June to September
brings a fairly abundant rainfall to the Yemen highlands, though the
Tehama remains almost entirely rainless. The rainfall is heaviest
along the western fringe of the plateau, and penetrates inland in
decreasing quantity over a zone which perhaps extends to 100 m. in
width. In good seasons it is sufficient for the cultivation of the
summer crop of millet, and for the supply of the perennial streams and
springs, on which the irrigation of the winter crops of wheat and
barley depend. The amount measured at Dhala at the extreme south of
the plateau at an elevation of 4800 ft. was in 1902 as follows:--June,
4.0 in.; July, 5.5; August, 5.8; September, 1.9. Only slight showers
were recorded in the other months of the year. At higher elevations
the rainfall is no doubt heavier; Manzoni mentions that at Sana there
was constant rain throughout August and September 1878, and that the
thermometer during August did not reach 65 deg. In the Tehama
occasional showers fall during the winter months; at Aden the average
rainfall for the year is 2.97 in., but during 1904 only 0.5 in. was
recorded. Snow falls on the Harra and on the Tehama range in northern
Arabia, and Nolde records a fall of snow which lay on the Nafud on the
1st of February 1893. It also falls on J. Akhdar in Oman, but is very
rarely known on the Yemen mountains, probably because the
precipitation during the winter months is so slight.

The prevailing winds in northern Arabia as far as is known are from
the west; along the southern coast they are from the east; at Sana
there is generally a light breeze from the north-north-west from 9 to
11 A.M., from noon till 4 P.M. a steady and often strong wind blows
from the south-south-east, which dies away later. The climate is
extremely dry, but this is compensated for by the heavy mists which
sweep up from the plains during the rainless months and exercise a
most beneficial effect in the coffee-growing districts. This
phenomenon is known as the sukhemani or amama. In the morning the
Tehama, as seen from the mountain tops, appears buried in a sea of
white cloud; towards noon the clouds drift up the mountain slopes and
cover the summits with wreaths of light mist charged with moisture
which condenses on the trees and vegetation; in the afternoon they
disappear, and the evenings are generally clear and still.

_Fauna._--The wild animals of A