Vegetation green up under the influence of daily minimum temperature and urbanization in the Yellow River Basin, China

Climate conditions are the major driving factors of vegetation phenology. However, there is limited effort to monitor dynamics of vegetation phenology and its responses to climate change and urbanization. Using NDVI data from 1982 to 2015, this study investigated the spatiotemporal change of spring green-up date (GUD) across the Yellow River Basin (YRB) and estimated the possible effects of different climatic factors on it. Additionally, the urban-rural differences in GUD and its linkage to spring land surface temperature (LST) for YRB's major cities over 2001-2015 were investigated. The results showed that the GUD significantly advanced at a rate of 0.42 days yr(-1) and delayed spatially from southeast to northwest. The interannual variations in regionally averaged GUD were driven mainly by preseason min-temperature (T-min). Spatially, the effect of preseason T-min was strongest in the central and western region. The confounding effects of preseason maximum temperature (T-max) and precipitation jointly affected the GUD, while insolation had a weak impact on GUD. Moreover, the sensitivity of GUD to preseason T-min and precipitation weakened with an increasing mean annual preseason precipitation gradient, but the sensitivity to preseason T-max was gradually enhanced. Furthermore, the difference in the GUD between urban and rural areas presented a significant logarithmic relationship with the distance away from the urban center, and it was strongly related to the regional LST. Our findings confirmed the importance of T-min and urbanization in regulating changes in GUD and further suggested that LST should be considered to develop an improved model of GUD under future climate change and urban development.