Page 82 - Arabian Studies (V)

72 Arabian Studies V

sand deposits in the form of migrating isolated barchan sand dunes
have progressively coalesced to form an extensive duncficld in the
!
Khawr al-‘Udayd region of south east Qatar. In addition, many of
the depressions of southern Qatar have been infilled with aeolian
sand deposits upon which vegetation has become firmly estab­
lished. Much of the storm-water run-off terminating in these sand-
filled depressions is thus rapidly absorbed and intercepted by the
vegetation and little water therefore percolates to groundwater. In
'I contrast, the depressions of northern Qatar are generally free of
aeolian sand deposits, and hence vegetation, and the bare soil
surface offers a maximum infiltration opportunity. These differ­
ences in geomorphology, distribution of aeolian sand and
vegetation are considered to have played a significant role in the
original accumulation of freshwater in northern Qatar where
percolating recharge has increased the regional permeability and
allowed a considerable volume of freshwater to accumulate as a
‘floating lens’ upon more saline groundwater.

I 3. Climate and rainfall
Qatar lies wholly within a torrid sub-region of the northern desert
belt, characterised by a scanty rainfall of about 50 mm. per annum,
high temperatures, hot dry summer winds and, because of its
geographical position within the Arabian Gulf, experiences a high
relative humidity for the greater part of the year (Pike et al., 1975).
Climatological data show that the climate of Qatar, even under
stable conditions, varies from coastal to inland sites over short
distances and the contrast is further heightened in the artificial i
oases of established farms where the presence of water, crops and
trees has had the effect of creating a marked micro-climate. In
these oases temperatures are lower, humidity higher, wind speeds
lower and evapo-transpiration is about 25 per cent less than at
1 adjacent open desert sites. An analysis of data shows that the year i
may be divided into four distinctive climatic seasons of varying
length which bear only a general relationship to the main climate
seasons of the sub-tropical zone. Period 1 (November—mid-
February) constitutes the main growing season when temperatures
range from a daily maximum of 30°C to a minum of 7°C; Period II
(mid-February—mid-May) is marked by rapidly rising tempera­
tures and increased windspeed; Period III (mid-May—July) is
characterised by very high daily maximum temperatures of above
42°C and accompanied by strong dessicating north-westerly winds;
Period IV (August—October) is marked by the sometimes sudden
onset of greatly increased relative humidity and a decrease in wind