Divergent responses of vegetation dynamics to a changing climate through different VOD products in China

Vegetation optical depth (VOD), has been widely assessed for monitoring vegetation carbon and water status under different conditions. However, their abilities to reflect the integrated dynamics in vegetation status under a changing climate are rarely investigated, especially in China. To fill this gap, this study examines seven VOD products for their capabilities to monitor the changes in vegetation status under a varying climate from 2015 to 2021 in China, including X-, C- and L-band VOD products from AMSR-E, AMSR2, SMOS and SMAP. The results indicate that most VOD products generally show consistent responses to temperature (Ta), vapor pressure deficit (VPD) and soil moisture (SM) variations for the ecosystems with simple canopy structure, such as temperate grassland and shrublands, which are also water-limited ecosystems. Moreover, these VOD products also exhibit similar responses to a varying climate for Ta-constrained temperate forests, independent of retrieval frequencies and algorithms. For other ecosystems, however, the links between VOD and climate variables are sensitive to retrieval frequencies and algorithms. Specifically, due to the relatively high frequency, X-band VOD products can capture vegetation responses to Ta, VPD and SM stresses as the vegetation canopies respond rapidly to climate variations, especially for ecosystems located in the dry and warm regions. Furthermore, all seven VOD products, and especially X-band VOD, show high sensitivity to SM carry-over effects on vegetation dynamics, especially for temperate non-forests ecosystems. These findings help clarify the capability of different VOD products to mirror vegetation responses to a changing climate across different ecosystems in China, highlighting the importance of choosing the most appropriate VOD product as vegetation proxies in global and regional studies.