"The great desert region of Persia," writes Le Strange (Lands of the Eastern Caliphate, 1905), "stretches right across the high plateau of Iran going from north-west to south-east, and dividing the fertile provinces of the land into two groups; for the desert is continuous, from the southern base of the Elburz mountains, which to the north overlook the Caspian, to the arid ranges of Makran, which border the Persian Gulf. Thus it measures nearly 800 miles in length, but in breadth varies considerably; for in shape this immense area of drought is somewhat like an hour-glass, with a narrow neck, measuring only some Too miles across, divid ing Kerman from Seistan, while both north and south of this the breadth expands and in places reaches to over 20o miles. At the present day the desert, as a whole, is known as the Lilt or Dasht i-Lfit ; the saline swamps and the dry salt area being more par ticularly known as the Dasht-i-Kavir, the term Kavir being also occasionally applied to the desert as a whole." Climate.-In winter the prevailing winds are north-easterly, but in the north are interrupted three or four times a month by the eastward passage of depressions from the Mediterranean, bringing westerly winds and moderate rainfall. In summer a strong dust-laden northerly wind blows almost unceasingly for about four months. This wind is known as the Shamal; in June it often carries dust far out into the Persian Gulf, but in July the south-west monsoon sets in along the coast, and the northerly winds are mostly limited to the interior. Seistan, in Eastern Persia, is known as "The Land of the Winds," and is especially noted for the "Wind of 120 days" which sets in at the end of May and blows from a little west of north until the end of September, reaching a velocity of over 7o miles an hour.
The mean annual temperature reaches 8o° F over the coast of Mekran and is 75° F at Bushire, but in the interior it is consid erably lower, owing to the greater altitude and the cold winds of winter. The annual variation of temperature is very great in the north, where July is more than 40° F warmer than January, but diminishes rapidly southward to on the south coast. The highlands have very severe winters; thus Tehran, at a height of 4,000 feet, has a January mean of 35° F, while extreme tempera tures below o° F have been recorded in Isfahan. The most pleasant season on the highlands is spring, with a moderate tern perature and ground still moist from the winter rain and snow. In autumn, though the temperature is moderate, the air is dry and dusty. Summer is everywhere very hot, the mean temperature in July and August exceeding 8o° F over almost the whole country. The day temperature is very high, but the nights are cool. Maxi mum temperatures exceeding o° F have occurred at elevations of 5,00o feet, and even at Dehbrid (8,000 feet) 93° F has been recorded. On the coast the nights are very warm and oppressive.
The rainfall is small everywhere except on the Elburz moun tains, which receive a heavy fall in winter owing to depressions which originate over the Caspian. At Resht, the annual average is
56 inches, but the amount decreases rapidly eastwards to less than 20 inches over the eastern end of the range. Over the plateau south of the mountains the annual total is about 9 inches in the north, but decreases southward and especially south-eastward, being only two inches a year at Husseinabad and Seistan. At the head of the Persian Gulf the rainfall is somewhat greater, slightly over ten inches, but the Mekran coast has again a very small amount, generally about 5 inches. The rainfall is almost entirely limited to the months of October to May inclusive and is heaviest from December to March, any one of which may be the wettest month. The rainfall is very spasmodic, and more than half the annual total may fall in a single day; thus 5.53 inches fell in one day at Bushire, and falls of more than an inch have been recorded at Husseinabad and Seistan. In consequence of this variability, disastrous droughts sometimes occur. Thunderstorms are experi enced on a few days each year. Taking Persia as a whole the snowfall may be said to be very variable and uncertain. In the maritime areas a fall of snow is naturally a very rare occurrence. In the highlands, on the other hand, country over 4,00o feet in alti tude is liable in any winter to be under snow for days and not infrequently weeks together, between December and April. Dur ing such periods of severe weather the passes leading from the plains to the plateau become closed to wheeled traffic, while dur ing the ensuing thaw they are little less difficult for pack-animals. During the World War, when British troops were located along the Baghdad-Enzeli route and the line of communications had nec essarily to be kept open, great labour was involved in keeping the track clear of snowdrifts, especially on either side of the Sultan Bulagh pass between Hamadan and Kazvin. An interesting account of the migration of a Bakhtiari tribe, from the plains of Arabistan to their summer quarters in the highlands near Isfahan under severe snow conditions, is to be found in Grass by C. Merian Cooper (1925).
Flora.—In the provinces of Gilan, Mazandaran and Astarabad on the Caspian, from the shore to an altitude of about 3,00o ft. on the northern slopes of the great mountain range which separates those provinces from the highlands of Persia, the flora is similar to that of Grisebach's "mediterranean region." At higher altitudes many forms of a more northern flora appear. As we approach inner Persia the flora rapidly gives place to "steppe vegetation" in the plains, while the mediterranean flora predominates in the hills. The steppe vegetation extends in the south to the outer range of the hills which separate inner Persia from the Persian Gulf and the Indian Ocean. Beyond this outer range and along the shore of the sea the flora is that of the "Sahara region," which extends eastwards to Sind.