Sun et al. (2026) Progressive groundwater decoupling may drive a shift toward shallower and faster terrestrial water cycling

Identification

• Journal: Hydrology and earth system sciences
• Year: 2026
• Date: 2026-08-19
• Authors: Aoqi Sun, Wenjie Xu, Enze Ma, Hua Yuan, Chao Yang
• DOI: 10.5194/hess-30-5215-2026

Research Groups

• School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai, China
• College of Soil and Water Conservation Science and Engineering, Northwest A&F University, Yangling, China

Short Summary

This study investigates the impact of sustained increases in evapotranspiration (ET) demand on groundwater connectivity and terrestrial water cycling. The results suggest that progressive groundwater decoupling drives a shift toward shallower and faster pathways.

Objective

• To examine how sustained hydrologic stress influences subsurface connectivity and groundwater buffering capacity.
• To investigate whether increased ET demand can reorganize internal water age structure and lead to a shift toward shallower and faster terrestrial water cycling.

Study Configuration

• Spatial Scale: Hillslope scale, representing the fundamental hydrologic unit where vertical and lateral processes interact.
• Temporal Scale: 20-year simulation period with hourly time steps.

Methodology and Data

• Models used: ParFlow–CLM (Kollet and Maxwell, 2008) for integrated hydrologic modeling and particle tracking using EcoSLIM (Maxwell et al., 2019).
• Data sources: Meteorological data from the Little Washita watershed in Oklahoma, USA.

Main Results

• Under baseline conditions, ET and outflow exhibit coexisting young and older age components.
• Following late-summer groundwater drawdown, intermediate-age contributions weaken, producing a temporary age gap that separates shallow and deep sources.
• Enhanced ET forcing through warming (+1 °C), greening (MaxLAI + 50 %), and their combination amplifies seasonal groundwater depletion, leading to deeper water tables and larger storage losses during the late growing season.

Contributions

• This study provides new insights into the impact of sustained hydrologic stress on groundwater connectivity and terrestrial water cycling.
• The results suggest that progressive groundwater decoupling drives a shift toward shallower and faster pathways, challenging the traditional view of groundwater as a critical buffer against drought.

Funding

• This research was supported by the National Natural Science Foundation of China (Grant No. 91637206) and the Guangdong Provincial Key Laboratory for Climate Change and Natural Disaster Research (Grant No. 2021KYZD001).

Citation

@article{Sun2026Progressive,
  author = {Sun, Aoqi and Xu, Wenjie and Ma, Enze and Yuan, Hua and Yang, Chao},
  title = {Progressive groundwater decoupling may drive a shift toward shallower and faster terrestrial water cycling},
  journal = {Hydrology and earth system sciences},
  year = {2026},
  doi = {10.5194/hess-30-5215-2026},
  url = {https://doi.org/10.5194/hess-30-5215-2026}
}