PART III TELECONNECTION :
3.1 THE EXISTENCE AND
THE STRENGTH OF EL NIÑO TELECONNECTIONS
Climate
in China is mainly controlled by the Asian monsoon. Because extreme
climate events such as drought and flood have tremendous negative impacts on
society and economy in China, Chinese scientists
have spent great effort to search for possible links between anomalous signals
in the global climate system and climate variations in China. The El Niño cycle has become the latest target in both the
academic research and
the operational forecasting communities. Their preliminary
results showed that, although in tropical regions especially in the tropical
Pacific, El Niño has the most significant impacts on
climate, its impacts on climate weaken beyond the tropical regions and away
from the Pacific. In China, most forecasters
believe that El Niño is only a strong signal that
could be used for constructing predictions of climate anomaly in China. There are still
mechanisms that are not yet fully understood about the relationship between El Niño and various climate hazards in China. It is very difficult
to identify kinds of specific anomalies that could occur in which part of China during El Niño years (Zhao, 1997).
Chinese
forecasters noticed for many years that summer monsoon rainfall in China depended significantly
on the intensity and location of the subtropical high over the northwestern Pacific Ocean at 500 hPa; this links sea surface temperature anomalies (SSTA)
over both the warm pool in the western Pacific Ocean and the El Niño regions in the central and eastern Pacific. Based on
statistical analyses of historical records, certain correlations between El Niño and climate anomalies in China are the following:
l
In El Niño years, with rising SSTs in
the eastern equatorial Pacific and decreasing SSTs in the equatorial West
Pacific, the East Asia monsoon is weaker, and the subtropical high in
the Western Pacific Ocean moves southward. As a result, the main
monsoon rain band in China during the summer rainy
season shifts toward the south and stays to the south of the Yellow River Basin. An increase in
precipitation in the Yangtze-Huaihe River Basin can be expected. In the
north of China, especially in the Northern China area and in the Yellow River Basin, there is reduced
precipitation (Huang, 1990; Liao and Zhao, 1992;
Zhao, 1996; Liu and Ding, 1992; Chen, 1995).
l
In the autumn and winter of El Niño
years, it will be drier in most parts of north China and wetter in most
parts of south China (Figure 4).
Figure 4: The distribution of abnormal
precipitation in autumn of El Nino years.
The Tibetan
Plateau receives above average snow. The Meiyu normally occurring in May will be delayed in the middle and lower
reaches of the Yangtze River.
l
In El Niño years, Chinese winters are
warmer and summers are cooler. For example, warm winters appeared in 90 percent
of El Niño years since 1951 (Figure 5).
Figure 5: Deviations of the temperature grades in winter
(white columns represents normal years, black columns represent La Nina years
and lined columns represents El Nino years; the values above the zero line
represent high temperature, and the values below are the opposite).
In addition, since 1951, several cold summer years
in Northeast were related to El Niño years. This
relationship has changed since 1980s when the global climate became warmer.
Although the occurrence of El Niño events increased
since the mid 1970s, the appearance of cool summers decreased in the Northeastern China. During the El Niños in the 1990s, there were no cool summers in China.
l
In El Niño years the number of typhoons,
which form in the northwestern Pacific Ocean and the South China Sea, is
reduced as well as the number of typhoon landings in China. The relationship between typhoons and El Niño events is more direct than the two relations noted
above. The correlation coefficient between the number of typhoons in the
northwestern Pacific and the number of landings in China and SSTA in the global
ocean show that few typhoons occur during the ENSO events (Zhao Zongci, personal communication). An above average number of
typhoons occurs in La Niña years. However, currently
there are no studies on the strength, landing time and location in China of typhoons related
with El Niño events. The damages caused by typhoons
in both El Niño and La Niña
years have not been studied yet because of the lack of reliable and useable
data.
Although some climate anomalies in China do have statistically
significant relationships with El Niño, the
mechanisms behind those relationships are still not clearly understood.
Particularly in the context of global warming, scientific uncertainty
surrounding these mechanisms is increasing. For example, during the El Niño events in 1969, 1972 and 1976, temperatures in summer
were well below normal in Northeast China, which contributed a
great loss in crop production. Summer temperatures were only slightly below
normal in the 1982-83 and 1986-87 events and their impacts were weak. During
the period of the prolonged El Niño event from 1990
to 1995 and the strong one of 1997-98, low summer
temperatures did not occur. This has happened before; the 1896, 1899-1900,
1925-1926, 1963 and 1965 El Niño events did not lead to low summer temperature in the Northeastern China.
The relationship between El Niño
and Chinese summer precipitation is complex and unstable. For example,
1931,1954 and 1991 are the three strongest Meiyu years in the 20th
century. In these years, big floods occurred
in the Yangtze River Basin, and caused huge
damages to human life and property. These years, however, are not El Niño years. The 1982-83
El Niño event was one of the strongest events in the
20th century besides the
1997-98 El Niño event. But in 1982 and in 1983, there were no major
climate disasters in China. At the end of the
1997-98 El Niño event, there was the great flood in
the summer of 1998.
