長江水系における水文干ばつによる二酸化炭素排出量の削減

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.