Abstract: Based on long-term records of grassland productivity and the corresponding climatic data on the Loess Plateau during 1992-2011, the change trends of temperature and precipitation during the dormancy period (November to next March) in Yunwushan area were analyzed. To reveal the response patterns of grassland productivity to dormancy climate change on the Loess Plateau, the effects of variation in climatic factors at monthly and daily scale on grassland productivity were investigated by using simple linear regression and Partial Least Squares (PLS) regression, respectively. The results indicated that: (1) in the past 20 years, mean temperature during the dormancy period in the study area has increased significantly (P<0.01), with a rate of 0.09℃·y-1, while the strongest increasing trend occurred in January and March. (2) The precipitation during the dormancy period was few, but its inter-annual variation was large. The change trend of monthly precipitation was also not significant. (3) Different impacts of temperature during different periods on productivity were found. However, overall, increased temperature during the dormancy period was negatively correlated with grassland productivity. Impacts of precipitation were negligible. (4) The negative correlations between increased dormancy temperature and grassland productivity could be properly explained by decreased snow depth, increased freezing and thawing processes, and variations in soil micro-environment caused by winter warming. The rare precipitation during the dormancy period did not exert significant effects on productivity. However, snow, as a solid form of winter precipitation, its impacts on grassland productivity need further investigations.

Key words: Loess Plateau, Grassland productivity, Dormancy period, Climate change, Hydrothermal condition