In summary, although El Niño
can lead to extreme climate events such as floods and droughts somewhere in China, more scientific work
is needed to confirm the proposed teleconnections. At
the current time, there are too many uncertainties to reach any solid
conclusion about El Niño impacts on China’s climate.
3.2 climate anomaliEs related to the 1982-83 El Niño
In
1982 and 1983, there were no significant climate-related hazards in China. No severe floods and
droughts occurred and the number of tropical storms was normal. One exception
was in the Northeastern China where low temperature and cold problems
appeared in summer.
3.3 What were
the climate-related physical and social impacts of the 1997-98 El Niño in China?
What is the reliability of those attributions?
3.3.1 The physical impacts
During 1997 and 1998, anomalous climate in China included an unremitting
heat wave and dryness in North China, dramatic
heavy snowstorms on the Tibetan Plateau, and the Great Flood of the Yangtze River. The number of typhoons formed in the Western Pacific Ocean and making landfall in China was less than normal. All of these
anomalous climate phenomena were considered to have been related to the 1997-98 El Niño
event.
Since
March 1997, the SSTs in the equatorial East Pacific had become increasingly high.
Based on historical records, this
anomalous condition in the Pacific
could have led to anomalous
climate conditions
in China as suggested in Table 3, which lists an index
for the standard SST departure for
March-August in the Niño-3 region from 1951
to 1998. In the 14 strongest years (i.e., when the index summation
was greater than 200), the summer atmospheric circulation and the climate of China showed significant anomalies. According to the
previous studies, when the ENSO event begins in spring and summer, the tropical
atmospheric circulation changes rapidly. The Walker
Circulation is weaker and shifts eastward. The position of the subtropical high over the western
Pacific shifts southward. As a result, in the middle of China the rainfall was stronger in summer
and the temperature was lower. The number of typhoonsmaking landing in China decreased too.
Table 3. The atmospheric
circulation in summer and the main anomalous climate of China in the years when SSTs
increase anomalously during spring and summer
|
Year
|
|
Major Climate Anomalies
|
|
Flood or Drought
|
Anomalous Temperature
|
No. of
Typhoon Landfall
|
|
1983
|
884
|
Floods in mid and low reaches of the Yangtze
River
|
Frost damages in Northeast China
|
5
|
|
1997
|
781
|
Droughts in South China
|
Heat waves in South China
|
4
|
|
1987
|
708
|
Floods in mid and low reach of the
Yangtze River
|
Low temperature in Northeast China
|
5
|
|
1992
|
624
|
Droughts in most parts of China
|
|
8
|
|
1957
|
558
|
|
Frozen damages in Northeast China
|
5
|
|
1993
|
541
|
|
Cool summer
|
7
|
|
1969
|
469
|
Floods in mid and low reaches of the Yangtze
River
|
Frozen damages in Northeast China
|
5
|
|
1972
|
462
|
Droughts in South China
|
Frozen damages in Northeast China (
|
6
|
|
1965
|
417
|
Huaihe River Flood
Droughts in South China
|
|
8
|
|
1991
|
283
|
Yangtze-Huaihe River Basin Flood
Drought in North China and to
south of the Yangtze
River
|
|
6
|
|
1963
|
251
|
Great floods in the North China
Severe droughts to the south of the Yangtze
River and in the middle reaches of the Yellow River
|
|
7
|
|
1953
|
235
|
|
|
7
|
|
1994
|
223
|
Great floods in the South China
|
Frozen damages in the South of China
|
12
|
|
1976
|
211
|
|
Frozen damages in Northeast China
|
6
|
|
|
|
|
|
|
Table 3 shows that the impacts of ENSO on the circulation at
the middle and high latitudes and on the climate of China as a result of teleconnection are very complicated when it comes to attribution. The climate anomalies of China could be caused by many
other factors. The rate of development and the intensity of an ENSO extreme
event, however, was a very important consideration, when Chinese scientists made their
predictions on climate anomalies in China during recent years
(Cheng, 1998). For
example, by
including the ENSO signal in various forecasting models, the National Climate Center was able to claim a
successful forecast for the anomalous summer precipitation in 1998.
The
1997-98 El Niño began in May 1997, and reached its peak in November and
December (Figure 6).
Although the strength of this strong El Niño declined in the first half of 1998 and the SSTs in tropical Pacific Ocean were back to normal in June 1998, this El Niño had a
great impact on summer precipitation in China. It was one of the key
factors causing the great amount of precipitation in the Yangtze River Basin in the summer of 1998. Figure 7
Figure
7: Monthly variations of global SST anomalies from January 1998 to October 1998
shows
the monthly variation of the global SST departures from January to October 1998. The SSTs in the equatorial Pacific had a positive departure from January to April,
began to descend in May, changed into a negative departure from average after
June, and gradually entered the La Niña mode. In the Western Pacific, the most distinct
feature was that the SST
anomalies were positive in the South China Sea and the inshore sea
area of the east of China from January to April.
