Wang et al. (2026) Spatiotemporal dynamics of global surface and rootzone soil moisture: a comprehensive assessment from dominant factors, impact pathways, and deficit probability

Identification

• Journal: Geoderma
• Year: 2026
• Date: 2026-03-21
• Authors: Zijun Wang, Rong Wu, Yangyang Liu, Chenfeng Cui, Na Zhao, Yinghan Zhao, Zhongming Wen, Zhixin Zhang, Wei Zhang
• DOI: 10.1016/j.geoderma.2026.117783

Research Groups

• College of Water Resources and Architectural Engineering, Northwest A&F University, Yangling, Shaanxi, China
• State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan, China
• College of Grassland Agriculture, Northwest A&F University, Yangling, Shaanxi, China
• State Key Laboratory of Resources and Environmental Information System, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, China

Short Summary

This study comprehensively assessed global surface and root-zone soil moisture dynamics from 2001 to 2021, identifying atmospheric water demand as the primary driver of aridity and revealing vegetation's mediating role in climate-soil moisture interactions, with precipitation, SPEI, and vegetation dynamics as key deficit risk factors.

Objective

• To characterize the spatiotemporal dynamics of surface soil moisture (SMsurf) and root-zone soil moisture (SMroot) under distinct climatic regions.
• To measure the relative contributions of climate change and vegetation greening to SM fluctuations using Random Forest coupled numerical simulation experiments.
• To elucidate both direct and indirect pathways through which vegetation dynamics and climatic variables regulate SM changes based on structural equation models.
• To assess the sensitivity thresholds of SM responses to multifactorial drivers under coupled environmental interactions based on copula functions.

Study Configuration

• Spatial Scale: Global, with data resolutions ranging from 0.05° to 0.5° and bilinearly interpolated to a uniform 0.25° spatial resolution.
• Temporal Scale: Monthly, covering the period from January 2001 to December 2021 (21 years).

Methodology and Data

• Models used:
  • Theil-Sen slope estimation and Mann-Kendall (MK) test for trend analysis.
  • Random Forests (RF) for numerical simulation experiments to separate absolute contributions of variables.
  • Partial Least Squares Structural Equation Modeling (PLS-SEM) to investigate direct and indirect effects and causal relationships.
  • Copula functions (Gauss, Clayton, t-, Frank, Gumbel) to depict and model tail dependencies and calculate joint conditional probabilities of SM deficits.
  • Seasonal and Trend decomposition using Loess (STL) for time series decomposition.
• Data sources:
  • K¨oppen-Geiger climate classification map (0.5° spatial resolution, 1980–2016).
  • Global Land Evaporation Amsterdam Model (GLEAM) SM dataset (0.1° spatial resolution, monthly, 2001–2021) for surface (0–10 cm) and root-zone (10–250 cm) SM.
  • Global Land Data Assimilation System (GLDASNOAH025M) SM data (0.25° spatial resolution, monthly, 2001–2021) for four depth layers (0–10 cm, 10–40 cm, 40–100 cm, 100–200 cm).
  • ERA5-Land reanalysis dataset (0.25° spatial resolution, monthly, 2001–2021) for four depth layers (0–7 cm, 7–28 cm, 28–100 cm, 100–289 cm).
  • Global Land Surface Satellites (GLASS) Leaf Area Index (LAI) (0.25° spatial resolution, 8-day interval, aggregated to monthly).
  • Global OCO-2 SIF dataset (GOSIF-Gpp) (0.05° spatial resolution, monthly, 2001–2021).
  • GLDASNOAH025M meteorological data (0.25° spatial resolution, monthly) including downward longwave radiation (Lrad), downward shortwave radiation (Srad), atmospheric pressure, specific humidity, precipitation (Pre), atmospheric water demand (Ep), near-surface air temperature at 2 m (Temp), and wind speed (WS). Relative humidity (RH) and Vapor Pressure Deficit (VPD) were derived.
  • Global SPEI database (0.5° spatial resolution, 12-month timescale).

Main Results

• SMsurf and SMroot exhibited broadly similar global spatial patterns, but their fluctuation periods, amplitudes, and frequencies differed markedly in hotspot regions. SMsurf showed greater fluctuations than SMroot.
• Numerical simulations revealed that atmospheric water demand (Ep) was the primary cause of aridity in both global SMsurf and SMroot, with effects of 8.9 × 10⁻⁵ m³/m³/year and 7.5 × 10⁻⁵ m³/m³/year, respectively.
• Vegetation greening and precipitation exerted strong but contrasting effects on SMsurf and SMroot. Globally, LAI and total radiation (Rad) had positive effects on SMsurf but negative effects on SMroot, while precipitation (Pre) showed the opposite pattern.
• Partial Least Squares Structural Equation Modeling (PLS-SEM) indicated that vegetation primarily mediated the indirect effects of climate on SM. For example, in the Boreal region, vegetation was the main mediating variable for Pre, Temp, and Rad's influence on SM.
• Copula functions identified precipitation, Standardized Precipitation Evapotranspiration Index (SPEI), and vegetation dynamics (LAI, SIFGpp) as the primary risk factors for both SMsurf and SMroot deficits. Under the same conditions, the conditional probability of SM deficits induced by these factors was 2–3 times higher than that associated with other drivers.
• SM exhibited the greatest sensitivity to various factors in the Arid region, followed by Temperate and Tropical regions. Precipitation deficit was consistently the highest risk factor for SM depletion across all climatic zones.

Contributions

• Provided a comprehensive assessment of spatiotemporal characteristics, dominant factors, impact pathways, and deficit probability for global surface and root-zone soil moisture.
• Offered the first quantitative assessment of the probability of soil moisture loss under different stress scenarios.
• Advanced the mechanistic understanding of multilayer soil moisture dynamics under a changing climate.
• Provided a robust scientific basis for improving global hydrological assessments and water resources management.

Funding

• National Natural Science Foundation of China (No. 42477522, No. U1203182, No. 51279166)
• Science and Technology Plan Project of the Tibet Autonomous Region (XZ202501ZY0045)
• Key R&D Plan of Shaanxi Province (No. 2024SF-YBXM-621)
• State Key Laboratory of Resources and Environmental Information System
• Open Research Fund of Key Laboratory of Digital Earth Science, Chinese Academy of Sciences (No. 2022LDE003)

Citation

@article{Wang2026Spatiotemporal,
  author = {Wang, Zijun and Wu, Rong and Liu, Yangyang and Cui, Chenfeng and Zhao, Na and Zhao, Yinghan and Wen, Zhongming and Zhang, Zhixin and Zhang, Wei},
  title = {Spatiotemporal dynamics of global surface and rootzone soil moisture: a comprehensive assessment from dominant factors, impact pathways, and deficit probability},
  journal = {Geoderma},
  year = {2026},
  doi = {10.1016/j.geoderma.2026.117783},
  url = {https://doi.org/10.1016/j.geoderma.2026.117783}
}