Research Background
Under the combined influence of global change and human activities, groundwater systems are facing increasingly severe pressures. Particularly in semi-arid regions, uneven spatiotemporal distribution of precipitation, ecological restoration that alters the underlying surface structure, and the substantial vadose zone’s resistance to downward water infiltration have made questions such as “when and how groundwater is recharged, and what the magnitude of that recharge is” central scientific issues. The hilly–gully region of the Loess Plateau is a quintessential ecologically fragile area in China; ecological restoration initiatives like returning farmland to forest and reclaiming gully land have markedly reshaped slope–gully hydrological processes, yet long-term, direct field observations of their impacts on groundwater recharge remain scarce.
Based on this, the research team led by Professor Yunqiang Wang at the Institute of Earth Environment, Chinese Academy of Sciences, selected the Gutun watershed in Yan’an City, Shaanxi Province, as their study site and conducted a seven-year-long series of continuous field observations. The resulting findings were published in Ecological Engineering. The study systematically monitored precipitation, soil moisture, groundwater levels, and stable isotopes in multiple water bodies. The results revealed that extreme precipitation events—both at the event scale and on an annual timescale—significantly enhanced groundwater recharge in the ecologically restored catchment through preferential flow pathways and rising groundwater levels. This provides crucial empirical evidence for understanding the rapid hydraulic connectivity among precipitation, soil water, and groundwater within the thick unsaturated zone of the Loess Plateau, and offers important scientific guidance for sustainable groundwater management in the context of ecological restoration projects.
Figure 1. Location of the study area and sampling points.
Research Methodology
The research team, leveraging the National Field Scientific Observation and Research Station for the Critical Zone of the Loess Plateau in Shaanxi, conducted continuous field monitoring over a seven-year period (2017–2023) in the Gutun watershed of Yan’an.
Monitoring system: covers meteorological stations, surface water, soil water, and groundwater level monitoring;
It is worth noting that the research team used the LI-2100 Automated Vacuum Water Extraction System (Beijing Lijia United Technology Limited) to extract soil water from samples. This instrument operates on the principle of ultra‑low‑pressure vacuum distillation and freezing, enabling not only highly efficient (98%) recovery of soil water but also rigorous control over the extraction process, thereby minimizing isotopic fractionation caused by evaporation and ensuring the accuracy of hydrogen and oxygen isotope analyses.
Figure 2. Vertical distribution of soil moisture in the 4000 cm soil profile on south- and north-facing slopes.
Figure 3: Monthly soil moisture dynamics in a 4000 cm soil profile, July 2021 – March 2022
Figure 4. Time series of the groundwater table during the precipitation event (a), and the relationship between groundwater table fluctuations and various influencing factors (b–g).
Figure 5. Time-dependent variation (a) and the significant difference in groundwater table levels between precipitation years (b).
Figure 6. Soil water content (P) pattern along the slope length within the 0–500 cm soil profile after a rainfall event.
Research Results
(1) Extreme precipitation events primarily trigger deep hydraulic connectivity between the unsaturated and saturated zones via preferential flow pathways.
(2) At the event scale, low-intensity, long-duration precipitation is more conducive to groundwater recharge.
(3) Annual scale: Recharge is enhanced during wet years and diminished during dry years;
(4) Slope‑surface soil moisture: Deep soil on the slope experiences long-term moisture deficits.
(5) Ecological restoration effect: increased water consumption on slopes and enhanced recharge to gullies;
Conclusion
This study, based on long-term continuous observations, elucidates the key mechanisms governing groundwater recharge in ecologically restored watersheds within the loess hilly–gully region at both event‑scale and annual scales. It demonstrates that extreme precipitation events can significantly enhance groundwater recharge via preferential flow and slope‑gully hydrological linkages; however, they also exacerbate spatial heterogeneity in the recharge process and pose certain eco‑hydrological risks. These findings not only deepen our understanding of the coupled “precipitation–soil water–groundwater” processes in semi‑arid regions but also provide crucial scientific evidence for groundwater resource management, soil and water conservation, and regional sustainable development in the context of ecological restoration. Future research should further strengthen long-term continuous monitoring and mechanistic investigations to better support the evaluation of ecological restoration outcomes and the sustainable management of groundwater resources.
Journal published in: Ecological Engineering [Impact Factor: 12.4]
Research institutions: Institute of Earth Environment, Chinese Academy of Sciences; Northwestern Polytechnical University; Xi’an Jiaotong University, among others.
Study site: Gutun Basin, Yan’an, Shaanxi Province
Equipment used: LI-2100 Automated Vacuum Water Extraction System
DOI：https://doi.org/10.1016/j.ecoleng.2025.107868