When the SST anomalies in the Indian Ocean turned negative, the sea around the southern China still had distinctly warmer SSTs. The
east part of China was encompassed by warm
seawater which had appeared since September 1997. The heating from the inshore sea in summer reduced the
thermodynamic difference between sea and land and, in turn, the Asian summer
monsoon weakened. As a result, the main
rainfall band in summer was very stable in the Yangtze River Basin. These circulation
anomalies are the main reason for the climate anomalies of China, and they are
influenced by 1997-98 ENSO event and other factors.
In addition to ENSO’s impacts, there were some other important factors that
played an important role in the climate anomalies of China.
1.
Heavy precipitation in the Qinghai-Tibet Plateau in winter and spring
From
December 1997 to February 1998, the amount of snowfall was excessive in most parts of the Qinghai-Tibet Plateau. There were record-setting snowstorms
in many places. The anomalous
atmospheric circulation continued until April 1998 (Figure 7) with strong meridional circulation and
a stable blocking high. The ridge of the subtropical high over the Western Pacific was strong but located more southward than normal and, as a result, the location of the main summer rain band in China was southward.
2. The anomalous Asia monsoon
Figure 8
.
shows
the monthly departure of the strength for the South China Sea monsoon and the South Asia monsoon. Figure 8 shows that the South China Sea monsoon had negative departure (weak) from January to August. The South China Sea monsoon in April, May,
July and August is the weakest since 1980. The South Asia monsoon had negative
departure too, except in June and July. This indicates that both the South Asia monsoon and the South China Sea monsoon were weak in
1998, which led to the southern shift of the summer location of the subtropical
high in the Western Pacific. Hence, the major rain band located in the Yangtze River Basin and the south area of
the Yangtze River Basin.
3. The blocking highs in the mid- and high
latitudes
The
500hPa blocking highs in the mid- and high
latitudes, especially in East Asia, are the main circulation systems influencing the temporal and spatial distribution of precipitation in China. Previous studies indicate that Okhotsk, Baikal and Ural are
the three places where the blocking highs often form. When there are the blocking highs in East Asia in summer, the west
wind in middle latitude divides into two branches. Meanwhile, the frontal zone shifts to the south and the
location of the subtropical high in the Western Pacific Ocean moves to south. Usually, when the blocking highs become established in Okhotsk or Baikal in summer,
the Yangtze River Basin receives more than
normal precipitation in summer.
Figure 8 is the variation of the mean circulation index
in 500 hPa in Asia from January to
December 1998. The meridional
(West-East) circulation developed from June to August and the latitude
(South-North) circulation developed from September to December. The anomalous
circulation caused higher than normal temperatures in most areas of China in spring, autumn and
winter. Moreover, the development of
anomalous circulation in summer led to excessive rainfall in the Yangtze River Basin, the Nengjiang River Basin and the Songhuajiang River Basin.
4. The anomalous movement of the subtropical high over the West Pacific Ocean
Figure 9
Figure
9: Climate-mean position and the daily variations of positions of the ridge of
the subtropical high in the West Pacific. (The thick line represents the
subtropical ridge in 110--1300E, and the thin line represents the
average subtropical ridge from 1976 to 1996).
is the comparison between climate mean and
daily movements of positions of the subtropical high in the West Pacific. Clearly, the subtropical high
jumped to the south from the mid-June to the end of June. During these twenty days, continuous rainfalls
occurred in the Yangtze River Basin, especially in the
north and upper streams of the Yangtze River Basin with very strong precipitation. From mid-July to early August, the subtropical high
inclined to the south for an anomalously long
period. It even receded to 15N at one
time, which is rare in history. Then, the second phase of anomalous summer rainfall in the Yangtze River Basin began. Figure 9 indicates that the
location of the subtropical high remained to the south during the whole summer
except for the third 10-day period of June to the second 10-day period of July.
So the last anomalous shift to the south of the subtropical high is another
important reason for the anomalous abundance of summer precipitation in the Yangtze River Basin at that time.
5. The weak equatorial convergence zone
In
the summer of 1998, the equatorial convergence zone was unusually weak, and the
number of typhoons was well below average. Only 3 typhoons landed in China in 1998, a year with
the fewest typhoons in history. The first time a tropical storm landed in China in 1998 was on August 4, the latest time in history. It is the
direct result of the weak Asian monsoon and the deflection to the south of the
subtropical high in the West Pacific. Under these conditions, the eastward
deflection of air current prevailed over a large area of the tropical West Pacific Ocean and as a result, the
southwest monsoon was
unable to reach the tropical West Pacific. The equatorial convergence zone formed
by eastward deflection of air currents and the southwest flow was, thus, very
weak or did not exist at all. The anomalies in the equatorial convergence zone which is the main “birthplace” of
typhoons allowed very few
typhoons to form in the western Pacific Ocean.
Based on the above
discussion, there is clear evidence that the El Niño event in
the 1997-98 winter and spring led to the anomalous atmospheric
circulation over China, which, in turn, caused many climate
anomalies around the country. Unfortunately, there are still many uncertainties
in the relationship between the ENSO and the occurrence of the atmospheric
circulation in
China. More scientific research is needed along with an
improved ocean observation network and improved atmosphere-ocean coupled
numerical models.
