|
|
|
|
Arguments - Trends |
| Water |
| The
distribution of China's limited water resources is extremely uneven. The relation between
water supply and water consumption has been worsening in recent years. The groundwater
level in large parts of the North China plain has fallen due to overextraction of water
for irrigation and urban supply. Extraction of water for industrial and urban uses is
rising rapidly. Many rivers in the North typically run dry during several months of the
year. Depending on the region, China also has both drought- and flood-related water
problems. Frequent flooding along the Yellow River, ultimately caused by massive sediment
deposition in its middle and lower reaches, is a major threat to China's agricultural
sector. Water pollution is increasing. |
| Short
Description of the Problem |
| To understand China's
water problems, we have to examine the following questions: |
 |
How is
precipitation distributed in China? Has it changed in recent years? |
|
What are
China's surface water resources and how are they distributed? |
|
What are
China's groundwater resources? |
|
What are
the water consumption trends in agriculture, in industry, and in urban areas? |
 |
|
|
| Discussion |
| Precipitation
in China |
Tables
& Charts |
| Climate factors,
particularly precipitation, are critical for China's agriculture. Rainfall is very
unevenly distributed within the country: there is more than enough in the Southeast and
almost none in the West. The Xi Jiang (Pearl River) basin and delta have the highest
precipitation levels in mainland China with more than 2,000 mm per year. Very high
precipitation can be also found in Guangdong province (see Map1). From high precipitation
in the coastal provinces of the Southeast, rainfall gradually declines toward the
Northwest (see an animation
of the precipitation levels in China). An area of moderate precipitation stretches from
Yunnan in the south through the North China plain to the northwestern province of
Heilongjiang. Most of Xinjiang and Gansu provinces and most parts of Inner Mongolia,
Tibet, and Qinghai in the center are extremely dry. Average precipitation in these
provinces is usually below 200 mm per year; some areas have almost no rainfall. |
Map 1
Map 2
Figure 1
Table 1
IIASA's AEZ Project
|
A critical level of
precipitation is around 400 mm per year; below that level, rain-fed agriculture is usually
very difficult or impossible. The white areas in Map 2 show that precipiation in much of
China is below the critical level. I have analyzed how many people live in these areas
with insufficient precipitation: In the three decades between 1958 and 1988, some 3.97
billion ha in China (or 42% of the total area) had average precipitation below 400
mm; only 38 million people (or 3.3% of the population) were living in that area in 1992.
Thus, the great majority of the Chinese population has settled in areas, where
precipitation is, in principle, sufficient for agriculture.
On the other hand, that same year about 50% of China's population (589 million
people) lived in areas where average precipitation was more than 1,000 mm per year
(corresponding to some 20% of the total land). The population density in these areas was
between 280 and 324 people per square kilometer (see Figure 1 and Table 1). |
Not only does China
experience high geographical and seasonal variation in precipitation, but the rainfall
greatly fluctuates from year to year, particularly in the Northeast. While the average
precipitation in Northern China is around 600 mm per year, it can be as low as 200-300 mm
in dry years and as high as 1,300-1,500 mm in wet years. The frequent, but irregular,
occurrence of floods and droughts in Northern China is related to this extremely high
interannual rainfall variation.
IIASA's Agro-Ecological Zones (AEZ) project has analyzed in great detail the
spatial pattern of temperature profiles and precipitation in China between 1958 and 1988.
