The Taklimakan and Gobi deserts and the Loess Plateau in China and Mongolia are generally recognized source areas for Asian dust. However, dust emissions depend on meteorological factors such as air pressure and land surface conditions, and precise information on land surface conditions in the dust source areas and the frequency of dust events in Japan is lacking. In this study, interannual changes of land surface conditions in the springtime since 2000 were examined in a target source region (35°N-50°N, 100°E-120°E). Back trajectory analysis results showed that most dust trajectories of the past 10 years mainly followed three routes passing over this target region. Both the number of Asian dust events observed in Japan and the area with a threshold wind speed U_t of <10 m s^-1 in the target region significantly decreased after 2000. Further, the area of U_t < 10 m s^-1 and the number of events were significantly correlated. These results may reflect a decrease in the bare land surface area, which is associated with dust outbreaks.