3.3.2 Impacts of the 1997-98 ENSO on society and the economy
In
1997 and 1998, many weather and climate anomalies occurred in China. They greatly affected daily life and economic development of society
and the economy. The floods around the country caused great loss in
both property and human lives. Meanwhile,
droughts also occurred and greatly damaged agriculture.
The following information relates to some impacts of weather and climate
anomalies during the 1997-98 El Niño.
1. Nation-wide
damage caused by excessive rainfall and flooding
In
the summer of 1998, a
major flood occurred in the Yangtze River Basin, which caused great damage to human
lives, property and the national economy.
Since the beginning of the winter
in 1997,
the subtropical high in the Western Pacific Ocean developed anomalously, and its intensity was the
strongest since 1949. Intense rainfall events occurred frequently in the south
of the Yangtze River Basin. The amount of precipitation was much more than the climatological average. In many places, the amounts
of precipitation broke historical records. In this region, some rivers and lakes exceeded the cautionary
water level reaching the highest water levels in regional history. Rare winter floods occurred.
From
mid-November in 1997 to early March in 1998, there were continuous rains
and snows in most parts of the Southern China. The total amount of precipitation ranged
from 300 to
600 mm in most places. South of the Huaihe River was 1.5 times more than climatological mean. Recorded precipitation at most weather stations in this region was the largest rainfall for the same period
during the past 40 years (Figure 10,
Figure 11, and Figure 12).
Continuous rainfall led to the rising water level for some rivers and surpassed critical levels. Wintertime flooding occurred in some rivers. For example, the Xiangjiang and Ganjiang Rivers in Hunan Province, the Mingjiang River in Fujian Province, the Beijiang River each had flooded. On 16 March,1998, the water level at Hankou (a
city in the middle reach of
the Yangtze River) reached 21.33 meters, which was the highest value ever recorded at this station. Spring flooding in Jiangxi and Hunan provinces had occurred one month earlier.
In
early November 1997, it was warm in Zhejiang Province located on the east
coast. Based on the records of eleven weather stations in Zhejiang, there was no rain in
the whole province for a 70 days period before mid-November. After that there
were endless overcast and rainy days until the end of the year. Continuous
rainfall occurred from November 12 with total amount of 1.5 to 3.5 times more
than usual in all locations. The rainfall in Quzhou, Longquan, Jinhua, Ningbo, Chenzhou
and Zhoushan set their maximum values for the past 40
years. For example, the rainfall in Quzhou for
November was 290mm, which had never been seen in the instrumentrecorded
history of Zhejiang in winter.
In
the last twenty days of November 1997, south China was under the influence
of the warm moist air from the southwest, resulting a rainy weather in some
areas. Rainfall amount increased significantly. Starting on November 24, in
northern Jiangxi Province and in the middle of Zhejiang Province, two rainstorm events
occurred. The weekly rainfall totally reached 100-200m which greatly exceeded
the maximum on record.
The
rainfall for November 1997, in Jiangxi Province exceeded the maximum
amount in history. The rainfalls in most areas were three times as much as the climatological averages. On November 25, hail and
rainstorms affected Zixi, Nancheng
and Ruijin counties. On November 28, the water levels
of some segments of the Xingjiang River in Northeastern Jiangxi Province exceeded a critical
level. It was rarein the history of Jiangxi Province. Rain continued to fall
in the southern part of the Yangtze River Basin in December. The
precipitation for the entire winter in many places of Jiangsu Province was far greater than
that in a normal year (Figure 13).
In
mid-January 1998, heavy snow fell in most areas of Northern China with severe rainfall in
the Southern China as shown in Figure 14.
In the spring of 1998, several strong cold
waves hit China, and the crops were
severe damaged by frost. Meanwhile, in most parts of South China, the rainfall lasted 20
days or so and led to flooding. The anomalous climate badly affected the growth
of crops. The respiration of crops became difficult once the fields were
covered in water for a long time. Moreover, crop diseases were aggravated. All
these calamities adversely affected agricultural production.
In
Jiangsu Province, agricultural output
was reduced by about 28%. The total production of crops was 3.6 million tons
less than the previous year, and the reduction was almost 30%. The percentage
of crop reduction in 1997 was not only the largest year in recent history but
also the second lowest-production year since 1980. This extremely wet winter
also increased soil moisture to a very high level and delayed many flood
control projects. The stage was set for summer floods.
During
the main rainy season (June-August in China), the main centers of
precipitation were in the Yangtze River Basin, west of Northeast China and the east of Inner Mongolia (Figure 15).
Figure 15: The distribution of precipitation departure (%) from June to
August in 1998
Precipitation
in most regions was well over the normal amount (Figure 16)
Figure 16: Trend (solid line) of the annual precipitation
(mm) from June to August. The average is based on 336 stations in China from
1950 to 1998. The dashed line is the average value for the same period.
with
continuous strong rainfall events in some places. For example, there were about
700-900 mm of rainfall north of the Yangtze River Basin, southwest of Hubei Province, in the City of Chongqing and to the east and
southwest of Sichuan Province (Figure 17).
