A Monitoring Method of Land Cover/Land Use Change in Naiman,
Inner Mongolia Autonomous Region, China Using Landsat Data
Toshiaki Imagawa, Michikazu Fukuhara, Wang Tao and Zhu Zhenda
National Institute of Agro-Environmental Sciences,
Ministry Agriculture, Forestry & Fisheries
3-1-1, Kan-nondai, Tsukuba-Shi Ibraki 305, Japan
Tel : (81)-298-38-8277 Fax : (81)-298-38-8199.
E-mail : imaga@niaes.affrc.go.jp
Abstract
Nariman Qi is located on the eastern edge of the Horqin desert and has recently experienced desertification. The desertification has progressed due to overgrazing and overcutting and fixed sand dunes began to move again in this area. In this study, we intended to develop a monitoring method of land cover/land use changes using Landsat data in order to analyze the progression of desertification. First, we were able to define the area that underwent desertification (hereafter referred to us "desertified area") using the following 3 indices; vegetation [TM 4 - TM 3)/ (TM 4 + TM 3], structure [TM 5- TM 1) /(TM 5 + TM 1)], and redness [TM 3 - TM 1) / (TM 3 + TM 1)]. We determined the yearly changes by superimposing the desertified areas identified based on data from different years. Second, we developed a monitoring method of land/cover use changes to analyze the changes to analyze the changes in the desertified areas. These methods enabled us to obtain basic information for clarifying the desertification processes.
Introduction
The term "desertification" in its technical sense has a broader meaning than simply describing the phenomenon occurring in peripheral areas of deserts. Therefore, "desertification" has been redefined in Agenda 21 as "land degradation in arid, semi-arid and dry subhumid areas resulting from various factors, including climatic variations and human activities". The term "desertification" is clearly used now to refer not only to areas surrounding deserts, but also to major food-producing areas in semi-arid and subhumid areas.
Even in East Asia, where the arid areas are not extensive, we can see that the new definition brings this problem closer to home. In particular, in eastern China, which accounts for 50% of the land and over 90% of the population of that country, climatic conditions are changing from the semi-arid regions in the north to the subtropical, subhumid areas in the south. Zhu et al. 1) estimated that desertification in China was induced by water and wind erosion, affecting 1.483 million km2 or about 15% of the land area of China.
The purpose of this study was to develop a monitoring method of land cover/land use changes using Landsat data in order to analyze the progression of desertification.
Some characteristics of desertification in Naiman
Naiman is located about 400 km NE of Beijing (Fig. 1). This semi-arid region has an annual average rainfall of 372 mm and annual average temperature of 6.4°C. Lacustrine sediments in the Quaternary are the main surface layer deposits in this region, and widely distributed sand dunes, formed in an earlier dry period, have been fixed and become covered by soil and vegetation along with the humidification of the climate. On fixed sand dunes and in the lowlands between dunes, field crops are grown, especially corn and sorghum. In addition, the grasslands in northeastern Naiman have been extensively developed.
Figure 1: Study area
Desertification has been caused by the destruction of the natural vegetation and about 1-2 m of topsoil, and begins with the movement of unconsolidated sand. In this region, a strong wind of 5 m/s (18 km/h) often blows the sand around in the spring. Landsat images have revealed wave-like patterns on the ground surface facing the dominant wind direction, with widely distributed and dunes extending from west to east. The movement of sand is inversely related to the particle size, i.e. the smaller the sand particle the greater the magnitude of movement, and annual dune movement of 5 m/yr has been observed. Furthermore, in the grassland sections we can identify points where the sand has been expanding in elliptical patterns around ponds. At present, measure have been implemented to stop the movement of sand, and there are locations in peripheral areas where vegetation has invaded.
