Low and contrasting impacts of vegetation CO<sub>2</sub> fertilization on global terrestrial runoff over 1982–2010: accounting for aboveground and belowground vegetation–CO<sub>2</sub> effects

Abstract. Elevation in atmospheric carbon dioxide concentration (eCO2) affects vegetation water use, with consequent impacts on terrestrial runoff (Q). However, the sign and magnitude of eCO2 effect Q are still contentious. This is partly due to eCO2-induced changes use having opposing responses at leaf scale (i.e., water-saving caused by partially stomatal closure) canopy water-consuming induced foliage cover increase), leading highly debated conclusions among existing studies. In addition, none studies explicitly account for plant rooting depth that overwhelmingly found experimental observations. Here we develop an analytical ecohydrological framework includes effects leaf, density, characteristics attribute detect signal via feedbacks over 1982–2010. Globally, a very small decrease during 1982–2010 (−1.7 %). Locally, find positive trend (p < 0.01) Q–eCO2 response along resource availability (β) gradient. Specifically, be negative reduces Q) low-β regions (typically dry and/or cold) gradually increases high-β areas warm humid). Our findings suggest minor role global 1982–2010, yet highlight semiarid arid may further reduce limited there.