Groundwater storage change represents as a significant source of atmospheric CO<sub>2</sub> in China

<p>Recent studies show that groundwater depletion is an unreported source of atmospheric CO₂ through bicarbonate reactions in the groundwater released from aquifer. However, the depletion can be mitigated or offset by recharge, and thus the contrasting roles of depletion and recharge on carbon cycle remain unclear at a national scale. Here, we extend previous studies to use the satellite–derived groundwater storage change (GWSC) and substantial in situ measurements of the bicarbonate ion concentration (BIC), for the first time evaluation of GWSC–induced CO₂ emission/sequestration in China. Results show that the GWSC represents as a significant source of atmospheric CO₂ in China, with a net CO₂ emission rate of 2.1±2.3 Mt/yr, which is larger than 15% of the emission sources listed in China Carbon Emission Accounts and Datasets. Besides, emission and sequestration induced by groundwater storage (GWS) decrease and increase is also significant, with a rate of 3.9±1.1 Mt/yr and 1.8±1.2 Mt/yr, respectively. Notably, we also find that China’s stricter groundwater measures can contribute a total reduction of 5.3 Mt CO₂ emission in the major overdraft areas by 2025. Despite of notable uncertainties, this study highlights the unneglectable contributions of GWSC to atmospheric CO₂ emission and sequestration at a national to global scale.</p>