Figure
17: The distribution of precipitation from June to August in 1998. (mm)
Then,
the great flood occurred in the whole Yangtze River Basin ranking second since
1950. Meanwhile, a record-setting great flood occurred in the Nenjiang and Songhuajiang Basins in the northeast of China. Moreover, the Xijiang River in the Zhujiang River Basin and the Mingjiang River Basin had unusual floods,
too. It is rare in Chinese history that so many rivers and lakes had
record-setting floods at the same time and lasted for a long period of time.
At
the beginning of the summer of 1998, the subtropical high in the Northwestern
Pacific was the strongest one on record. The convection band stayed stalled
over the middle and lower reaches of the Yangtze River Basin starting in mid-June.
Rainstorms and very heavy rainstorms hit this area continuously. Then, after
moving northward for a short period of time, the subtropical high moved back to
the Yangtze River Basin in mid-July bringing
with it continuous, strong precipitation processes for a second time. The water
from Dongtin Lake, Poyang Lake and many small rivers
constantly flowed into Yangtze River. The water levels in
the middle and lower reaches rose suddenly and at the same time. As a result,
the great flood occurred in whole basin.
The
whole process of the 1998 Great Flood in the Yangtze River Basin can be divided three
periods:
(1)
The first period was from mid-June to the end of June. At the beginning
of June, the Meiyu season started in the Dongtin Lake and the Poyang Lake. In mid-June,
continuous rainstorms occurred in Jiangxi, Hunan, Zhejiang, Guangxi
and Fujiang provinces. In these provinces, the total
precipitation from June 12 to June 27 ranged from 200 to 500 mm. To north of Jiangxi, north of Hunan, southwest of Zhejiang,
south of Anhui, northwest of Fujian
and northeast of Guangxi, the precipitation reached
600—900 mm, and some locations exceeded 1000mm. It was rare in the country’s
history that so much precipitation fell in so short time. The rainfall amount
was about 2 times more than the average. Most places achieved a new maximum for
their historical records (Figure 18,
Figure 19).
As
early as in February, winter floods occurred in the Xingjiang River and the Fuhe Rivers, which made the water
levels of rivers and lakes in the middle and lower reaches of the Yangtze River Basin dangerously high, later
reaching their highest levels in history in summer (Figure 20).
After
June 28, the subtropical high moved to the west and shifted to the north. The
rainfall in the middle and lower reaches of the Yangtze River Basin decreased, and the
flooding of the Yangtze declined.
(2) The second period was in late July. From
July 20 to 31, because the strength of the subtropical high had been reduced,
it retreated to south and to the east. Large scale rainstorm processes occurred
in the middle and lower reaches of the Yangtze River Basin. Compared to the first
period, the rainy area was smaller and the rainy period was shorter. The
rainfall, however, was heavier and formed downpours. As a result, the water
level rose very rapidly.
In
this period, precipitation in most areas of the Yangtze River Basin reached 90
to 300mm. Northwest of Hunan, north of Jiangxi, and
south of Hubei, precipitation amount reached
300--500mm, and in some locations exceeded 800mm with a maximum of 911mm (Figure 21, Figure 22, and Figure 23).
In the previous period, the water level in the
Yangtze was already very high, and exceeded the damage level. So, continuous
precipitation in this period was really disastrous.
(3) The third period started from the beginning
of August. Although the precipitation in the middle and lower reaches of the Yangtze River decreased greatly in
August, precipitation increased continuously in the upper reaches of the Yangtze River in Sichuan Province, Chongqing, the Three Gorges area,
the Qingjiang River Basin and in the Hanjiang River Basin. The total amount of
monthly precipitation ranged from 150 to 250mm, and in some areas exceeded
300mm.
Frequent
precipitation in the upper reaches led to the repeated occurrence of flood
peaks. There were five peaks in August. On August 7, the dike in the Jiujiang segment was broken and torrential water swarmed
into cities, villages and agricultural fields. There was severe damage to
property and loss of life.
The
Yangtze flood did not subside until late August. The total time of the floods
was about three months. It was the one of the most disastrous floods in
this century, and had
severe impacts on society.
In
1998, the rainy season in the Nenjiang River Basin in Northeastern China came early. As early as late May, rainy days
increased significantly. From June to September, the total precipitation in
most areas of this basin reached 300-450mm and in some places it reached
500-700mm. From June 5 to June 25,
there was rain almost every day. With such frequent rainfall, the water level
in the branches of the Nenjiang River rose continuously.
Flooding occurred frequently. There was a total of four flood peaks during
the season. On August 11, the greatest flood in the
recorded history of the Nenjiang River Basin occurred. In the Songhuajiang River Basin located along the border between China and Russia, the water level of Haerbin City (the capital of Heilongjiang Province) reached 120m on August 23, which was almost
0.84m higher than the historical record. The rate of water flow
reached 17,000 m3/s.
