The Impact of the 2019 Drought on the Terrestrial Carbon Cycle in Southwest China

Extreme drought events have strong adverse impacts on terrestrial ecosystems. However, understanding the response and recovery of vegetation to drought is still limited considering the increases in both the frequency and severity of drought events under climate change. Here, we use satellite solarinduced chlorophyll fluorescence (SIF), which is a proxy for plant photosynthesis, along with traditional vegetation indices (VIs) to investigate the impacts of the 2019 drought on vegetation growth in Southwest China, one of the major carbon sink areas in China. This drought event onset follows strong precipitation and soil moisture deficit from the spring to autumn in 2019, while the precipitation significantly exceeds the multi-year mean in July. The evolution of this drought event can be considered as a natural re-watering experiment, which provides ideal conditions for understanding the response of vegetation to re-watering during a severe drought period. Our results show that this 2019 drought has substantial impacts on the vegetation growth due to the soil moisture deficit at the critical growth stages in the spring months, while the re-watering process in July alleviates the drought damage to vegetation growth. Moreover, SIF observations provide physiologyrelated vegetation response as indicated by the larger increase in fluorescence yield ( SIFyield ) than greenness-based VIs during the re-watering period, indicating a high sensitivity of SIFyield to soil moisture. This study highlights the great potential of satellite SIF observations to monitor the timely response of vegetation growth to the changes in water conditions.