Zhou et al. (2026) Effects of the competing controlling factors of rainfall, landscape position and soil depth on moisture responses in the Mollisol region of China

Identification

• Journal: Agricultural Water Management
• Year: 2026
• Date: 2026-03-31
• Authors: Tong Zhou, Yanru Wen, Litao Lin, Bao Liu, Yueling Zhang, Yaji Wang, Wenbin Wu
• DOI: 10.1016/j.agwat.2026.110325

Research Groups

• State Key Laboratory of Efficient Utilization of Arable Land in China, Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing, China
• Department of Environment - Soil-Environment Systems Exploration and Engineering Group, Ghent University, Gent, Belgium
• Chinese Research Academy of Environmental Sciences, Beijing, China
• State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, China

Short Summary

This study quantified the interactive influence of rainfall patterns and landscape positions on event-scale soil moisture response metrics across various soil depths in the Mollisol region of China. It found that while midslope and downslope positions were critical for explaining response variance, rainfall type was the primary factor driving soil moisture dynamics across all depths, with heavy rainfall leading to greater and faster responses in shallow layers.

Objective

• To evaluate whether downslope (DS) profiles exhibit greater soil moisture response metrics (magnitude, time, and velocity) compared to upslope (US) and midslope (MS) positions on long, gentle hillslopes.
• To quantify the impacts of different rainfall types (light, moderate, heavy) on vertical soil moisture dynamics within the soil profile.
• To identify the main factors controlling soil moisture responses across diverse rainfall regimes, landscape positions, and soil depths.

Study Configuration

• Spatial Scale: Two hillslopes (S1 and S2), each over 1000 meters long, within a 1.45 x 10⁶ square meter agricultural catchment in Hongxing Farm, Bei'an County, Heilongjiang Province, Northeast China (Mollisol region). Soil moisture was monitored at three landscape positions (upslope, midslope, downslope) and five depths (0.1, 0.2, 0.3, 0.6, and 1.0 meters).
• Temporal Scale: Rainfall season of 2023 (May to September), encompassing 52 distinct rainfall events. Soil moisture was recorded hourly.

Methodology and Data

• Models used: Not applicable (observational study with statistical analysis). Statistical methods included two-way and three-way Analysis of Variance (ANOVA), Tukey’s Honestly Significant Difference (HSD) multiple comparisons, and Spearman’s correlation analysis.
• Data sources:
  • Soil moisture: Frequency Domain Reflectometry (FDR) sensors (Insentek) installed at specified depths.
  • Rainfall: Daily rainfall data from a standard rain gauge station of the National Weather Service of China, approximately 3 kilometers from the study catchment.
  • Soil properties: Laboratory analysis of soil samples for bulk density and texture.

Main Results

• The soil moisture response magnitude (Δs) generally decreased with increasing soil depth and decreasing slope position, while exhibiting a positive correlation with rainfall amount.
• The response percentage of soil moisture peaked during heavy rainfall events within shallow layers (0–0.2 meters), reaching 100%, but remained limited to approximately 14% under light and moderate rainfall events in deeper layers.
• Simultaneous moisture peaks across soil layers, or earlier peaks in deeper layers during heavy rainfall events, were observed at all landscape positions.
• For hillslopes with lower initial moisture (S1), response metrics at upslope and midslope positions were slightly greater than those of hillslope S2. However, no significant differences were observed at the downslope position between S1 and S2, suggesting the influence of slope length.
• Midslope and downslope positions were critical for explaining the variance in soil moisture response, while the type of rainfall event (light, moderate, heavy) was identified as the key factor influencing moisture dynamics across all soil depths.
• Response magnitudes (Δs) varied between 0.01 and 18.53 m³ m⁻³.
• Response times (T) ranged from -3.6 x 10³ to 5.04 x 10⁴ seconds.
• Response velocities (V) ranged from 1.25 x 10⁻⁵ to 1.67 x 10⁻⁴ meters per second.
• Heavy rainfall events resulted in shorter response times and higher response velocities within the soil profile compared to light and moderate rainfall.

Contributions

• This study provides a comprehensive, spatially, and vertically intensive characterization of soil moisture responses to rainfall on long hillslopes (over 1000 meters), addressing a research gap where most previous studies focused on shorter slopes (less than 200 meters).
• It quantifies the competing effects of rainfall type, landscape position, and soil depth on soil moisture dynamics, offering a nuanced understanding of infiltration, runoff generation, and soil erosion processes in agricultural landscapes.
• The findings highlight the importance of considering response timing and regimes of peak moisture across diverse soil layers for effective erosion risk management and inform the development of more refined process-based hydrological models.
• It demonstrates that the relative importance of climatic and landscape drivers shifts with soil depth and rainfall type, emphasizing the need for detailed observations to fully characterize surface and subsurface hydrological heterogeneity.

Funding

• National Key Research and Development Programme of China (No. 2024YFD1501200)
• National Natural Science Foundation of China (No. 42407492, 42571330)
• Central Public-interest Scientific Institution Basal Research Fund (No. Y2026QC23)
• China Scholarship Council (CSC)

Citation

@article{Zhou2026Effects,
  author = {Zhou, Tong and Wen, Yanru and Lin, Litao and Liu, Bao and Zhang, Yueling and Wang, Yaji and Wu, Wenbin},
  title = {Effects of the competing controlling factors of rainfall, landscape position and soil depth on moisture responses in the Mollisol region of China},
  journal = {Agricultural Water Management},
  year = {2026},
  doi = {10.1016/j.agwat.2026.110325},
  url = {https://doi.org/10.1016/j.agwat.2026.110325}
}