Soil moisture had severe influence on
vegetation index.Using normalized difference of vegetation index (NDVI) derived from
8km NOAA/AVHRR data,the
soil moisture of surface layer of 0～10 cm and deeper layer of 10～20 cm from 1981 to 1998 was obtained from meteorological stations,and the vegetation index
sensitivity to soil moisture in Northern China was studied.The result showed that the average soil moisture as a whole had a trend of decrease in Northeastern and Northern China,while a trend of increase in Northwestern China.The responses of vegetation index to soil moisture had evident differences in different sub-regions.The sensitivity of vegetation index to soil moisture was the strongest in Northwestern China,followed by Northern China and Northeastern China.This trend was also fit for deeper layer soil moisture,but only the extent was lower than that for surface layer soil moisture.The sensitivity was also reflected in various seasons.In spring,soil moisture had strong influence on vegetation index in Northern China (P<0.05),then Northwestern China and Northeastern China,orderly.In summer and autumn,the correlations were significant at the 0.05 level,while in winter the correlation between vegetation index and soil moisture was not obvious in all of the three regions.