Temporal variation characteristics in the association between climate and vegetation in Northwest China.

Northwest China has undergone notable alterations in climate and vegetation growth in recent decades. Nevertheless, uncertainties persist concerning the response of different vegetation types to climate change and the underlying mechanisms. This study utilized the Normalized Difference Vegetation Index (NDVI) and three sets of meteorological data to investigate the interannual variations in the association between vegetation and climate (specifically precipitation and temperature) from 1982 to 2015. Several conclusions were drawn. (1) R (relationship between Growing Season NDVI and precipitation) decreased significantly across all vegetation, while R (relationship between Growing Season NDVI and temperature) showed an insignificant increase. (2) Trends of R and R exhibited great variations across various types of vegetation, with forests displaying notable downward trends in both indices. The grassland exhibited a declining trend in R but an insignificant increase in R, while no significant temporal changes in R or R were observed in the barren land. (3) The fluctuations in R and R closely aligned with variations in drought conditions. Specifically, in regions characterized by VPD (vapor pressure deficit) trends less than 0.02 hpa/yr, which are predominantly grasslands, a rise in SWV (soil water volume) tended to cause a reduction in R but an increase in R However, a more negative trend in SWV was associated with a more negative trend in both R and R when the VPD trend exceeded 0.02 hPa/yr, primarily in forests. Our results underscore the variability in the relationship between climate change and vegetation across different vegetation types, as well as the role of drought in modulating these associations.