Dynamic monitoring of
desertization environment using Remote Sensing technique in
Qinghai
Li Cheng Zhun
Geological Remote Sensing Centre, MOGIR , China
Abstract The paper
presents the environmental characteristics of desertization and its
distribution regularity in Qinghai, based on investigation of remote
sensing. The dynamic changes of desetization environment in the last 3
decades were studied by the means of the contrast analysis of images in
different time. Its developing trend has been discussed in both
desertification and desertization.
Introduction The
land desertization is one of important environmental disasters faced by
the people all over the world nowadays. About 50,000-70,000Km2
of land turns into desert every year. In China, the desert spreads
1560km2 every year [1] so monitoring, study and managering of
desertization environment become world wide problems. The writer made full
investigation of the present state and dynamic changes in Qinghai desert
using sensing technique in 1987-1988
The investigation was carried
out with 48 scenes of landsat images on the scale of 1:250,000 in wide
cover, little distortion, large viewing field accurate positioning and
high resolution (80%of the desert area is from TM image composed of band
2,3,4 which were acquired in the period from June to October, 1986-1987)
and a part of color infrared aerophotos at 1:50,000 scale. We set
serophotos as reference area to form different marks of ground types on
the satellite images and investigated 737,000km2 of land use,
and grassland and desert, The first remote sensing and interpretative map
of desert type in Qinghai was complied on the scale of 1:500,000. The data
of the dynamic changes of environmental factors of desertization in the
last 30 Years are counted with a method of secondary mean error using a
QJI meter, based on the different and the desert area (the accuracy is
97%) types of two origins, 15 forms and 3 active degrees in different
classes, states and counties.
The distribution and types of the
desert in Qinghai The main characteristics of distributive
regularity and types of Qinghai desert investigated with remote sensing
are:1 ) The obvious regional differences caused by climatic zones. The
desert distributes mainly in E 90°30'--105°05' , N35°30'-39°00', It covers
47534km2in the province , 6.45 percent of the total land area
2) The wide area of wind erosion. The wide area of wind erosion. The area
is 21,570.31km2. 45.38 per cent of total desert in which about
90.4 percent distributes in the centre of Chaidamu basin;3) . Wide area
and many types of windblown desert: It is about 25,963.69km2
54.62 percent of total desert, forming large sand mountains and hills. The
low flow dunes and sand flats distribute widely in salt bottom, Guobi
area, and banks of river and desert surroundings. 4) Flown dunes are
predominant . The area is 2.7 times of stabilized and semi-stabilized sand
dunes which are 14.9 and 11.9 per cent of wind deposit respectively, 5) .
the obvious regional difference of dune shape due to the effect of
regional small climate (wind speed and direction) caused by the factors of
topography and geomorphology, such as grid-shape dune caused by the wind
from different directions which are perpendicular to each other on the
west of Dulan county, pyramid dune formed by several directions of the
wind on the north of Haiyan mountain is big with 3-4 prism surfaces.
Image Characteristics of desertization environmental elements
and dynamic analysis The basic morphologic change on the ground is
the most obvious land scape indicator and main characteristic to judge the
environmental changes of desertization . it can be shown by contrast
analysis of environmental elements such as vegetation , water, desert,
oasis, salt bottom through their forms, size, color tone, texture,
location , graph relative bodies and array direction, combination, scale,
density, vegetation cover on satellite images of different period as the
direct and indirect interpretation keys.
The dynamic changes of
the desertization environment in the past 30 years are drawn from
interpreting and contrasting 50's topographic map with satellite images
acquired in 1973, 1977 and 1986:
Fig.1 Airphoto of
dune moving forward(taken in 1985). 1. Sand flat: 2
Crescent dune |
Fig.2 Farmland
surrounded by desert (taken in1985). 1. farmland; 2
Chain of crescent dune; 3 wind-croded
land. |
- Sand Dune Moves along with main Direction of the Wind and the
Desetized area is extended.
The desert buries agricultural land,
road, grassland, and the non-desert regions are turned into desert
landscape. great changes of reflectance have taken place on the
satellite images, extending white strip, sand flat, low crescent dune
along the leeward side of the main wind direction (Fig1,2). The desert
area of Chaidamu Basin is 40,000.7 Km2 which is 14.48 percent
bigger than that before[3]
- Water Level Is dropped and Lake's Area is decreased .
On
satellite images the blue water area becomes white sand land and dark
dry salt lake. In the past 30 years the water level of Qinghai lake has
been dropped 3.16m and the water area has been decreased 324km2 which is
7.0 percent of original area. Now the water level is dropping at the
rate of 10.53cm a year (fig3,4,5,6)
- The Stabilized and semi-stabilized Dunes Are in active state and
flow Dune Area is expanding
On the image, as the indicator of
stabilized and semi-stabilized dunes, the red vegetation is not only
decreasing in area but the tone turns into light red, even white. the
desert area around Qinghai lake increased by 78.16km2 in
1973-1986, spreading 6.0km2 on average every year while the
stabilized and semi-stabilized dunes decreased by 0.48km2 a
year.
