IIIFカラー高解像度
国立情報学研究所 - ディジタル・シルクロード・プロジェクト
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| IIIFカラー高解像度 |
| Overland to India : vol.2 | |
| インドへの陸路 : vol.2 |
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引用情報
CHAP. L CLIMATIC CHANGES IN PERSIA 209
the surface of the sea in the time of Istakri, or in the years 915 to 921, lay 30.45 feet higher than in 1847. Still more decisive is the fact that remains of buildings are found on the eastern, southern, and western shores below the present surface of the sea. On the east coast a caravanserai, and at Resht several houses stand under water. Before Baku there is likewise a serai, of which only a tower rises above the surface. On investigation it has been ascertained that it was built in the twelfth century. The water-level was then 16 feet below its height in 1852. Particular attention should be paid to this fact, that the Caspian Sea was much lower 750 years ago than it is now, for it proves more clearly than anything else that the desiccation of the climate of Central Asia and of the lakes by no means follows a regular curve. Afterwards, a marked rise set in, attaining in 1306-7 its maximum of 35.1 feet above the level of 1852. In order to render the different values com- parable with one another Bruckner refers them to a common standard (B,) and compiles the following table :-
t Years 915-921 . . + 28.9 feet.
t Twelfth century . — 13.8 „
Years 1306-7 . . + 36.7 „
„ 1638 . + 16.1 „
„ 1715-20 . • + 1.0 „
Then follows a period of comparatively high water, I then a period of fall and another of rise.
Then Bruckner proceeds to show that the water-level in the Caspian Sea depends on the precipitation in the catchment basin. " The fluctuation of the rainfall is exactly reflected in the change of level in the Caspian Sea."
6 According to Woeikoff the Caspian Sea receives yearly on an average a volume of water which would raise its level by 43 inches—if it were not wasted by evaporation ; the sea, then, receives an afflux of 215 inches in five years. If, then, from the period 1861-65 to the period 1866-70
it there has been a rise of 15 inches, this value gives the excess of discharge into the sea over evaporation, an excess which corresponds to the increase of the precipitation.
Bruckner shows that since the beginning of the nineteenth century wet and cold periods have alternated
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