Hydrological droughts reduce carbon dioxide emission from the Yangtze River networks.

River networks release significant amounts of carbon dioxide (CO2) into the atmosphere via gas exchanges at water-air interface, profoundly affecting the global carbon cycle. Hydrological drought, characterized by negative anomalies in river discharge, can affect the transport and decomposition of organic matter, thereby significantly impacting riverine CO2 emissions. However, the extent to which hydrological droughts affect CO2 emission fluxes remains unanswered. In this study, we developed a framework to quantify the impact of hydrological droughts on CO2 emissions from the Yangtze River networks. We found that hydrological droughts led to approximately 33 % reduction in CO2 evasions in Yangtze River networks compared with non-drought periods. Moreover, the reduction in CO2 emissions across all stream orders of rivers showed significantly positive correlations to drought severity (p < 0.001). Notably, the emission reduction primarily resulted from river width contraction, which diminished the water-air interface area and consequently limited CO2 evasion. These findings highlight the importance of deepening our understanding of the impact of hydrological droughts on riverine CO2 emissions.