Soil moisture dominates the severe decline in gross primary productivity during a 2023–2024 compound heatwave-drought event over the Amazon

The Amazon, the world's largest tropical forest, plays a critical role in the global carbon cycle. It has a large carbon pool and acts as a major carbon sink. However, in 2023–2024, a compound heatwave-drought event (HD2023) hit the Amazon region, resulting in extreme temperatures and soil moisture deficits, threatening the region's carbon sink capacity. Using advanced multisource satellite data and meteorological reanalysis, we quantified the impact of various climatic factors on vegetation productivity during HD2023 and analyzed its progression. Our findings showed that HD2023 led to a 530 Tg C decline in gross primary productivity and 0.003 reduction in near-infrared reflectance of vegetation. The strongest phase of the event spanned five months, causing persistently high temperatures and reduced precipitation, leading to a continuous decline in soil moisture and marked reduction in gross primary productivity. The most severe decrease in gross primary productivity occurred in January2024. The event originated in the northwest and gradually spread to the southeast. Soil moisture was the dominant factor in the decline of photosynthesis across vegetation types, whereas high solar radiation mitigated the impact of drought in evergreen broad forests and savannas. Moreover, the sensitivity of gross primary productivity to compound heatwave-drought varied across vegetation types, ranking as grassland > savanna > evergreen broad forest. This study assessed the impact of HD2023 on regional carbon flux in the Amazon. As climate projections indicate future increases in climate extremes over the Amazon, it is important to identify the drivers of this impact on the carbon cycle of the Amazon.