Urban micro-watersheds with steep slopes and poorly draining soils generate excessive runoff and pollutant loads, posing significant management challenges. This study introduces a novel focus on a contributing zone within a 30-ha micro-watershed in Addis Ababa to assess how climate change, urbanization and their combined effects influence stormwater runoff and water quality. The Personal Computer Stormwater Management Model (PCSWMM) was employed to simulate four scenarios: baseline, climate change, urbanization, and combined impacts. The baseline model was calibrated and validated with observed storm data using the Sensitivity-Based Radio Tuning Calibration (SRTC) tool, achieving Nash–Sutcliffe Efficiency (NSE), Root Mean Square Error (RMSE)-standard deviation ratio (RSR), and Integral Square Error (ISE) values within accepted thresholds. Over a 3-h, 6,870 m3 storm, 72% became surface runoff, 18.2% infiltrated, 2% evaporated, and 6.4% remained in storage, producing a peak flow of 3.6 m3/s and localized node flooding. The climate change scenario employed an ensemble of Global Circulation Models (GCMs)—five for precipitation and seven for temperature—selected from twelve and sixteen models, respectively, based on their statistical performance. Under shared socio-economic pathway (SSP)2–4.5, 2-year return period peak flows increased to 3.8 m3/s (2024–2053) and 4.7 m3/s (2054–2083); under SSP5-8.5, they rose to 5.8 m3/s and 6.6 m3/s, respectively. An 80% imperviousness urbanization scenario increased peak flow to 4.1 m3/s. The combined scenario yielded a peak of 7.2 m3/s and a 10.3% pollutant load increase, which were (1.7%: climate change, and 7.1%: urbanization alone), highlighting urbanization as the principal driver of water quality decline. These findings highlight the need for integrated green–grey infrastructure (IGGI) and upgraded drainage systems to strengthen urban resilience. The study supports data-driven planning and advances sustainable development goals (SDGs) 6 (clean water and sanitation), 11 (sustainable cities and communities), and 13 (climate action). Graphical Abstract The graphical abstract presents a PCSWMM-based hydrologic modeling study that examines the impacts of climate change and urbanization on stormwater runoff and pollutant loads in a steeply sloped, poorly drained soil at the contributing zone of an urban micro-watershed in Addis Ababa. The first section, Urban watershed inputs, illustrates the study area and integrates key datasets, including land use, topography, soil characteristics, hydro-climatic conditions (both historical and projected), and pollutant sources. The second section, Scenario framework, outlines four modeled simulations: baseline, climate change (SSP2-4.5 and SSP5-8.5), urbanization (80% imperviousness), and a combined scenario, each feeding into the hydrologic model. The central panel, PCSWMM modeling & calibration, highlights the modeling process, including SRTC-based calibration and performance evaluation using key metrics such as NSE, RSR, and ISE. The Scenario outcomes section depicts peak flow increases of up to 100% and pollutant load rises of up to 10.3%, with urbanization alone contributing 7.1%. The final section, Urban resilience implications, underscores the necessity of integrated green–grey infrastructure (IGGI) and enhanced drainage systems to mitigate future risks and advance sustainable development goals: SDG 6 (clean water and sanitation), SDG 11 (sustainable cities and communities), and SDG 13 (climate action). The graphical abstract conveys complex hydrologic modeling insights through an accessible visual narrative tailored for urban planners, engineers, and decision-makers.

Stormwater Modeling in a Steep, Poorly Drained Contributing Micro-Watershed Zone of Addis Ababa

期刊论文
发表日期：

2025年9月9日

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Bilal Kemal,
Dereje Hailu,
Daneal Fekersillassie,
Solomon Seyoum,
Geremew Sahilu,
Aqil Tariq

摘要

Urban micro-watersheds with steep slopes and poorly draining soils generate excessive runoff and pollutant loads, posing significant management challenges. This study introduces a novel focus on a contributing zone within a 30-ha micro-watershed in Addis Ababa to assess how climate change, urbanization and their combined effects influence stormwater runoff and water quality. The Personal Computer Stormwater Management Model (PCSWMM) was employed to simulate four scenarios: baseline, climate change, urbanization, and combined impacts. The baseline model was calibrated and validated with observed storm data using the Sensitivity-Based Radio Tuning Calibration (SRTC) tool, achieving Nash–Sutcliffe Efficiency (NSE), Root Mean Square Error (RMSE)-standard deviation ratio (RSR), and Integral Square Error (ISE) values within accepted thresholds. Over a 3-h, 6,870 m³ storm, 72% became surface runoff, 18.2% infiltrated, 2% evaporated, and 6.4% remained in storage, producing a peak flow of 3.6 m³/s and localized node flooding. The climate change scenario employed an ensemble of Global Circulation Models (GCMs)—five for precipitation and seven for temperature—selected from twelve and sixteen models, respectively, based on their statistical performance. Under shared socio-economic pathway (SSP)2–4.5, 2-year return period peak flows increased to 3.8 m³/s (2024–2053) and 4.7 m³/s (2054–2083); under SSP5-8.5, they rose to 5.8 m³/s and 6.6 m³/s, respectively. An 80% imperviousness urbanization scenario increased peak flow to 4.1 m³/s. The combined scenario yielded a peak of 7.2 m³/s and a 10.3% pollutant load increase, which were (1.7%: climate change, and 7.1%: urbanization alone), highlighting urbanization as the principal driver of water quality decline. These findings highlight the need for integrated green–grey infrastructure (IGGI) and upgraded drainage systems to strengthen urban resilience. The study supports data-driven planning and advances sustainable development goals (SDGs) 6 (clean water and sanitation), 11 (sustainable cities and communities), and 13 (climate action).

Graphical Abstract

The graphical abstract presents a PCSWMM-based hydrologic modeling study that examines the impacts of climate change and urbanization on stormwater runoff and pollutant loads in a steeply sloped, poorly drained soil at the contributing zone of an urban micro-watershed in Addis Ababa. The first section, Urban watershed inputs, illustrates the study area and integrates key datasets, including land use, topography, soil characteristics, hydro-climatic conditions (both historical and projected), and pollutant sources. The second section, Scenario framework, outlines four modeled simulations: baseline, climate change (SSP2-4.5 and SSP5-8.5), urbanization (80% imperviousness), and a combined scenario, each feeding into the hydrologic model. The central panel, PCSWMM modeling & calibration, highlights the modeling process, including SRTC-based calibration and performance evaluation using key metrics such as NSE, RSR, and ISE. The Scenario outcomes section depicts peak flow increases of up to 100% and pollutant load rises of up to 10.3%, with urbanization alone contributing 7.1%. The final section, Urban resilience implications, underscores the necessity of integrated green–grey infrastructure (IGGI) and enhanced drainage systems to mitigate future risks and advance sustainable development goals: SDG 6 (clean water and sanitation), SDG 11 (sustainable cities and communities), and SDG 13 (climate action). The graphical abstract conveys complex hydrologic modeling insights through an accessible visual narrative tailored for urban planners, engineers, and decision-makers.