To assess China's potentially arable land the AEZ model calculated Length-of-Growing
Periods (LGP) for the whole country on a 5 by 5 kilometer grid (see in-depth description). This animation presents the changes in
LGP results for some 374,000 grid cells in China during these 31 years. One can easily see
that the thermal and precipitation conditions represented by LGPs have changed enormously
from year to year during that period. |
| One question is of
particular interest for assessing China's food prospects: Has climate change already
affected precipitation in China? In their assessment of water resources in China, the
Economic and Social Commission for Asia and the Pacific (ESCAP) cites a 1995 study by the
Nanjing Institute of Hydrology and Water Resources, in which precipitation patterns since
1956 were analyzed. They found that, despite the high spatial and temporal variation in
precipitation, the overall volume of the annual precipitation for the country
remained unchanged during that period. If climate change has already had an impact on
China, it has not shown up in the amount of precipitation. However, climate change could,
of course, affect geographical and seasonal distribution patterns (see the FAQ section). |
| Surface
water resources |
China's major rivers
are the Chang Jiang (Yangtze River), the Huang He (Yellow River), the Songhua (Sungari
Rvier), the Xi Jiang (Pearl River), the Hai He / Luan He, and the Liao He / Hiao He (see
Table 2). Their combined drainage area covers some 4.39 million square kilometers or some
46% of China's territory. More than 80% of the population and the cultivated land area are
located in the plains along the middle and lower reaches of these rivers (United Nations
ESCAP, 1997).
The Yangtze in Central China is Asia's longest river and, with its
tributaries, one of the largest navigable waterways in the world. It is the principal
transportation artery of China's industrial heartland in the lower Yangtze region
(Shanghai), and it provides irrigation water to millions of farmers in its middle region.
Its mean annual runoff is estimated at 951 billion cubic meters, equivalent to some 35% of
the country's total surface runoff. The main canal of the Yangtze has a total descent of
some 5,400 m, giving the river an outstanding hydropower potential of 268,000 MW.
This is about two-fifths of China's total hydropower potential (United Nations ESCAP,
1997). |
Table 2
|
| The Huang He (Yellow
River) in Northern and Northeastern China is the country's second longest
river, with a drainage area of about 750,000 square kilometers. Its average annual runoff
(66 billion cubic meters) is a small fraction (less than 7%) of that of the Yangtze. As
indicated by its name, the Yellow River carries huge amounts of sediments, originating
from soil erosion in the Loess Plateau in its upper and middle reaches. With an estimated
1.6 billion tons, the Yellow River has the highest sediment transport in the world. Most
of the silt load is deposited in the lower reaches (25%) and the estuary (50%); only about
25% of the sediment load is deposited in the sea. This sediment transport is the prime
cause of the disastrous floods in Northern and Northeastern China. The river floor is
rising continuously due to sediment deposits. The Chinese have tried for centuries to
confine the river to its bed by continuously raising the dykes. The Yellow River's water
level is now up to 10 meters above the surrounding land in many places. Devastating
floods occur when high precipitation raises the water level, causing the dykes to break.
This problem is exacerbated by the fact that the Yellow River has extreme
seasonal fluctuations in water flow: it can be as high as 22,000 cubic meters per second
or as low as 250 cubic meters per second. For the agricultural areas on the banks and
floodplains along the Yellow River, the continuous expansion and maintenance of dykes is
therefore essential. |
|
| According to a
comprehensive assessment of national water resources made by the Nanjing Institute of
Hydrology and Water Resources in 1995-1996 the total surface runoff of all rivers in China
was estimated at some 2,712 billion cubic meters (see Table 3). The total renewable
water resources in China are 2,812.4 billion cubic meters (equals the mean annual runoff
plus groundwater minus the interrelation between ground and surface water. see table 3).
This corresponds to a per capita runoff that is only one-third of the world's
average. The overall volume of surface water runoff is not abundant in China; however, the
real problem is its uneven spatial distribution. As can be seen from Table
3, there is very limited (and heavily fluctuating) runoff in Northern and Northeastern
China. All the rivers of the Hai He / Luan He basin, the Huai He basin, and the Huang He
(Yellow River) basin have a combined mean annual runoff of just 169 billion cubic
meters. In Southern and Southwestern China, the average annual runoff is 2,261 billion
cubic meters. In other words, Northern and Northeastern China, which have more than 58% of
the cultivated land and 44% of the population, receive only some 14% of the total surface
water runoff (see Table 4). The annual per capita water resources in Northern and
Northeastern China are in the range between 225 cubic meters in the Hai He-Luan He Basin
and 1,479 cubic meters in Northeastern China. For comparison, they range between 2,369 in
the Yangtze Basin and 31,679 Southwestern China. On a national average the annual per
capita water resources are 2,323 cubic meters. |
Table 3
Table 4
|
| Groundwater
resources |
| It is very difficult
to estimate the amount of available groundwater, especially the amount that can be safely
extracted from an aquifer. Sometimes only disastrous consequences give a clear indication
that a resource is being overexploited. In the North China Plain, the water table has been
lowered by groundwater extraction to such an extent that the surface has been lowered in
significant areas around several large cities, such as Tianjin, Beijing, and Changzhou.
