Preseason drought controls on patterns of spring phenology in grasslands of the Mongolian Plateau

Climate change has led to frequent drought events on the Mongolian Plateau; however, the pattern of preseason drought impacts on the start of the growing season (SOS) in grasslands is unclear. To determine how preseason drought controls the SOS in Mongolian Plateau grasslands, we quantitatively studied the sensitivity characteristics of the standardized precipitation evapotranspiration index-3 (SPEI-3) to the SOS and spatiotemporal differences based on meteorological and remote sensing datasets. The results show that: 1) in the past 34 years, the regions with a trend for earlier SOS in Mongolian Plateau grasslands were mainly distributed in the typical steppe region, accounting for 30% of the total area, while 13% of the pixels showed a delayed trend, mainly occurring in desert steppes, and the remaining 57% of the pixels did not show a significant change (P < 0.05); 2) preseason drought had an obvious inhibitory effect on grassland SOS, especially on typical steppes; 3) according to the SPEI-3, in the Mongolian Plateau grasslands, the SOS was advanced by 11 days when the SPEI-3 < 0.63, but the SOS was delayed by 3 days when the SPEI-3 > 0.63; and 4) the sensitivity of the SOS to preseason drought significantly decreased from 1982 to 2015 in Mongolian Plateau grasslands. Our results can be used to improve the interpretation of the SOS response to drought in the land surface model.