Glacier lagged response dominated the Himalayan water storage depletion

The depletion of terrestrial water storage (TWS) in the Himalayas has profound implications for water security, affecting billions of people downstream. However, the mechanisms behind this depletion remain highly debated. In this study, we update the water storage budget for the Himalayas, revealing that nearly all TWS depletion (−11.12 ± 1.26 Gt yr⁻¹) during 2003–2016 were from glacier mass loss (−11.69 ± 0.32 Gt yr⁻¹). The glacier evolution modeling shows that 75 ± 13% of this glacier mass loss would have occurred even if climate conditions had stabilized during this period. This lagged response to the imbalance with previous climatic conditions is modulated by the long glacier response time (the time required to reach a new equilibrium after a climatic perturbation), with a mean value of 45.6 years across the Himalayas. Our findings indicate that the observed TWS depletion is primarily a lagged response to past climate change, rather than a direct consequence of concurrent climatic conditions as previously claimed. This study reconciles existing debates by emphasizing the critical role of multi-decadal glacier response time in TWS dynamics over glaciated regions, implying that current climatic variations will continue to influence TWS changes in the coming decades, even if no further climate change.