Zhou et al. (2025) Contrasting runoff response times regulated by vegetation and climate changes in typical dry and wet basins

Identification

• Journal: Journal of Hydrology Regional Studies
• Year: 2025
• Date: 2025-12-15
• Authors: Xuan Zhou, Baolin Xue, Guoqiang Wang, Qingqing Fang, Jingfeng Xiao, Yuntao Wang, Yinglan A, Jin Wu, Mimi Gong
• DOI: 10.1016/j.ejrh.2025.103044

Research Groups

• Advanced Interdisciplinary Institute of Satellite Applications, Beijing Normal University, Beijing, China
• School of Water Resources and Hydropower Engineering, North China Electric Power University, Beijing, China
• Earth Systems Research Center, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, USA

Short Summary

This study investigated how runoff timing, particularly flood timing, has changed over four decades in three Chinese river basins under the combined influence of climate change and large-scale afforestation, finding that afforestation delays flood timing more in semi-arid regions, while humid regions are more influenced by precipitation changes.

Objective

• To characterize the changes in runoff response times across three representative Chinese basins over the past decades.
• To investigate the nonlinear relationships between runoff responses and environmental changes using Generalized Additive Models (GAMs).
• To quantify the relative contributions of climate change and afforestation to variations in runoff response time.

Study Configuration

• Spatial Scale: Three river basins in China: Hailar River Basin (HRB) in northeastern China (6.2 × 10^4 km^2, semi-arid), Xijiang River Basin (XRB) in southern China (1.32 × 10^5 km^2, humid karst), and Dongjiang River Basin (DRB) in southeastern China (2.6 × 10^4 km^2, humid).
• Temporal Scale: Four decades, with specific data ranges: daily streamflow (long-term, including 1970-1975 and 2010-2015 for comparison), forest area (1982-2015), NDVI (1982-2019), and meteorological data (1982-2019 for GAM analysis). Analysis periods were divided before and after major afforestation projects (HRB: 2000; XRB/DRB: 1996).

Methodology and Data

• Models used:
  • Circular statistics (for Center Timing, Flood Timing, Spring Flood Timing indices)
  • Adjusted Theil–Sen slope estimator (for trend analysis)
  • Wavelet analysis (for periodic components)
  • Mann–Kendall (M-K) statistical analysis (for monotonic trends and significance)
  • Generalized Additive Models (GAMs) (for nonlinear relationships and attribution of factors)
• Data sources:
  • Daily streamflow: Hydrological Year Books, Ministry of Water Resources of the People’s Republic of China.
  • Meteorological data (precipitation, air temperature, relative humidity): China Meteorological Administration stations.
  • Snow depth (SD), Soil Water Content (SWC): ECMWF Reanalysis v5 (ERA5) dataset (hourly level-1, converted to annual scale).
  • Forest area: Remote-sensing land-cover product (Liu et al., 2020) (annual updates, 1982-2015, 5 km spatial resolution).
  • Normalized Difference Vegetation Index (NDVI): PKU GIMMS NDVI3g (1982–2019, 0.083° spatial resolution).

Main Results

• Runoff coefficients decreased in all three basins from the pre-afforestation period (1970-1975) to the post-afforestation period (2010-2015): HRB (-0.04), XRB (-0.017), and DRB (-0.011).
• All three basins showed a persistent greening trend, with significant increases in forest cover and NDVI over the three decades (e.g., XRB: >60.61% of basin area showed significant NDVI increase).
• Runoff timing, particularly flood timing (FT), has shifted significantly under the combined influence of climate variability and forest expansion, with FT changes being more pronounced than shifts in mean runoff timing (CT).
• Afforestation substantially delayed flood peaks in the semi-arid Hailar River Basin (HRB), contributing 64.94% to FT delay.
• In the humid Xijiang River Basin (XRB) and Dongjiang River Basin (DRB), the effect of forest expansion on flood timing was weaker; earlier and more concentrated precipitation could advance floods, overriding afforestation effects.
• Precipitation regime (total precipitation and precipitation intensity) and antecedent soil moisture emerged as primary controls on center timing (CT) and spring flood timing (SFT).
• Temperature and vegetation (forest area and NDVI) primarily modulated flood peaks (FT).
• In the karst XRB, afforestation had no significant effect on FT, attributed to its unique hydrogeological setting with high permeability and complex surface-groundwater interactions.

Contributions

• Provided a systematic assessment of the joint and timing-specific effects of climate change and afforestation on runoff response time, addressing a critical research gap.
• Developed and applied a robust methodological framework using Generalized Additive Models (GAMs) to characterize multiple runoff timing responses (CT, FT, SFT) and quantify their nonlinear dependencies on environmental drivers.
• Offered new hydrological insights by contrasting runoff response times in typical dry and wet basins, highlighting that afforestation policies must be tailored to local hydroclimatic contexts.
• Demonstrated that afforestation in water-scarce basins requires cautious implementation to balance flood mitigation benefits against potential reductions in water availability.

Funding

• National Science Fund for Distinguished Young Scholars (No. 52125901)
• National Natural Science Foundation of China (No. 52379002)

Citation

@article{Zhou2025Contrasting,
  author = {Zhou, Xuan and Xue, Baolin and Wang, Guoqiang and Fang, Qingqing and Xiao, Jingfeng and Wang, Yuntao and A, Yinglan and Wu, Jin and Gong, Mimi},
  title = {Contrasting runoff response times regulated by vegetation and climate changes in typical dry and wet basins},
  journal = {Journal of Hydrology Regional Studies},
  year = {2025},
  doi = {10.1016/j.ejrh.2025.103044},
  url = {https://doi.org/10.1016/j.ejrh.2025.103044}
}