The
damages caused by the 1998 Great Floods were severe in the Yangtze River Basin, SonghuaJiang River Basin and other major rivers around China. Based on statistics, twenty-two provinces suffered flood disasters to different degrees. The provinces that suffered the most were Jiangxi, Hunan, Hubei, Heilongjiang, Inner Mogolia and Jining. Nation-wide, crops on about 310 million mu (1 mu=666.6 square meter) of farmlands were destroyed. More than
223 million people suffered from the flood
disasters. Officially, there
are 3,004 people dead and more than 5 million housed were collapsed. The direct loss was more than 166.67 billion yuan (RMB) (equivalent to $20
billion US dollar).
Although the 1998 Great Floods were no doubt attributed to the anomalous climate and excessive precipitation,
factors related to human activity
can not be overlooked. For example, large-scale deforestation since late 1950s
in the upper reaches in many river basins caused severe ecosystem deterioration. For quite a long period in history, the forest cover in the
Yangtze River Basin was estimated to be as
high as 60%~85% By 1957 it has been reduced to 22% and to 10% in 1986. Now it
is only about one percent.
This sharp decline on forest cover can be attributed to policy making for
economic development. In the 1950s, during the famous “Great Leap Forward Campaign”, people encouraged by the government rushed to
the plains, the foothills and the forests to find iron ore and fuels to make iron and steel. The forest resources in
these areas with dense populations such as the plains, foothill and valleys
were thoroughly depleted. Then,
to meet this unrealistic and unreachable economic development goal, people began to explore virgin forests in the areas such as the upper reaches of the
Yangtze and Yellow Rivers, west Sichuan Province and northwest Yunnan Province. The miserable degraded fate of forests in China began from then on, as
the amount of forest cover descended sharply. For example, in the middle part
of Sichuan Province, the forest cover for
53 counties, where branch basins of the Yangtze River are located, dropped to 3%, and it was1% in another 19 counties. In the mid-1960s, to prepare for possible wars with the Soviet Union and the USA, many of the factories in defense and high tech industries were
moved to
the inland areas. Most of these factories were established in remote mountains in order to avoid detection and a
nuclear attack. To supply these millions of workers and their families with enough food and other basic living needs such as housing, millions of trees were
cut down. In the late 1980s, in light
of the possibility for a more peaceful future for the world, these factories
were moved out. What they left behind was a series of unprecedented catastrophes such as
forest destruction, damaged ecosystem and polluted land.
Due to deforestation over the past 40 years,
a huge amount of nutrient
rich soils
flowed into rivers and lakes. The reservoirs and the rivers were silted up, and
the lakes shrank. People who lived
in the
upper reaches of the Yangtze River noted that, “In early days, the water in the river
was always lucid throughout whole year. But now, any rainstorms can lead to
floods, erosion and landslides. The Yangtze River became another Yellow River.”
The
rapidly increasing population is another factor that made the flooding severe.
The middle and lower reaches of the Yangtze River Basin are regions with
hundreds of lakes. The abundant lakes are a natural system adjusting for floods
in the Yangtze River Basin. With increasing
population, many lakes were drained and converted to farmland and residential
areas. In the 1950s, the total number of lakes in Hanjiang River Basin was 1046. Now, only 182
exist. Since the 1950, the water surface areas in Dongtinghu Lake was reduced by 46% and the Poyang Lake by 40%. As shown by the
National Statistical Bureau in recent years, the total loss of lakes in the
middle and lower reaches of the Yangtze River Basin has been as much as
12,000,000 hectares; the loss is as high as 34%. For example, Hubei Province used to be referred as
"The Province with One Thousand Lakes" in the Ming and Qing Dynasties. In the early 1950s, the total number of the
lakes, which have a water area greater than 100 mu,
was 1332. All these lakes had a capacity to hold floodwater of 11.54 billion m3.
By the 1980s, the number of the lakes with water area greater than 100 mu had been reduced to about 800. The effective adjustment
and storing volumes dropped to 3.7 billion m3, or about 26.6% of the
amount in 1950s.
As
a result, the capability of lakes to store floodwater and to reduce the flood
peaks became increasingly less. In addition, in the middle and lower areas of
the Yangtze River Basin, many factories were
constructed along watercourse, and a great amount of industrial garbage such as
gangue and scoria were emitted to the watercourses. All of these human factors
significantly reduce the capability of flood control.
A
third factor is due to the shortsighted view of economic development. Many
recent economic development plans focused only on the short term and on local
economic benefits. They paid little attention to the possible impact on the
environment. Many of the needed disaster-prevention and disaster-reduction
measures were impossible to put into practice. In some cities, there are no
prevention plans for natural disasters. In general, the country is lacking
usable knowledge about sustainable development, environmental protection and
reliable disaster-prevention and disaster-reduction plans. Construction of
disaster-prevention and disaster-reduction projects has lagged behind the rapid
development of the economy. The construction standard for flood-prevention
projects was low.
2.
Long lasting droughts and heat waves
In
1997, a prolonged drought occurred in southern China in summer and fall.
