Evaluating runoff retention and associated flood mitigation services of urban blue-green infrastructure in a mega urban centre

doi:10.1016/j.regsus.2026.100370

Abstract

Abstract:

Urban blue-green infrastructure (BGI) plays a significant role in regulating stormwater management and mitigating urban flooding. However, the effectiveness of urban BGI in mitigating surface runoff remains insufficiently explored, particularly in densely populated, flood-prone cities. This study presents an integrated geospatial framework to evaluate the runoff retention capacity of urban BGI and their associated flood mitigation services in Kolkata City, India. The Integrated Valuation of Ecosystem Services and Trade-Offs (InVEST)-Urban Flood Risk Mitigation (UFRM) model was applied to estimate the potential runoff generation and retention under two rainfall scenarios in Kolkata City. The model incorporated land use and land cover types, hydrological soil groups, and rainfall inputs to simulate spatial runoff patterns and runoff retention potential across different urban micro-watersheds. Flood mitigation services provided by BGI were quantified in terms of runoff retention capacity and flood volume generation. The results show that urban BGI provides substantial runoff retention capacity, with tree-covered lands and herbaceous wetlands retaining 45.00%-60.00% more runoff than impervious surfaces. Spatial analysis indicates that regions with permeable surfaces and dense vegetation cover enhance infiltration and water absorption, thereby demonstrating the hydrological effectiveness of BGI. The InVEST-UFRM results were validated with Synthetic Aperture Radar-derived flood data and machine learning-based models, including Random Forest (RF) model and eXtreme Gradient Boosting (XGBoost) model, with the area under curve scores (XGBoost model: 0.73; RF model: 0.70) confirming the model’s ability to predict flood risk. This integrated framework provides a practical tool for assessing the flood mitigation potential of BGI and offers practical insights for urban planners and policy-makers seeking to improve urban flood management and support more resilient urban landscapes.

Key words: Blue-green infrastructure (BGI), Runoff retention index, Flood mitigation services, Runoff retention capacity, Land use and land cover (LULC), Kolkata

Md Rejaul ISLAM, Mohd RIHAN, Intejar ANSARI, SHAHFAHAD , Mohd Waseem NAIKOO, Swapan TALUKDAR, Atiqur RAHMAN. Evaluating runoff retention and associated flood mitigation services of urban blue-green infrastructure in a mega urban centre[J]. Regional Sustainability, 2026, 7(4): 100370.

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No.	BGI	Location	Area (km²)	Characteristics of BGI
1	Maidan	22°33′N, 88°20′E	1.61	Tree-covered lands and grasslands
2	Fort William	22°33′N, 88°19′E	1.14	Tree-covered lands and grasslands
3	Bidhan Park	22°34′N, 88°23′E	0.26	Water body and tree-covered lands
4	Subhas Sarobar	22°33′N, 88°24′E	0.30	Water body
5	Royal Calcutta Golf Club	22°29′N, 88°21′E	0.75	Tree-covered lands and grasslands
6	Rabindra Sarovar	22°30′N, 88°21′E	0.88	Water body and tree-covered lands
7	Tollygunge Golf Club	22°29′N, 88°20′E	0.52	Tree-covered lands and grasslands
8	Nature Park	22°31′N, 88°17′E	0.50	Water body and tree-covered lands

Data type	Spatial resolution	Source	Purpose
Elevation data in the form of a DEM	30.0 m	USGS Earth Explorer portal	Elevation and watershed delineation and channel identification
LULC data	10.0 m	ESRI	Identification of LULC types
Daily rainfall data	0.5°	NASA POWER	Rainfall trends and DDF curve
Hydrologic soil group data	250.0 m	Global Hydrologic Soil Groups (HYSOGs250m)	Soil properties including texture and organic matter
BGI sites	0.5 m	Google Earth	Delineation of BGI boundaries
Flood extent data	20.0 m	Sentinel-1 SAR	Validation of the UFRM model outcome

Soil texture code	Hydrological soil group	Description	Area (km²)	Area percentage (%)	Resampled hydrological soil group
3	C	Moderately high runoff potential (<50.00% sand and 20.00%-40.00% clay)	107.23	53.68	C
4	D	High runoff potential (<50.00% sand and >40.00% clay)	31.38	15.71	D
13	C/D	Moderately high runoff potential, poorly drained (<50.00% sand and 20.00%-40.00% clay)	48.90	24.48	D
14	D/D	High runoff potential, poorly drained (<50.00% sand and >40.00% clay)	12.25	6.13	D

Runoff potential (mm)	Rainfall scenario 1		Rainfall scenario 2
Runoff potential (mm)	Area (km²)	Area percentage (%)	Area (km²)	Area percentage (%)
0.00-5.00	68.78	34.45	59.52	29.82
5.01-10.00	0.76	0.38	0.00	0.00
10.01-15.00	108.18	54.19	9.26	4.64
15.01-20.00	0.00	0.00	0.76	0.38
>20.01	21.91	10.98	130.09	65.16

LULC type	Runoff retention index		Runoff retention volume (m³)
LULC type	Rainfall scenario 1	Rainfall scenario 2	Rainfall scenario 1	Rainfall scenario 2
Grassland	0.82	0.72	24.28	29.41
Water bodies	0.98	0.98	29.64	40.82
Road	0.17	0.13	4.95	5.11
Herbaceous wetland	0.96	0.96	29.64	40.82
Bare/open land	0.60	0.50	17.80	20.24
Tree-covered land	0.84	0.75	24.97	30.43
Built-up area	0.50	0.40	14.79	16.52