded at Tarif from 1958 to 1964 is shown in Table 1.
Table 1. U.A.E. Coast
These rains fall in autumn, winter or spring.
Although infrequent, they may be torrential. The rain locally has a short term
effect on the vegetation but although producing ephemeral changes in the
evaporite mineralogy, this has little effect on the sediments and groundwater
(Butler, 1965). Fluvial input is low in the Arabian Gulf and is mainly confined
to the Iranian side of the Gulf where the Zagros Mountains are a source of
alluvial sediments. Fluvial input is significant at the Shatt al Arab where
most of the fluvial sediment load accumulates in the marshes of Iraq (Berry et
al., 1970). On the Arabian side of the Gulf, fluvial input does not occur, so
the depositional setting favors little vegitation and the accumulation of almost pure carbonate (Purser and Seibold,
Evaporation rates in the southern Arabian Gulf were
estimated by Privett (1959) to be as much as 124 cm per annum. High summer
salinities recorded by Sugden (1963) for part of the southern Gulf suggest that
evaporation is greatest in summer, especially in restricted lagoons.
Brines collected by Butler (1965) from the ground
waters of the sabkha both before and after storm induced marine flooding showed
no appreciable difference in the concentrations of the various salts. There
was, however, some effect on the evaporites. halite was washed from the surface
sediments, while anhydrite on the surface above the intertidal zone was eroded.
From the above description it is clear, with the
exception of diurnal dew, the climate and surface hydrology does not favor the
growth of lush vegetation.