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Disentangling contributions to past and future trends in US surface soil moisture

Abstract

Climate model simulations and various aridity indices generally indicate that summertime surface soil moisture will decrease in the continental USA as a consequence of anthropogenic climate change. However, soil moisture observations from ground probes and satellites from 2011 to 2020 indicate positive summertime trends across 57% of the continental USA. To evaluate the mechanisms driving these trends, we have developed a two-layer land surface model that predicts surface temperature and soil moisture on the basis of observed variations in precipitation, solar radiation, vapour pressure and snowmelt. Of these four model forcings, we found that internal precipitation variability explains the largest fraction of the observed soil moisture trends from 2011 to 2020. Surface air warming and the response of plants to increasing atmospheric CO2 also influence the soil moisture trends, but these effects are small at decadal timescales and partly compensate for one another. Looking forwards, our results indicate that internal precipitation variability will dictate decadal soil moisture trends and that centennial soil moisture trends will primarily depend on changes in precipitation that are currently highly uncertain.

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Fig. 1: Observed and modelled soil moisture trends for the period 2011–2020.
Fig. 2: Contributions of three forcings to soil moisture trends.
Fig. 3: Soil moisture trends induced by warming and stomatal closure.
Fig. 4: Influence of precipitation on future soil moisture trends.
Fig. 5: Coupling between temperature, VPD and soil moisture trends.

Data availability

All of the data used in this study are publicly available.

Code availability

The python code for the EMBM is available at https://github.com/Lvargaszeppetello/Two_Layer.

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Acknowledgements

L.R.V.Z. thanks the James S. McDonnell Foundation and the Harvard University Center for the Environment. A.M.T. thanks CONACyT, Fundación México en Harvard, and the Instituto de Inovación y Transferencia de Tecnología. P.H. thanks the Sahara Project.

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Contributions

L.R.V.Z. designed the EMBM, performed the analysis and wrote the first draft of the paper, and all authors contributed to the revisions. A.M.T. provided quality control validation for the soil moisture datasets and proposed measures to ensure statistical robustness. P.H. proposed the project, helped to write the paper and gave important suggestions to the section of the paper that concerns uncertainty in precipitation projections under climate change.

Corresponding author

Correspondence to Lucas R. Vargas Zeppetello.

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Supplementary Figs. 1–16 and Tables 1 and 2.

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Vargas Zeppetello, L.R., Trevino, A.M. & Huybers, P. Disentangling contributions to past and future trends in US surface soil moisture. Nat Water 2, 127–138 (2024). https://doi.org/10.1038/s44221-024-00193-x

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