Such an event has been rarely seen in history in terms of its persistent,
wide-ranging impact and its degree of dryness. Meanwhile, precipitation was
reduced throughout the whole country, especially in most parts of Northwestern
and North China, and in some areas in the north of the Yellow River and the Huaihe River Basins.
In
the summer of 1997, temperatures in most areas of northern China were anomalously high
for a long period of time. The monthly mean temperatures in some northern provinces exceeded the highest in
recorded history. Endless heat waves and hot weather hit northern China continuously.
In
May 1997, the monthly mean temperatures were 20C - 40C
higher than the climate mean in the middle and lower reaches of the Yangtze River Basin and most areas of
northwestern China. In the first 10 days
of May, the maximum temperatures in the middle and north part of Jiangsu and Anhui provinces reached 350C
to 370C. These were the highest temperatures for this period since
1949. The hot weather appeared in the Yangtze River and the Huaihe River Basins half a month earlier
than normal.
In
early June and in July, heat waves hit Northeastern China. From June 13 to June
15, the maximum temperatures of Tailai in Heilongjiang Province in northern China, were 390C,
39.80C, and 37.70C respectively.
The
long lasting excessive hot temperatures were the main weather features of Liaoning Province (in Northeastern China) in July 1997. There
were almost 15 days when the daily temperatures exceeded 330C in the
whole province. In many places, the maximum temperatures set new records. With
little differences between day and night temperature, people felt extremely
uncomfortable all day long. With a headline
"Hot, Hot, Real Hot" in the Liaoning Daily, the hot weather totally affected the people's normal daily
life, although many retailers and manufactures did take advantage from it.
"Why
is the weather so hot?" became the headlines in many newspapers and on TV
programs, as well as having been a hot topic among people that summer. The
lasting high temperatures made Shengyang City (the capital of Liaoning Province) suffer under a hot sun
adversely affecting people in daytime. The hot weather with mean temperature
above 330C did not stop for half a month in July. Usually, this city
has the hot weather for 8 to 10 days with a mean temperature of about 280C,
and a maximum of 310C.
The
high temperature and the "Heat Island Effect" in cities made people
unable to stay in their homes at night. Department stores and cinemas equipped with
air conditions became places for people to escape to from the heat wave. The
sale of water heater, electric fans and air-conditioners increased
dramatically. Many shops had to add sales personnel. The assistant manager of
the appliance department of Shengyang Commerce City
Store noted that, "In that summer, air-conditioners, refrigerators,
water-heaters and washing machines, particularly air-conditioners, sold very
well. 400 air-conditioners were sold in 20 days in July, and more than 20
refrigerators were sold everyday. Air-conditioners are usually installed by
technicians sent by the factories. Because of many sales, it took 5 days to get
one installed. So, we had to hire outsiders to install air-conditioners for our
customers. We often worked till midnight during that time."
The manager of the appliance department of the Shengyang
Tiexi General Merchandise Stock Ltd. said, " The
hot summer in 1997 was not prepared for. We did not expect that the sale of
air-conditioners would go so well mainly because of the continuous hot weather.
According to statistics, sales increased about 3 times when compared to the
same period in 1996." Not only did the air conditioners become one of hot
items to buy, but beverages such as beer, soft drinks, and mineral water also
sold very well. For example, the price of famous brand pure water increased by
about 60% but was frequently out of stock. With a shortage of well-known brands
of beers in the market in Shengyang, many new names
appeared and had a good percentage increase in market share.
The
causes for the long lasting hot weather in Northeastern China, however, were quite
complicated. It is very hard to declare that the 1997-98 El Niño
was the only cause. For many El Niño years, according
to statistical results, Northeastern China often experienced cold
summers, which is the opposite to the situation in 1997. On the other hand, it
is also hard to rule out the influence of El Niño.
Since there have not been strong El Niño events such
as in 1997-98, it is not easy to reach any scientific conclusion on the
relationship between hot summers and El Niño.
In
August 1998, when the “super flood” was tyrannizing people in the Yangtze River Basin, record-breaking
high-temperature weather appeared in Shanghai. From August 8 to 15,
the maximum temperature of the seven days exceeded 380C. On August
11, the temperature reached 39.60C, and the record of the highest
temperature in Shanghai's history was
surpassed. According to the August 8-15 reports from in the XINMIN EVENING NEWS, daily life of Shanghai people was totally
disordered.
Afraid
of the scorching sun, few people were in the street. Most people stayed either
at home or in the office. General retail sales decreased by 20-30% in this
period. The heat wave put the owners of stalls and mobile dollies selling cold
drinks and ice creams on street out of business. In contrast, sales in the
air-conditioned indoor ice cream shops increased dramatically. Many people
enjoyed air-conditioning there for whole days. The prolonged hot weather also
made the taxi business change from an off-season to a booming season. To avoid
the burning sun, people increased their short-haul rides. Many people called to
order pickup and delivery services from their residences, which rarely occurred
before. According to the statistics shown by one taxi company (the Qiangshen Co), the average number of calls during that
period reached 5170 per day.
3.
