Assessment of land salinization change using remote sensing technequies in Minqin Basin, Northwest China

The Minqin Basin lies in the lower reach of Shiyang River watershed, Northwest China. There is a long history of soil salinity accumulation. The transportation and the spatial distribution of soil salinity are associated with the fluctuation of groundwater table. With the decline of groundwater table level from 0.5-3.0 m below the surface at 1960 to 15-35 m in 2004 induced by excessive extraction of groundwater, the transportation and spatial distribution of soil salinity in the profiles has changed, bringing the transformation of salinizational land in Minqin Basin. In this paper, field observation and four Landsat TM satellite images taken over a span of 14 years (1987 - 2000) are employed to determine changes of saline land by means of the techniques of Standard image enhancements, classifications, principal component. The analysis of TM images shows that the areal extent of soil salinization in the Minqin basin has been shrunk by 29.95% from 1987 to 2000 due to the decline of groundwater level. The fields observation data describing the spatial distribution of soil salinity in the profiles from 1960´s to 2000 were used to verify the results. The soil salinity content in the top 10 centimeters has reduced from 0.35-0.918% in the early 1960´s to less than 0.3% in late 1980´s. Up to now, the higher accumulation layers of salinity transported downward to 60-80 cm below the surface and the salinity-concentrating layer has moved from the top 10 cm to 60-80 cm below the surface.