Diverse responses of vegetation phenology to changes in temperature and precipitation in Northern China

The start and end of the vegetation growing season (SOS and EOS) determine the length of the vegetation growing season and are necessary parameters to assess the primary productivity and carbon stocks of vegetation as well as the key dates to determine the start and end of soil wind erosion in arid zones. However, how SOS and EOS of different types of vegetation respond to changes in temperature and precipitation is still unclear. In this study, Moderate-resolution imaging spectroradiometer (MODIS)-normalized difference vegetation index data from 2001 to 2015 were used to estimate SOS and EOS for each vegetation type, the temperature and precipitation data recorded by the meteorological stations in the study area were used to calculate the average temperature and precipitation in 19 periods from June of the previous year to November of the following year, Spearman's rank correlation analysis was used to analyze the response relationships of SOS and EOS to average temperature and precipitation in each period. The results showed that SOS, EOS, the average timing of SOS (AvSOS) and the average timing of EOS (AvEOS) all had strong spatial heterogeneity. Precipitation is the key factor controlling SOS and EOS, an increase causing SOS to advance and EOS to be delayed, while higher temperature has the opposite effects. Overall, the average advancement rate of SOS was 0.88 day/year, the average delay rate of EOS was 0.33 day/year. From southeast to northwest, AvSOS gradually changed from 121st day to 141st day, whereas AvEOS was the opposite, advancing from 271st day to 282nd day. We divided the vegetation into 12 types in the soil wind erosion area of northern China according to latitudinal zonation and dominant vegetation species, the results avoided t a shortcoming of previous studies in which SOS and EOS were identified without distinguishing vegetation types.