The rare snow disaster in Qinghai-Tibet
Plateau
Beginning
in early fall of 1997, heavy snowstorms hit the Tibetan Plateau region
frequently. An excessive amount of snow fell on the Laqu,
Ali and Rikeze areas of Tibet Autonomous District and
the Yushu area in Qinghai Province. Both the duration of
and area affected by the super snowstorm were rarely seen in recorded local
history. A great number of herdsmen were besieged by the snowstorm, and an
estimated 100,000 cattle either froze or starved to death. There were
significant losses in both property and human lives during this super
snowstorm.
4.
The longest flow break in the Yellow River
The
break of water flow in Yellow River occurred every year. In
1997, however, the break in the Yellow River Basin was the most severe one
in history. The break of water flow not only occurred the earliest but also
lasted the longest (a total 226 days from February to December). The break
dramatically affected the people’s daily life, industry and agriculture.
5.
Reduced
typhoon landfall and the shortest typhoon season
In
1997, the number of typhoons generating in the Northwestern Pacific
Ocean was slightly less than the climatological
average (28 cases). The number of typhoons landing in China, however, was
significantly small (only four). The first typhoon landed on August 2 and was
much later than the climatological average (on June
25). The last typhoon making landfall was on August 29, which was also much
earlier than climatological mean. Moreover, all four
typhoons landed in August. The typhoon season was the shortest one in history.
Although there were far fewer typhoon hits than normal, the damage caused by
typhoons was still huge. In August 1997, the No.9711 typhoon landed in eastern China, and swept everything
away from the inshore provinces.On August 18, this
typhoon landed in the city of Wenlin in Zhejiang Province. The typhoon moved
north and landed again at Yingkou City in Liaoning Province on the night of August 20. There were all kinds of heavy weather such as
gales, rainstorms and severe thunderstorms along the track of the typhoon. From
August 18 to 23, the precipitation reached 50-200mm in the most parts of Zhejiang Province, the eastern part of Anhui
Province, most areas of Jiangsu Province, the City of
Shanghai, the middle part of Shandong Province, the Shandong peninsula, most
areas of Liaoning Province, the middle and western
part of Jilin Province, and the south and east part
of Heilongjiang Province. In many places, precipitation exceeded 200mm in a
short period of time.
The
No.9711 typhoon brought huge damage to the provinces and cities along the eastern
coast. The losses in agriculture, industry and the facilities of water
conservancy and electric power were very high. Many peoples were injured. Based
on incomplete statistics, the area of
stricken crop reached 5,300,000 hectares, the number of collapsed houses was
about 460,000, and the damaged houses were estimated at 1,220,000. The direct
losses were more than 35 billion yuan (RMB). In Zhejiang Province, 21,670,000 people in
75 counties suffered from the No.9711 typhoon. In the cities of Taizhou, Ningbo, Wenzhou, Shaoxin
and Hangzhou, losses were extremely
high due to the dense populations, flourishing economies and concentrated
factories in this developed region. In Zhjiang Province as a whole, there were
177,000 collapsed houses, 770,000 damaged houses, and 730,000 hectares of
stricken farmland. About 70,000 factories were forced to stop production wholly
or in part. Roads, power lines and communication lines were destroyed. The
direct losses in the whole province reached 18.6 billion yuan
(RMB).
The
No. 9711 typhoon also hit hard the inshore and inland areas of Shandong Province. The damaged farmlands
covered 2,100,000 hectares, and the number of trees brought down was over 2
million. Furthermore, 54 people died, and 105 people were reported missing. The
direct losses in the whole province were
over 13.5 billion yuan (RMB).
6. Other anomalous weather phenomena
In
1997, the Meiyu was significantly delayed with the
main rain band moving north of the Huaihe River Basin. As a result, the Yangtze River Basin suffered extremely hot
weather. According to reports from the Changjiang Daily, the
weather in the city of Wuhan, which is located in
the middle of the Yangtze River, had changed dramatically. As early as
on May 10, which is usually spring in this region, the temperature had already
reached 220C, which is the sign of summer. That was 11 days early
than climatological mean for Wuhan. The hot weather
provided favorable conditions for the spread of crop diseases. About 500,000 hectares of farmland were threatened
by leaf worms. Wuhan is known as “the Oven City” because of its
unbearable heat in summer. In the summer of 1997, however, the number of days
with temperatures higher than 360C was only 13, or 30 days less than
normal. Just when people were enjoying a pleasant summer, Wuhan turned hot in the
autumn. In the middle of October, the mean temperature was 50C
higher than normal setting a new record.
As
reported by the XINMIN EVENING NEWS, the
winter of 1997-98 was a warm winter. In December 1997, the monthly mean
temperature in Shanghai was 80C (2.1oC
higher than normal). In January 1998, the monthly mean temperature was 7.30C
(3.90C higher). Moreover, during the 1997-98 winter, there was a large
number of rainy days with a total precipitation of 102.5mm. This was about
three times the average amount. In the first ten days of January 1998,
precipitation reached 64mm in Shanghai, which was the third
highest rainfall in the same period of time in its recorded history.
