Effect of preseason diurnal temperature range on the start of vegetation growing season in the Northern Hemisphere

Preseason temperature, the air temperature before the vegetation growing season, is the most influential factor controlling the start of the growing season (SOS) in temperate and boreal areas. Although the response of SOS to mean daily temperature (T-mean) and daily temperature extremes during the preseason period has been extensively investigated, the effect of preseason diurnal temperature range (DTR) on SOS remains largely unknown. Here, we analyze the interannual covariation of preseason DTR with SOS, determined from satellite-derived normalized difference vegetation index, over the mid and high latitudes in the Northern Hemisphere from 1983 to 2015. After using partial correlation analyses to remove the correlations between preseason DTR and preseason T-mean, cloudiness, and precipitation, we found that the partial correlation between SOS and preseason DTR was negative (i.e., that a larger preseason DTR delays SOS, and a smaller preseason DTR advances SOS) in 62.8% of the study area and positive in 37.2% of the study area. Multiple regression analysis suggested that a 1-degrees C increase in DTR could induce more than 2.5 days advance (or delay) of SOS in 45.8% (or 24.6%) of the study area. The magnitude of the sensitivity of SOS to preseason DTR was much smaller in areas with greater seasonality in temperature, which could be explained by the intensified thermal tolerance of vegetation. Further analysis showed a considerable difference in the partial correlation between SOS and preseason DTR versus that between SOS and preseason T-mean,T- indicating that preseason DTR can be used as a complementary ecological indicator to preseason T-mean in realistic modeling and predicting SOS. Although the impact of preseason DTR on spring vegetation phenology and its spatial variation are examined here, we advocate that more studies are needed to understand the physiological mechanisms governing the response of SOS to preseason DTR.