In recent years, it seems that sand storms are affecting Chinese
people's lives more frequently and extensively. As this spring
draws near, more sand storms are expected. Among the many Chinese
scholars probing the reasons and controlling measures of the sand
storms, Wang Shejiao, of the Northwest Historical Environment and
Economic Social Development Research Centre under the
Shaanxi
Normal University, has put forward a rather unique view.
In
his article "Research on the Distribution and Reasons of Dusty and
Sandy Weather in Chinese History," published in the 12th issue of
the Chinese magazine "Xinhua Wenzhai (digest)," Wang noted that
dusty and sandy weather is far from being a new disaster in China.
Historical records indicate there have been many serious sand
storms sweeping across the country. China Daily staff reporter Liu
Jun reports Wang's views.
In
the Eastern Han Dynasty (25-220), historian Ban Gu set aside the
"Wuxingzhi (Records of Five Elements)" in his work "Hanshu (History
of Han)" to record the disasters and strange phenomena occurring
from the Spring and Autumn Period (BC 770-BC 476) down to the end
of the Western Han Dynasty (BC 206-AD 24).
Following this tradition, most works of Chinese dynastic histories
called the "Twenty-Four Histories" have recorded natural disasters.
Traditionally, the "Twenty-Four Histories" have taken up the
authoritative position in the recording of Chinese history. Thus
Wang mainly based his research on these annals.
According to modern meteorology, dusty and sandy weather can be
roughly put into three ascending categories.
Floating dust happens with or without little wind. The dust is
either carried to the present location by high-altitude air
currents or is suspended evenly in the air after a sand storm. The
visibility when floating dust occurs is less than 10 kilometres.
The sun appears white and any distant scenery is yellow brown.
The next level is floating sand, which is blown into the air by
strong wind. The air is rather indistinct and visibility is between
1-10 kilometres.
The highest level is of course the sand storm. The powerful wind
takes ground sand and dust into the air, lowering visibility to
less than one kilometre. The sky appears dusty brown or even
reddish brown.
Wang found that in Chinese annals, there have been very specific
recordings of dusty and sandy weather.
For example, in the "Records of Five Elements," Ban Gu said that
the northwestern sky seemed to have caught fire one night. The next
morning, powerful winds came from the northwest. The wind appeared
reddish brown and quickly filled up every corner of the sky.
Throughout the day and night, yellow dust fell on the earth like
rain.
Among the recordings, Wang found several appalling notes about the
aftermath of the disasters.
In
the "Songshi (History of Song)," it is said that in the year 1007
under the reign of Emperor Zhenzong in the Northern Song Dynasty
(960-1127), a strong wind brought yellow dust that shrouded the
sky. The farm fields around the capital were destroyed.
The "Mingshi (History of Ming)" records that in 1590 during the
Ming Dynasty(1368-1644), a wind storm carrying sand and dust lasted
from morning till night. Numerous houses were devastated.
The most difficult thing in studying the historical records of
disastrous weather was finding out the precise location of the
disaster, Wang said. About half of the weather records in the
"Records of Five Elements" of the "Twenty-Four Histories" are vague
in the locations of the climatic disasters.
In
ancient China, everything abnormal in nature was seen as some sort
of hint from heaven. These phenomena had to be reported to the
Emperor and recorded by historians.
For the reports sent by local officials, a precise location was
usually indicated. But when historians directly noted disasters
that took place near the nation's capital, they normally omitted
the location.
Thus Wang treated all the records without a location as meaning a
place near the dynasty's capital. Through this, he was able to find
out the geological changes of the dusty and sandy weather in
Chinese history.
Cycle of sand storms
From the 4th century BC until 1900, Wang put the occurrence of
dusty and sandy weather in China into four periods.
"Observed on a time scale, the occurrence of such disastrous
weather is becoming more frequent, serious, longer and extensive,"
said Wang.
There were only two records about the dusty and sandy weather
before the 4th century BC. From the 4th till the 10th centuries, 39
such disasters happened. The figure grew to 97 between the 11th and
15th centuries, then 115 in the 400 years before 1900.
In
the spring of 1677 during the rule of Emperor Kangxi of the Qing
Dynasty (1644-1911), a sand storm lasted for over 40 days. Such a
record is rather rare, Wang noted.
While the general trend of dusty weather is increasing, Wang
pointed out that there have been five peak sand storms between
valley periods.
It
is worth noticing that before 1051, there had only been five cases
of dusty weather within a time span of 50 years. But from 1051 till
1100 within the Northern Song Dynasty, the number sharply rose to
13. From 1151 till 1200 during the Southern Song Dynasty, an
astounding number of 27 sand storms took place, more than that in
any 50-year spans between the 4th century BC and 1900.