Fig 3 Satellite
image of Qinghai lake in Oct 1973 |
Fig 4 Satellite
image of Qinghai lake in July 1977 |
Fig 5 Satellite
image of Qinghai lake in Sep 1986 |
Fig 6
Environmental and dynamic change of Qinghai
lake |
- Sandy Grassland Are Destroyed and Wind Erosion Is Getting
Strong.
Those-the original grassland destroyed, vegetation
degenerating, low and thin plants , and poor coverage-are caused by
human activities, such as unreasonable cultivation , too much herding,
chopping wood and building roads, etc. it also can be seen on satellite
images that the red flat turned to light red, small pieces and spots.
And they are very clear on aerophotos too. In Mugetan of Guinan, the
erosion area of grassland increases by 14.7km2 every year.
- Water resources Is not Used properly.
The original grassland
and farmland become secondary salinization, marsh because the water
level increased for over pumping water to irrigate, andthe ecologic
system being surrounded by desert is getting worse. Those are indicated
by large area of red halo and spots on images. In Geermu more than
800,000 mu of land was abandoned due to the reason as mentioned above.
The environmental characteristics of sand area and the
developing trend of desetization The forming of a desert would
have a process of generating , developing and evolution and be affected
and contrained by natural and cultural environments. By remote sensing
studying, the main charcteristics of environment of sandy area are:
- Characteristics of Gological History
Qinghai is located in
Qinghai-Xizang plateau and the desert in Qinghai has close relation with
geological development. Since Quaternary period, Ximalaya mountain and
Qinghai-Xizang plateau have been rising at a large scale from 1000m of
Neogene Period to the present 4800 m [4] and now it is still rising.
- The Conditional Characteristics of Sandy sourse
The thick
sediments of river lake facies are the main sourse of desert which is
proved by sandbody granularity, C14 measurement and contrast analysis of
heavy minerals [5] in Gonghe basin, The cyan-cyan white strips, rings
and concentric circlar features(21550km2) resulted by wind erosion from
cemetation, semi-cemen-tation sandstone, siltstone of Tertiary Period in
Chaidamu Basin have close relation with coresponding accumulation of
desert in leeward side and which is the main sourse of desert
accumulation of desert in leeward side and which is the main sourse of
desert accumulation in this basin.
- Characteristics of Climate Elements.
Qinghai desert is
chracterized by much dryness, little rainfall, low tempreature and cold,
winds almost in WN frequent and strong, and strong evaporating. These
characteristics are distinctive in zones. On the satellite images, the
kinds of vegetation (forest, bush, grassland), quality (types of
grasslands) are in parallel distribution in NE, the coverage is
decresing from ES to WN , from mountain area to sandy area of basin,
from dark red, red to cyan, cyan white in color. Those gradual changes
are the direct indicator of the the climate action, and which produces
the same influences to lake area (Fig.7).
- Characteristics of cultural Environment
The social
development and growing human activities bring strike influences to
environments. The activities of over cultivating , grazing , and wood
cutting have distrupted the land resources and led to land desetization,
grassland degeneration and environmental deterioration. The desetization
still spreads though the natural environment has been improved and the
changing velocity of farmland and water area has been slowed down
(Fig.8)mean while the reforming of environmental desertization is rather
difficult. mental deterioration the desertization still spreds though
the natural environment has been improved and the changing velocity of
farmland and water area has been slowed down (Fig.8) Mean while the
reforming of environmental desertization is rather difficult.
As
mentioned above, the dry climate and strong wind are the power to form
and develope the desert in Qinghai. The large area of loose sediments
provides enough sanday sources; The natural and potential elements are
the basis of generating and developing desert; And the human activities
are the leading factor to strengthen desertization; The development and
trend of Qinghai desertization are chracterized by spreading, sand dunes
invading into the margin of oasis, stabilizing and semi-stabilizing sand
dunes acting , the area of wind erosion expanding , water area
decreasing , environmental deterration ect.
Ecologic environment
in Qinghai is very weak (especially in north side of 35°30'). The rising
of Qinghai-Xizang plateau would influence this region furtherly.; dry
climate is going on furtherly; The environmental disruption caused by
human activities is getting worse and desertization will be intensified.
Fig 8 Dynamic changes and different
types of Qinghai Lake Conclusion The
protection of environment and ecologic balance are the first important
task tp harness the desetization. Bassed on the environmental
chracteristics of desertization and its origin, surface morphology, scale
and the relation with surrounding setting, we should enchance the regional
management and certain the reasonable usage of resources, land use and
protection by control-ling population and protecting the present forest
and grassland resources, developing and utiilizing the water resources
properly, reforming the energy structure in the countryside of desert
area. From practice, remote sensing technique is an effective tool
to investigate, study and dynamically monitor environmental deserization.
It plays an important role in forecasting the nature developing trend and
harnessing of desert. References
- Zhu Zhenda etc. An Introduction to Desert in China, Science Press,
1980.
- The research group of applications of the National Land resources
satellite data in the region of Beijing, Tianjin and Tangshan: The
Application of the National land resources satelite data, science Press
, 1988.
- Zhong Decai , Lu Jinhua: Desert Map of the people's Republic of
China (1:4000,000), Map Press, 1979.
- Geng Kuanhong : The Climate of Desert Region in China, science
Press, 1986
- Xu Shuying : Accumulation of wind sand in Gonghe Basin in Qinghai,
Desert in China, Val. No.3 1982.
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