Zhang et al. (2026) Fill-spill process-guided hydrologic modeling: enhanced identification of hydrologically sensitive zones and simulations in semi-arid basins

Identification

• Journal: Journal of Hydrology
• Year: 2026
• Date: 2026-02-23
• Authors: Hanchen Zhang, Xiaohan Xu, Qing Cao, Qian Li
• DOI: 10.1016/j.jhydrol.2026.135188

Research Groups

• School of Geography and Planning, Ningxia University, Yinchuan, China
• School of Hydrology and Water Resources, Nanjing University of Information Science and Technology, Nanjing, Jiangsu, China

Short Summary

This study proposes the Hydrologically Sensitive Fill-Spill Zone (HSFSZ) concept and develops the CASC2D-HSFSZ model to improve flood simulation accuracy in semi-arid regions by explicitly incorporating depression-storage and threshold-activated connectivity, demonstrating enhanced performance over the original CASC2D model.

Objective

• To propose and examine the Hydrologically Sensitive Fill-Spill Zone (HSFSZ) concept, a process-based hypothesis for runoff generation in semi-arid regions.
• To develop and apply the CASC2D-HSFSZ model to enhance flood simulation accuracy in semi-arid basins.

Study Configuration

• Spatial Scale: Huangjiahe River basin. HSFSZs were identified accounting for 13%, 30%, and 53% of the watershed area. Multi-scale grid resolution data were employed.
• Temporal Scale: Seven flood events occurring between 1981 and 2010.

Methodology and Data

• Models used: CASC2D model, CASC2D-HSFSZ model (a structural variant of CASC2D embedding an HSFSZ identification system).
• Data sources: Multi-scale grid resolution data; factors for HSFSZ identification including natural depression distribution, topographic wetness index, Euclidean distance to the nearest stream channel, and land use types.

Main Results

• The 30% HSFSZ configuration was identified as the most effective for the Huangjiahe River basin.
• Compared to the original CASC2D model, the optimized CASC2D-HSFSZ model achieved notable improvements:
  • Nash–Sutcliffe Efficiency (NSE) increased from 0.75 to 0.78.
  • Relative error in runoff depth decreased from -21.18% to -8.22%.
  • Peak flow relative error remained stable (from -36.01% to -36.58%).
• The CASC2D-HSFSZ model significantly improves flood simulation accuracy in semi-arid regions by explicitly accounting for spatial heterogeneity in hydrological processes.

Contributions

• Introduction of the Hydrologically Sensitive Fill-Spill Zone (HSFSZ) concept as a process-based hypothesis for runoff generation in semi-arid regions.
• Development of the CASC2D-HSFSZ model, integrating an HSFSZ identification system into a distributed hydrological model.
• Demonstration of enhanced flood simulation accuracy in semi-arid regions through explicit accounting of spatial heterogeneity in hydrological processes.
• Provides a scientifically robust and technically sound approach for regional water resource management and flood mitigation.

Funding

• Not specified in the provided text.

Citation

@article{Zhang2026Fillspill,
  author = {Zhang, Hanchen and Xu, Xiaohan and Cao, Qing and Li, Qian},
  title = {Fill-spill process-guided hydrologic modeling: enhanced identification of hydrologically sensitive zones and simulations in semi-arid basins},
  journal = {Journal of Hydrology},
  year = {2026},
  doi = {10.1016/j.jhydrol.2026.135188},
  url = {https://doi.org/10.1016/j.jhydrol.2026.135188}
}