Understanding the impacts of decentralized circular water strategies for combined sewer overflow and urban flooding

Meghna Rajbhandari; Fernanda Cruz Rios; Katelyn M Singh; Franco A Montalto; Ahmad Haseeb Payab; Amanda Carneiro Marques

doi:10.1016/j.uclim.2026.102887

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Understanding the impacts of decentralized circular water strategies for combined sewer overflow and urban flooding

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Understanding the impacts of decentralized circular water strategies for combined sewer overflow and urban flooding

Meghna Rajbhandari, Fernanda Cruz Rios, Katelyn M Singh, Franco A Montalto, Ahmad Haseeb Payab and Amanda Carneiro Marques

Urban Climate, v 67, 102887

Jun 2026

DOI: https://doi.org/10.1016/j.uclim.2026.102887

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Abstract

Combined sewer systems

Greywater reuse

Rainwater harvesting

Water-efficient fixtures

Circular water

Climate change

Combined sewer overflows (CSOs) and urban flooding remain critical challenges in many urban areas due to undersized, aging sewer infrastructure and increased runoff, and are projected to intensify with urbanization, population growth, and climate change. This study evaluates how decentralized, household-scale circular-water strategies influence sewer performance and assesses their potential to reduce CSO discharges and flooding under present and future climate conditions. A calibrated 1D Personal Computer Strom Water Management Model (PCSWMM) was used to simulate and evaluate 16 circular-water configurations, along with climate stress tests incorporating precipitation intensification (+10%, +20%, +30%) and Sea Level Rise (SLR) (+0.3 m, +0.9 m, +1.8 m) scenarios. Results show that combined strategies (greywater reuse, rainwater harvesting, and efficient fixtures) achieved the greatest reduction in CSO and flood volumes by 11% relative to the baseline. Under climate stress, CSO discharges increased with precipitation intensification but declined under high sea level rise due to outfall submergence, while flooding increased as elevated tidal levels restricted outfall capacity. When circular-water strategies were applied under the same climate projections, the system exhibited resilience, with combined strategies reducing CSO by 11–12% and flood volumes by 11–13% relative to each climate-stressed baseline. Although decentralized interventions alleviated hydraulic stress, projected climate extremes indicate the need for supplemental centralized infrastructure to fully manage overflow and flooding risks. Overall, findings demonstrate that these strategies can meaningfully reduce sewer pressures, enhance resilience under compound climate stressors, and support integrated adaptation planning for communities.

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Title: Understanding the impacts of decentralized circular water strategies for combined sewer overflow and urban flooding
Creators: Meghna Rajbhandari - Drexel University, Civil, Architectural, and Environmental Engineering
Fernanda Cruz Rios - Drexel University, Civil, Architectural, and Environmental Engineering
Katelyn M Singh - Drexel University, Civil, Architectural, and Environmental Engineering
Franco A Montalto - Drexel University, Civil, Architectural, and Environmental Engineering
Ahmad Haseeb Payab - Drexel University, Civil, Architectural, and Environmental Engineering
Amanda Carneiro Marques (Corresponding Author) - Drexel University, Civil, Architectural, and Environmental Engineering
Publication Details: Urban Climate, v 67, 102887
Publisher: Elsevier
Number of pages: 19
Grant note: Longsview Fellowship Program for Resources Stewardship and Sustainability - Drexel University Supporting Regional Implementation of Integrated Climate Resilience: Consortium for Climate Risks in the Urban Northeast (CCRUN) Phase III: NA21OAR4310313
This research was supported by the Longsview Fellowship Program for Resources Stewardship and Sustainability provided by Drexel University. We gratefully acknowledge partial funding from the Supporting Regional Implementation of Integrated Climate Resilience: Consortium for Climate Risks in the Urban Northeast (CCRUN) Phase III (NA21OAR4310313) as part of Integrated Project #4. We also thank Timothy Feeney, Environmental Engineer at the Camden County Municipal Utilities Authority (CCMUA) for his invaluable insights and contributions to this study.
Resource Type: Journal article
Language: English
Academic Unit: Civil, Architectural, and Environmental Engineering
Web of Science ID: WOS:001742329500001
Scopus ID: 2-s2.0-105035082018
Other Identifier: 991022172976704721