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 50,000-70,000Km
2 of land turns into desert every year. In China, the desert spreads 1560km
2 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 737,000km
2 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 47534km
2in 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 21,570.31km
2. 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 25,963.69km
2 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.