Soil degradation data also indicate a decline in soil moisture. It is estimated that in
the northern part of the plain, close to Beijing, some 90% of the replenishable
groundwater is withdrawn (United Nations ESCAP, 1997). The Ministry of Geology estimates
the total amount of groundwater in China to be 828 billion cubic meters. As with surface
water, groundwater distribution does not fit well to demand patterns: Northern
China has an estimated 168.9 billion cubic meters, whereas Southern China has some 573.4
billion cubic meters (see Table 3). |
|
| Water
consumption trends |
According to the ESCAP
study mentioned above, China extracted some 519 billion cubic meters of water in 1993 (see
Table 5). Most of this water - some 406 billion cubic meters (or 78%) - was used by
the agricultural sector, mainly for irrigation. China still uses some 66% of its water for
irrigation. With 89 billion cubic meters (or 17% of the total), industry was the second
largest water user. Urban water supply systems used only 24 billion cubic meters, less
than 5% of the total water consumption.
The study also found that industrial water use was highest in the Yangtze River Basin,
which includes the city of Wuhan, one of China's major industrial centers. In this basin,
25% of all water extraction was for industry, and "only" 71% was used for
agriculture (see Table 5).
Not surprisingly, the highest urban water use was found in the Hai He-Luan He basin, which
includes the city of Beijing. Almost 9% of the total water use was for the urban water
supply. In this region, a relatively high percentage of the agricultural water use went to
the forestry, pastures, and fishery sector (29% of all water use). In Western and Central
China, almost all water (some 97%) was used for agriculture (see Table 5). |
Table 5
Table 6
|
|
Agricultural water use
While most of the water is still used for agriculture, the increase in
agricultural water consumption has been remarkably low. The Nanjing Institute of Hydrology
and Water Resources estimated that in 1980 China's agriculture used 391 billion cubic
meters of water; by 1993, water consumption had only increased to about 406 billion cubic
meters, which is less than 4%. In fact, the amount of water used for irrigation declined
by over 4%, from 358 to 343 billion cubic meters (see Table 6). |
|
Water use in industry
Between 1980 and 1993 water use in industry increased from 46 to 89 billion cubic meters,
an increase of more than 94%. Industrial water use in Southern China more than tripled,
from 4.6 to 13.9 billion cubic meters (see Table 6). |
|
Urban water consumption
The biggest increase in water use (in percentage terms) was for urban water supply.
Between 1980 and 1993, urban water supply grew by 256%, from 6.8 to 24.1 billion cubic
meters (see Table 6). |
| Flooding |
One of the greatest
water-related risks for China's food security is flooding. For instance, the great flood
of 1998 along the Yangtze and Songhua rivers not only killed some 3,000 people, destroyed
some 6 million and damaged some 12 million buildings, and required the evacuation of 240
million people - it also flooded some 4,8 million hectares of cultivated land (Kron, W.
1998). Other sources have even reported a ruined cropland area of 9 million hectares.
However, there are no obvious trends in the frequency of flooding events in China. While
some data seem to indicate that flooding is affecting larger areas (see Table 7), other
data show that the number of flood-related death in the 1990s was much lower than
in the 1930 or even the 1950s. For instance, in 1931 and 1935 two massive floods killed
some 145,000 and 142,000 people, while the 1998 flood has had about 3,000 casualties. |
Table 7 |
|
| Related Arguments |
|
Water Resources: Trends
Impact Data Quality Prediction Error Intervention Possibilities
Intervention Costs
|
|
|
Revision 2.0 (First revision published in 1999)
- Copyright © 2011 by Gerhard K. Heilig. All rights reserved. (First revision: Copyright © 1999 by IIASA.) |
|
|