The use of agricultural machines for field operations is often restricted by the soil status, which is determined by the meteorological conditions several days before the operation. While a projected rise in air temperature caused by climate change may promote evapotranspiration and incur positive impacts on the use of agricultural machines, intensified rainfall may have negative effects. Here, we provide probabilistic estimates of climate change impacts on meteorological constraints on the field workability of agricultural machines in Hokkaido, Japan. Analyses based on historical meteorological data and machinery operation logs recorded at two agricultural research stations revealed that operations were concentrated on days with a smaller antecedent precipitation index (API). A simple derivative that reflects a maximum API value for conducting a certain field operation, termed threshold API, was proposed to evaluate meteorological constraints on field operations. The threshold API values for operations that were vulnerable to soil conditions (e.g., sowing and soil preparation) and/or in fields with poor drainage soil were small; therefore, this threshold should be a reasonable and quantitative measure of the meteorological constraint on field workability. Using 1 km gridded API values under historical and future climates calculated from a large ensemble dataset of daily mean air temperature and precipitation, we separated workable and unworkable days from June to October based on a threshold value of 5 mm and calculated changes in the monthly numbers of total workable days and consecutive unworkable days. While there were slight negative effects in several of the southern and central regions under a 4-K warmer future climate, positive changes prevailed in the total workable days and consecutive unworkable days in the other regions and months. The present results facilitate a probabilistic discussion of changes in agricultural calendars and suggest that climate change may extend the agricultural season in Hokkaido.

　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.