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Friday, 28th May 2010

Sandstorms (2)

There is no lack of accounts of sandstorm in history. Here is a wonderful description by T.E. Lawrence (1888 - 1935, widely known as 'Lawrence of Arabia') :

"When it got near, the wind, which had been scorching our faces with its hot breathlessness, changed suddenly; and, after waiting a moment, blew bitter cold and damp upon our backs. It also increased greatly in violence, and at the same time the sun disappeared, blotted out by thick rags of yellow air over our heads... "

"... these internal whirling winds tore our tightly-held cloaks from our hands, filled our eyes, and robbed us of all sense of direction ...... while large bushes, tufts of grass, and even a small tree were torn up by the roots in dense waves of soil about them, and driven against us, or blown over our heads with dangerous force. We never were blinded - it was always possible to see for seven or eight feet to each side - but it was risky to look out, as, in addition to the certain sand-blast, we never knew if we should not meet a flying tree, a rush of pebbles, or a spout of grass-laden dust. This storm lasted for eighteen minutes, ... "

Figure 1.   T.E. Lawrence, 1917
Figure 1.      T.E. Lawrence, 1917


Here is an equally powerful account by Hassanein Bey (1889 - 1946, 'bey' is a Turkish term for 'lord') :

"It is as though the surface were underlaid with steam-pipes, with thousands of orifices through which tiny jets of steam are puffing out. The sand leaps in little spurts and whirls. Inch by inch the disturbance rises as the wind increases its force. It seems as though the whole surface of the desert were rising in obedience to some upthrusting force underneath. Large pebbles strike against the skins, the knees, the thighs. The sand-grains climb the body till it strikes the face and goes over the head. The sky is shut out, all but the nearest objects fade from view, the universe is filled."

Historical accounts of sandstorms by Chinese were generally brief, but no less violent in terms of their destruction :

"There was high wind in Wuwei (Gansu) in February, with dust descending from a yellow fog. Trees were uprooted, houses torn down, and many people and animals killed." (351 CE)

In his journey to India, Fa Xian (337 - 422 CE), a well-known Chinese Buddhist monk, wrote: "There was a ghostly hot wind in Sha He (Xinjiang), killing everybody it touched and ripping them to pieces."

Following his footstep two hundred years later, Xuanzang (602 - 664 CE), the best known monk in the Tang period, reported: "The stormy wind developed suddenly, blew sand and rained down stones, killing everybody that encountered it and smashing them to pieces."

Conditions required for the formation of sandstorms are, in general : -

a)   a source(s) of sand;
b)   unstable atmosphere, to take the sand to great heights (e.g. intense solar heating);
c)   high wind, to give the storm momentum.

In China, sandstorm reports have generally been on the increase after the 13th century during the period 3rd century BC - 20th century. This is believed to be a result of population expansion as well as movement of people to the frontiers from time to time, which inevitably led to increased cultivation, grazing and deforestation. Irrigation of newly cultivated land practically meant that water supplies were reduced further down the river or waterway, resulting in degradation of farmland downstream. This started the gradual process of retreat of farmland as a whole to the east and south. The situation was aggravated by warfare and climate change, both leading to land desertion. Deserted land, once barren, would not easily revert to natural grassland because of the effect of wind erosion. As a result, desertification intensified. Incessant invasion of horsemen from the north in earlier years did not help, in fact exacerbating the vicious circle of vegetation retreating further towards the east and south.

Climate change in the 20th century works further havoc. Beijing's annual rainfall in the 1990s had fallen to 600 mm from nearly 800 mm in the 1950s, while temperature has been on the increase. The combined effect of decreasing rainfall and increasing temperature means that without irrigation, the moisture in soil would be gradually lost, and this weakens its resistance to wind erosion. It was not until the mid-20th century that large-scale reforestation and land management began.

It appears that people still have to confront the various challenges until the situation improves.


References

(1)   'Sandstorms', Meteorological Publishing Co., 2003 (in Chinese only)
(2)   'Meteorological history of China', Meteorological Publishing Co., 2004 (in Chinese only)
(3)   Wikipedia


B.Y. Lee



Last revision date: <17 Jan 2013>