The MODIS data recorded from 2001 to 2010 were obtained from the data sharing infrastructure of earth system science (http://www.geodata.cn/Portal/?isCookieChecked). These data were pretreated by methods of radiation correction, geometric correction, broken line removal, and cloud removal and were then used to calculate the NDVI and land surface temperature (T
; Mao et al. 2005, 2007). On the basis of those calculations, the TVDI was determined by using the following formulae (Sandholt et al. 2002):