Characterizing Spatial Patterns of the Response Rate of Vegetation Green-Up Dates to Land Surface Temperature in Beijing, China (2001-2019)

The phenology indicator of vegetation green-up dates (GUD) is prone to being affected by changes in temperature. However, the influencing degree of urbanization-induced temperature warming on vegetation GUDs among different vegetation species along the urban-rural gradient remains inadequately described. In this study, based on the long-term (2001-2019) satellite-derived vegetation GUDs and nighttime land surface temperature (LST) of forests, grasslands, and croplands along the urban-rural gradient with Beijing (China) as a case study area, the responses of vegetation GUDs to temperature changes were quantitatively analyzed, taking into account the vegetation types and distances away from the urban domain. The results show that (1) long-term GUDs and LST are significantly negatively correlated, characterized by a weaker significant correlation near the urban area when compared with its surrounding areas, with the greatest absolute linear correlation coefficients (r) happening at rings 32 km (r(max) = 0.93, forests), 20 km and 48 km (r(max) = 0.83, grasslands), and 34 km (r(max) = 0.82, croplands), respectively; (2) the magnitude of change in GUDs over the past 19 year (2001-2019) are significantly positively correlated with these in LST near the urban area, demonstrating a distance-decay trend, with the greatest advance in GUDs occurring at the ring nearest the urban area, by about 20 days (forests), 24.5 days (grasslands), and 15.6 days (croplands), respectively; (3) the spatial pattern of the response rate of GUDs change to LST change (days K-1) also showed a declining trend with distance, with GUD advanced by 6.8 days K-1 (forests), 7.5 days K-1 (grasslands), and 4.9 days K-1 (croplands) at the closest ring to the urban, decreasing to about 2.3 days K-1 (48 km), 4.1 days K-1 (18 km), and 1 day K-1 (18 km), respectively, indicating a notable influence of temperature warming on vegetation GUDs near the urban domains.