During the summer of 2022, a record-breaking heatwave-drought (DH2022) hit southern China, especially in the middle and lower reaches of the Yangtze River basin (MLYR). It caused unprecedented decline in vegetation photosynthesis, however, its impact on the regional carbon budget remains unclear. Here, we assessed the response of regional terrestrial carbon fluxes to DH2022 using the Global Carbon Assimilation System (GCASv2) by assimilating OCO-2 XCO₂ retrievals. Our results show that compared to the mean state over 2015-2021, MLYR experienced a clear reduction in carbon uptake by 45.8TgC (44.1%) during July-September. Despite impacted by the extreme event, the total annual carbon sink in southern China increased by 42.8 TgC. This is due to a warm and wet spring before summer, leading to an increase in carbon sink by 50.8 TgC and greatly compensating for the carbon losses. Also, the remaining areas except MLYR mitigated the impacts of the DH2022. Especially in Yunnan Province, the annual carbon sinks increased by 37.8 TgC. Our study provides a comprehensive assessment of land carbon dynamics in southern China under the influence of DH2022, enhancing our understanding of the impacts of climate extremes on the regional carbon cycle.
 

Drought; Heatwave; Atmospheric inversion model; Net ecosystem exchange; Terrestrial carbon sink