In
contrast, from 1368 till 1463 during the Ming Dynasty, Wang didn't
find any records of dusty and sandy weather.
As
for the seasons in which dusty and sandy storms took place the most
frequently, spring took up 71 per cent among all the 252 records
with clear seasonal indications. Winter took up only 7 per cent,
while summer and autumn together took up 15 per cent.
Apart from time, space is another element Wang has focused his
studies on.
While dusty and sandy weather visited the vast region to the north
of the Yangtze River drainage area, the Yellow River and Haihe
River drainage areas had been the main stage for such destructive
forces of nature.
As
the sandy wind blew stronger, it also affected more places in
China. Before the 10th century, the middle and upper reaches of the
Yellow River often witnessed sand storms.
Between the 11th and 14th centuries, the location of sandy weather
gradually moved eastward. The area to the east of today's Xi'an
(the capital of Northwest China's Shaanxi Province), west of
Shijiazhuang (the capital of North China's Hebei Province), north
of Zhengzhou (the capital of Central China's Henan Province) and
south of Hohhot (the capital of North China's Inner Mongolia
Autonomous Region) was frequented by the most sandy
catastrophes.
From the 15th till the 19th centuries, sand storms moved further
east to today's Hebei, Henan and Shandong provinces and the large
cities of Beijing and Tianjin.
Formation reasons
Modern studies have found that dusty and sandy weather results from
four necessary conditions: powerful and lasting wind, dry climate,
loose earth and sparse vegetation.
Chinese meteorologists have drawn an outline of the wind features
in China. The country's northeast, north and northwest including
the Qinghai-Tibet Plateau have 10 to 75 days of powerful wind,
which blows at an average speed of 2 to 4 metres per second.
In
China's southwest, south and the Yangtze River drainage area, the
wind is rather moderate, at 1 to 3 metres per second. In this area,
only five to 25 days have strong wind annually.
Spring and winter are the two seasons when the wind is at its
strongest in China. In some areas of North China, the wind can
reach 6 metres per second.
Contemporary meteorological studies coincide nicely with the
climate records of Chinese history, Wang said. Among the 254 sand
storms recorded in annals, 115, or 45 per cent took place
accompanied by strong wind.
The places where windy and sandy days occurred most frequently are
usually places with dry climate zones, with sparse vegetation
growing on sandy earth. The Loess Plateau at the middle and upper
reaches of the Yellow River, for instance, is piled high with very
loose yellow dust, which is prone to flying into the air even if
the wind is not very vigorous.
Zhang also noted that the appearance of sand storms has certain
connections with human activities.
In
the Qin (BC 221-BC 206) and Western Han dynasties, the rulers moved
people to the northwest and cultivated farm fields. This first
round of land exploitation in Chinese history brought the first
record of dusty days during the reign of Emperor Chengdi (BC 32-BC
7) of the Western Han Dynasty.
In
the Eastern Han and following dynasties, the governments could not
spare much time from the wars to continue cultivating the
northwest. Farmers moved out of the Loess Plateau and the
vegetation quickly recovered. It wasn't until 280 years later that
the second record of dusty days appeared in the early years of the
Eastern Jin Dynasty (317-420).
Before the Ming Dynasty began in the 14th century, the nation's
agricultural development mainly concentrated in the upper and
middle reaches of the Yellow River, a region where the sandy
weather frequented in this period.
The Ming Dynasty saw the unprecedented expansion of cultivation.
The vast areas surrounding Beijing, Hebei and Shandong were
gradually shrouded in more dusty storms.
However, Wang noted that the undulation of dusty and sandy weather
occurrences doesn't necessarily synchronize with the changes of
human activities.
From the end of the Eastern Han Dynasty till the early Sui Dynasty
(581-618), China was trapped in consistent and numerous wars. The
farming population sharply decreased. On the Loess Plateau, nomadic
tribes from North China turned the old farm fields into
pastures.
Instead of declining or remaining on a low level, the dusty and
sandy days of this period rose much higher than previous periods.
In the half century between AD 501 and AD 550 during the Southern
and Northern Dynasties (420-581), six sandy storms took place, the
highest record only to be surpassed until 500 years later, when 13
sand storms occurred between 1051 and 1100.
When the Ming Dynasty reached its prime from 1368 till 1463, the
population quickly multiplied, with farm fields expanding at an
unprecedented rate. But no sandy storms occurred for nearly a
century.
"Human activity has certain influences on the occurrence of dusty
and sandy weather," Wang said. "But the determining factor is still
with nature itself."
"To prevent or lower the level of dusty and sandy weather, we
should protect and restore the vegetation in areas where such
natural disasters are prone to happen," Wang said.
(
China Daily
January 28, 2002)