Divergent Responses of Multi-frequency Vegetation Optical Depth Products to Climate Variations in China

Vegetation optical depth (VOD) has been widely assessed for satellite monitoring of vegetation carbon and water status under different environmental conditions. However, abilities of multi-frequency VODs to reflect the integrated dynamics in vegetation status under changing climate are still underinvestigated, especially in China, which has experienced substantial vegetation greening since 2000. To fill this gap, this study examines 7 VOD products for their capabilities to detect vegetation status changes under climate variations from 2012 to 2022 in China. We find divergent responses of multi-frequency VODs to climate variations in China, and the retrieval frequency is the most important factor, followed by the underlying retrieval algorithms. All 7 VOD products show stronger responses to water limitations (atmospheric and soil water stress) than temperature across different plant functional types in China, suggesting high potential of VOD to track vegetation water status changes. We also find that the capabilities of VODs to represent vegetation responses to climate variations are affected by vegetation growth limitations, showing consistent responses for ecosystems dominated by either temperature or water. Most importantly, we find that VODs capture well the carry-over effects of climate on vegetation dynamics in China, with X- and C-band VODs showing stronger abilities than L-band VODs, especially for ecosystems located in China’s arid and semiarid regions. These findings address the divergent capabilities of multi-frequency VOD products to capture the vegetation responses to climate variations across China, promoting ecological applications of different VOD products in regional studies.