Fjölrit RALA - 05.12.1999, Side 105

RALA REPORTNO. 200
Human dimension of land degradation in Yulin area, China
Wang Changyao and Wang Quan
Institute of Remoíe Sensing Application. CAS, Beijing 100101, China
Tel: 86 10 6 491 9944 2618: Fax: 86 10 6 491 5036: E-mail: irsaglob@mimi.cnc.ac.cn
Abstract
Arid and semi-arid areas occupy one third of the total area of the worid. This vast region is rich in
natural resources. In recent times, desertification has become a world-wide phenomenon, due to hu-
man activities. China also suffers from this problem. Desertification is especially severe in the south-
eastem part of the arid and semi-arid region of the country.
In this paper, the use of remote sensing and geographical information systems for monitoring de-
sertifícation and environmental change is described and an example is given of how such information
can be used for regional planning.
Kev words: desertification, GIS, population pressure, remote sensing.
Study area and remote sensing data
In order to study the distribution and development of desertification, Yulin County has
been selected as a study area. Yulin County is situated in the northem part of Shaanxi
Province, middle course of Wuding River and the southem margin of Mao Wusu Des-
ert. The area is 128 km long ffom east to west and 124 km wide ffom north to south; a
total area of 6945 km2. The ancient Great Wall crosses over the region ffom south-
west to north-east and forms a natural dividing line. The county is located at a typical
transitional zone between the Mao Wusu desert area, which is suitable for livestock
farming, and the northem part of the Loess Plateau, an agricultural area. Concems
about the desert moving southeast-wards have been of great academic interest for a
long time. A great shelter afforestation project to control desert expansion has been
carried out in the northem part of China since 1976 (see also Xinmin and Xyue-Yong,
this issue). Since then, desertification has been reversed in some areas, but in others,
desertification has continued to move forward. Therefore, monitoring of the environ-
mental change and regional planning is needed in this region.
The research was done with the aid of remote sensing data such as Landsat TM and
SPOT images, and color inffared aerial photographs (CIR).
ANALYSIS OF DESERTIFIED LAND DISTRIBUTION USING GEOGRAPHICAL
INFORMATION
Data on the varieties of desertification types can be obtained using image processing
system to classify Landsat TM and SPOT XS data. However, the precision of auto-
matic image classification is influenced by the complexity of natural factors. In order
to improve the accuracy of the image classifícation, image processing was combined
with the use of geographical information systems (GIS).
Distribution pattern of desertified lands
A desertifícation map for the area was made with image processing and classification
data, and topographic maps (with elevation and river system data) which were entered
into the database by digitizing. These maps were combined in the GIS database
(Arc/Info). The desertified lands distribution map obtained ffom this GlS-system
shows that desertified lands are mostly distributed along banks of the Yuxi River, the
Wudao River, and the Hailiutu River. The results show that the total area of deserti-