Hua et al. (2025) Divergent water controls on vegetation productivity across drylands of the contiguous United States

Identification

• Journal: Journal of Hydrology
• Year: 2025
• Date: 2025-12-27
• Authors: Tiantian Hua, Mengyun Sun, Lixin Wang
• DOI: 10.1016/j.jhydrol.2025.134881

Research Groups

Department of Earth and Environmental Sciences, Indiana University Indianapolis, Indianapolis, IN 46202, USA

Short Summary

This study quantifies the relative importance and nonlinear impacts of soil moisture (SM) and vapor pressure deficit (VPD) on gross primary productivity (GPP) across drylands of the contiguous United States. It reveals that SM is a stronger control than VPD, with varying critical soil depths and threshold-like responses along aridity gradients.

Objective

• To quantify how both the mean state and daily variability of soil moisture (SM) and vapor pressure deficit (VPD) shape gross primary productivity (GPP), stratified by aridity class and SM depth, across drylands of the contiguous United States.

Study Configuration

• Spatial Scale: Site-level observations across contiguous U.S. drylands.
• Temporal Scale: Multi-year daily observations.

Methodology and Data

• Models used: XGBoost–SHAP framework
• Data sources: Site data from the National Ecological Observatory Network (NEON) and AmeriFlux.

Main Results

• Soil moisture (SM) exerts a stronger influence on gross primary productivity (GPP) than vapor pressure deficit (VPD) in drylands.
• The mean states of SM and VPD play a dominant role in regulating GPP, whereas their daily variability exerts smaller and more context-dependent effects.
• Critical SM depth varies with aridity: 0–0.1 m SM is most influential in arid and semi-arid zones, while 0.1–0.3 m SM becomes more critical in dry sub-humid zones.
• Ecosystems are primarily water-limited in arid and semi-arid zones but become increasingly energy-limited (temperature, radiation) towards dry sub-humid zones.
• Threshold-like transitions were observed:
  • 0–0.1 m SM shifts from negative to positive effects on GPP at approximately 0.14–0.25 m³/m³ (volumetric water content).
  • VPD shifts from weakly positive to negative effects on GPP at approximately 770–1660 Pa.
  • Drier regions exhibit lower SM thresholds and higher VPD thresholds.

Contributions

• Provides a comprehensive quantification of the relative importance and nonlinear impacts of SM and VPD (including their mean state and daily variability) on GPP across dryland aridity gradients and different soil depths.
• Highlights the spatial heterogeneity and threshold-driven nature of dryland productivity responses to hydrometeorological conditions.
• Offers key insights into ecosystem functioning under increasing water stress and future climate scenarios.

Funding

Not specified in the provided text.

Citation

@article{Hua2025Divergent,
  author = {Hua, Tiantian and Sun, Mengyun and Wang, Lixin},
  title = {Divergent water controls on vegetation productivity across drylands of the contiguous United States},
  journal = {Journal of Hydrology},
  year = {2025},
  doi = {10.1016/j.jhydrol.2025.134881},
  url = {https://doi.org/10.1016/j.jhydrol.2025.134881}
}