Strong Regulation of Precipitation on Spring Phenology in the Tibetan Plateau from 1982 to 2008
Thursday, 18 December 2014
Understanding climatic controls on the spring phenology in the Tibetan Plateau (TP) is crucial to predict ecosystem responses to climate change, but is generally limited, partly due to uncertainties in different phenology datasets. In this study, we investigated the associated climatic controls on the start of growing season (SOS) derived from three widely-used satellite NDVI datasets in the TP grasslands, together with a satellite-derived freeze-thaw dataset and in-situ meteorological observations. Our results show that the SOS of TP grasslands is generally negatively correlated with spring temperature (Ta) from 1982 to 2008 (R<-0.40, p<0.05), while the temperature effects are strongly regulated by spring precipitation (P), with the interaction of temperature and precipitation effects varying across the TP areas. In the steppe-dominated western TP region (spring Ta=-3.3 oC, P=23.0 mm), P is increasingly positively correlated with SOS during the period of 1996-2008, i.e. more precipitation tends to delay spring onset. This is likely because a strong increasing precipitation trend (0.49 mm yr-1, p<0.05) in this area gradually relieves the spring water deficit, and more precipitation is generally associated with low heat. However, in the relatively humid eastern region dominated by meadow (spring Ta =-3.5 oC, P=72.9 mm), P becomes less positively correlated with the SOS. This is likely caused by increasing spring water deficit due to a strong warming trend (0.045 oC yr-1, p<0.05), and a slight decline in spring P (-0.071 mm yr-1, p>0.1). Similarly, the whole TP generally shows an advancing trend in spring thawing (0.35 day yr-1, p<0.05), which has an increasingly positive effect on spring onset, especially in the meadow areas. Our results demonstrate the strong regulation of precipitation on TP vegetation spring phenology, which may become more important for understanding vegetation response to climate change with continuing warming.