Xie et al. (2025) Assessing the impact of green infrastructure spatial distributions on hydrological connectivity and runoff reduction using landscape metrics

Identification

• Journal: Ecological Indicators
• Year: 2025
• Date: 2025-11-20
• Authors: Mengxia Xie, Ting Fong May Chui
• DOI: 10.1016/j.ecolind.2025.114417

Research Groups

• Department of Civil Engineering, The University of Hong Kong

Short Summary

This study systematically evaluates how three green infrastructure (GI) spatial strategies (uniform, random, and junction-based) affect runoff reduction, hydrological connectivity (HC), and landscape integrity in an urban watershed. It finds that spatial configuration, beyond total GI quantity, drives multifunctional performance, with trade-offs where intermediate-sized GI maximizes runoff reduction, while larger, interspersed GI patches better preserve HC.

Objective

• To systematically evaluate how distinct GI spatial strategies (uniform, random, and junction-based) influence runoff and hydrological connectivity (HC) when total GI coverage is held constant.
• To identify which configuration attributes (unit size, dispersion/interspersion, proximity to flow-accumulation zones, upstream vs. downstream placement) most strongly govern the trade-offs between runoff reduction and HC preservation.
• To assess the robustness of these relationships across heterogeneous watershed conditions (e.g., soil/permeability variations) and inform landscape integrity in urban design.

Study Configuration

• Spatial Scale: Taylor Creek watershed, Seattle, Washington, USA, covering 0.67 square kilometers.
• Temporal Scale: Two years (2009 for calibration, 2010 for validation) for simulation results, following a warm-up period from 2005 to 2008.

Methodology and Data

• Models used: VELMA 2.1 (hydrological model), FRAGSTATS v4.2 (landscape metrics), Ordinary Least Squares (OLS) regression.
• Data sources:
  • Elevation: United States Geological Survey (USGS) National Elevation Dataset (3-meter resolution).
  • Soils: United States Department of Agriculture (USDA) State Soil Geographic Database.
  • Land cover: Seattle GeoData (Building Outline & Road, Tree Canopy), Multi-Resolution Land Characteristics (MRLC) Consortium (30-meter resolution), EPA (10-meter resolution).
  • Daily weather data: National Oceanic and Atmospheric Association (NOAA) stations (Sand Point and Boeing Field).
  • Daily runoff: King County Discharge (Seattle Public Utilities site SPU_STA401).

Main Results

• Increasing green infrastructure (GI) coverage consistently reduces runoff but weakens hydrological connectivity (HC) (p<0.001).
• Junction-based GI distributions at flow-accumulation points achieved the largest runoff reductions but resulted in lower HC compared to random or uniform distributions.
• Runoff reduction is maximized by intermediate-sized GI units (41.7 m²), while HC is better preserved by larger (207.8 m²), internally continuous patches placed across multiple locations.
• More interspersed GI layouts (random and uniform) better preserve HC, albeit with a modest loss of interception efficiency compared to junction-based distributions.
• The proportion of subsurface HC increased across all GI scenarios relative to the base scenario (mean Δlogit = 0.0825, p<0.001), indicating a robust shift towards enhanced subsurface connectivity.
• OLS regression showed that greater GI coverage and more irregular GI shapes enhanced runoff reduction, while larger individual GI units and excessive interspersion weakened performance. For HC, greater GI coverage was negatively associated, but more interspersed GI patches were positively associated.
• Sensitivity analysis confirmed that the direction and relative ordering of GI effects on runoff and HC remained consistent despite parametric perturbations, with GI stabilizing HC variability.

Contributions

• Elevates hydrological connectivity (HC) from a by-product to a primary performance target in GI evaluation.
• Disentangles the roles of GI quantity versus spatial configuration in shaping multifunctional hydrological and ecological outcomes.
• Provides configuration-explicit guidance for GI planning that supports urban flood resilience and ecohydrological restoration, moving beyond runoff-centric design to connectivity-aware planning.
• Introduces a novel spatial evaluation framework that jointly considers hydrological, ecological, and spatial metrics, offering a nuanced analysis transferable across planning contexts.

Funding

• Research Grants Council, University Grants Committee (HK) (Project No. HKU17204023).

Citation

@article{Xie2025Assessing,
  author = {Xie, Mengxia and Chui, Ting Fong May},
  title = {Assessing the impact of green infrastructure spatial distributions on hydrological connectivity and runoff reduction using landscape metrics},
  journal = {Ecological Indicators},
  year = {2025},
  doi = {10.1016/j.ecolind.2025.114417},
  url = {https://doi.org/10.1016/j.ecolind.2025.114417}
}