Page:Africa by Élisée Reclus, Volume 1.djvu/189

 lie within the tropics, the sun's rays maintain their intensity throughout the year, the discrepancies between winter and summer being very slight, and due mainly to the purity of the air and density of the clouds. As in the West Indies and in all countries subject to regular monsoons, the Abyssinian year is regulated by the appearance and disappearance of the rains.

The rainy season varies in time and duration according to the height, latitude, and position of the various provinces. Some regions have even two rainy seasons, being lands of transition belonging at once to two meteorological domains. The southern Abyssinian uplands have two winters, the first commencing in July, when the sun is nearly vertical above the soil, and ending in September ; the second and shorter falling in January, February, or March, when the belt of clouds formed at the zone of contact between the trade- winds and polar currents is deflected south- wards. In the central region the winter, or azmara, commences usually in April, continuing, with a few interruptions, till the end of September; but at the north- west base of the mountains, in the Bogos, Galabat, Gcdaref, and Senaar provinces, this rainy season is broken into two, one beginning in April or May, the other, accompanied by tremendous downpours, lasting throughout the months of July, August, and September. The rains, brought by the wind blowing from the Red Sea or Indian Ocean, fall nearly always in the afternoon, accompanied by tempests, but soon clear off, leaving the sky unclouded during the night and following morning. On the eastern slope of the mountains, however, the seasons are reversed, the rains brought by the north wind falling in winter, which lasts from November to March.

The African coast of the Red Sea lies within the zone of the Mediterranean winter rains, whilst those of Arabia, the interior of Egypt, and Upper Abyssinia belong to a different climatic system. Certain mountains situated on the boundary of the two zones are alternately beaten by winter and summer rains, and the Abyssinian shepherds have but to go round the mountain to find, according to the season, the herbage necessary for their flocks or land ready for culture. During this period the air enveloping the lowland plains is excessively damp, the hygrometer never indicating a less proportion than 60 per cent., while the air of the plateaux is, on the contrary, usually dry.

In the districts where the annual rainfall has been roughly estimated, it is found to vary from two to three inches yearly. But the discrepancy must be much greater in some upland valleys, where the rainclouds are driven together by the winds. Here hailstorms are very frequent. Floodings are known to be extremely dangerous in valleys surmounted by precipitous and barren rocks; but on the eastern ledges of the Abyssinian border ranges these sudden deluges rushing through steeply inclined watercourses are even more dangerous than elsewhere. During the rainy season all communication ceases between the plateaux, which are divided one from the other by deep kwallas. In the plains of Samhar the caravans, journeying through sand, saline clays, and lavas, are occasionally stopped by the intolerable heat reflected from the earth or rocks, or else by the sandy whirlwinds of the kharif, or columns of red sand sweeping over the desert.