Precipitation as a control of vegetation phenology for temperate steppes in China

Using the NDVI ratio method, the authors extracted phenological parameters from NOAA-AVHRR NDVI time-series data (1982-2008). The start of the growing season (SOS) and the date of maximum NDVI (Peak-t) correlated significantly with the mean annual precipitation along regional gradients of the steppes. Along the south transect (located at a lower latitude with a higher annual mean temperature) there was a positive correlation between the end of the growing season (EOS) and the mean annual precipitation along precipitation gradients (R-2 = 0.709, p < 0.0001). However, along the north transect (located at higher latitude with lower annual mean temperature), the EOS was slightly negatively related with the mean annual precipitation (R-2 = 0.179, p < 0.1). There was positive correlation between the length of the growing season and the annual precipitation along two transects (R-2 = 0.876, p < 0.0001 for the south transect; R-2 = 0.290, p < 0.01 for the north transect). Thus, for the Inner Mongolian steppe, it is precipitation rather than temperature that determines the date of the SOS.