Globally elevated greenhouse gas emissions from polluted urban rivers

Cities are at the heart of global anthropogenic greenhouse gas (GHG) emissions, with rivers embedded in urban landscapes as a potentially large yet uncharacterized GHG source. Urban rivers emit GHGs due to excess carbon and nitrogen inputs from urban environments and their watersheds. Here relying on a compiled urban river GHG dataset and robust modelling, we estimated that globally urban rivers emitted annually 1.1, 42.3 and 0.021 Tg CH₄, CO₂ and N₂O, totalling 78.1 ± 3.5 Tg CO₂-equivalent (CO₂-eq) emissions. Predicted GHG emissions were nearly twofold those from non-urban rivers (~815 versus 414 mmol CO₂-eq m⁻² d⁻¹) and similar to scope-1 urban emissions in intensity (1,058 mmol CO₂-eq m⁻² d⁻¹), with particularly higher CH₄ and N₂O emissions linked to widespread eutrophication and altered carbon and nutrient cycling in urban rivers. Globally, the emissions varied with national income levels with the highest emissions happening in lower–middle-income countries where river pollution control is deficient. These findings highlight the importance of pollution controls in mitigating urban river GHG emissions and ensuring urban sustainability.