RESPONSES OF VEGETATION ACTIVITY TO DROUGHT IN NORTHERN CHINA

With the third-generation normalized difference vegetation index and a multiple-timescale drought index [standardized precipitation and evapotranspiration index (SPEI)], the relationships between vegetation activity in the growing season and drought occurrences during various seasons and at different timescales were investigated in northern China. Although poorly understood previously, knowledge of these relationships is crucial for climate, vegetation and hydrological studies. Our results show that over the past three decades, vegetation activity during the growing season was significantly correlated (p < 005) with drought occurrences over 785% of northern China and highly significantly correlated (p < 0001) in semi-arid regions. In addition, there were spatially variable responses of vegetation activity to the seasonality of drought events across northern China. When drought events occurred in pre-season in the northern part of Inner Mongolia and Heilongjiang, parts of Shaanxi and Shanxi, and the western part of Xinjiang, they appear to have impacted vegetation activity, as indicated by the short and medium timescales of the drought indices (SPEI-3 and SPEI-6, with 3 and 6 months of accumulation, respectively). In the eastern part of Inner Mongolia, eastern part of Gansu and Qinghai, and southern parts of Ningxia, droughts during the growing season played a key role in vegetation growth, as recorded by the drought indices at all four timescales (SPEI-3, SPEI-6, SPEI-12 and SPEI-24). In addition, we also observed spatial variations in the responses of vegetation activity to droughts in northern China. Copyright (C) 2017 John Wiley & Sons, Ltd.