Assessment of a potential regime shift in global terrestrial water storage

Tipping points have been identified in several components of the Earth system, raising concerns about abrupt and potentially irreversible changes under climate change. A recent analysis of GRACE satellite data reveals a sudden and unprecedented decline in terrestrial water storage (TWS) during 2015–2016, coinciding with a major El Niño–Southern Oscillation (ENSO) event (Rodell et al. 2024). This decline suggests a recent net drying of the land and raises the hypothesis of a regime shift in the global terrestrial water system. Potential mechanisms include enhanced evapotranspiration, intensifying drought frequency and severity, and land–atmosphere feedbacks. Early warning signals, such as increased autocorrelation and variance observed prior to the decline, support this hypothesis.

To evaluate the significance and rarity of the observed transition, we develop a detection methodology and apply it to both observational estimates and climate model simulations. By analysing fully coupled pre-industrial control simulations, historical simulations, and AMIP-style experiments with prescribed sea surface temperatures, we aim to disentangle the roles of anthropogenic climate change and specific modes of climate variability (e.g., ENSO) in driving this transition. Furthermore, we explore the potential for transitions to alternative states in global TWS. Our work establishes a framework for understanding abrupt changes in TWS and their implications for the terrestrial water cycle in a warming climate.

References

Rodell, M., Barnoud, A., Robertson, F.R. et al. An Abrupt Decline in Global Terrestrial Water Storage and Its Relationship with Sea Level Change. Surv Geophys 45, 1875–1902 (2024). https://doi.org/10.1007/s10712-024-09860-w