Abstract: The standardized precipitation evapotranspiration index (SPEI) is a new climate drought index, which has been proved to be suited to drought monitoring and assessment at different time scales under global warming. This paper, based on SPEI, used the mean monthly temperature and monthly precipitation data from 47 weather stations in Qinghai from 1961-2012, to analyze the spatiotemporal variations of multiscalar drought risks in the growth season of crop and pasture in Qinghai in the past 52 years. The results showed there was a drying trend during the growth season, and the spatiotemporal variations of drought risks were significant. Under the background of global warming, the drying trend for the early growth stage was slightly weaker than those of the critical water demand stage and the whole growth period. As a result, the key feature of droughts during the growth season was the switch of drought from occurring in the early growth stage to occurring in the critical water demand stage. In addition, drought area showed a significant trend of further expansion. Given an average warming of 1.36 ℃ over the past 52 years, the drought risk with moderate or higher severities had increased by two times, suggesting a close relationship between the drought and climate change. Thus, climate warming may bring benefits for agriculture, but also increase the instability of agricultural production.

Key words: loss of net primary productivity, quantitative assessment, act net primary productivity, human activity, relative contribution index