VCI-based Analysis of Spatio-temporal Variations of Spring Drought in China from 1981 to 2015

Drought is one of the most serious natural disasters. In this study, based on NOAA/AVHRR meteorological satellite data from 1981 to 2015, the spatial and temporal characteristics of spring drought in China were analyzed by using vegetation status index (VCI) as drought monitoring index, frequency analysis, trend rate analysis, anomaly index analysis and Mann-Kendall mutation test. The results show that China is a high-incidence area of spring drought, but most of the areas are mainly light and moderate drought. The heavy drought areas are concentrated in southern Tibet, Sichuan Basin, Tarim Basin and the surrounding areas of Qaidam Basin. The frequency of drought is obviously different in different regions. The frequency of spring drought is relatively high in the northern and southern regions which are greatly affected by monsoon. The frequency of spring drought is relatively low in the northwest and Qinghai-Tibet regions which are less affected by monsoon, except in Xinjiang, northern Inner Mongolia and southern Tibet. During 1981 - 2015, the spring VCI in all parts of China showed an overall upward trend, that is, drought in most regions tended to ease. Moreover, the trend was a wavelike increasing trend rather than a one-way change and could be divided into 4 phases: 1) a slow increasing phase from 1981-1990, 2) an intensive fluctuating phase from 1991-2000, 3) a steady increasing phase from 2001-2010, and 4) a slow decreasing phase after 2010. Mann-Kendall analysis further suggested that the VCI sequence of the Spring Festival in China was on the rise, and the changes in the south, northwest and Qinghai-Tibet regions reached significant levels. The time point of mutation in the South was 2000, and that in the northwest and Qinghai-Tibet regions was 1992.