Abstract

Urbanization and climate change have increased the frequency and intensity of urban flooding, particularly in tropical cities such as those in Malaysia. Green roofs offer a promising low-impact development (LID) strategy for stormwater management by reducing runoff volume and peak discharge; however, there remains limited understanding of how roof slope influences green roof hydrological performance under tropical rainfall conditions. This study evaluates the effectiveness of green roofs with different slopes in reducing peak runoff and assesses the capability of the EPA Storm Water Management Model (SWMM) to simulate slope-dependent runoff responses. Experimental runoff data were obtained from a laboratory-scale green roof model with slopes of 2% and 6%, subjected to controlled simulated rainfall events, and were used for calibration and validation of EPA SWMM, focusing on key indicators including peak discharge and time to peak. Results show that green roofs significantly reduced peak discharge compared to conventional roofs, with reductions of 97.2% at 2% slope and 95.4% at 6% slope, with the shallower slope exhibiting greater runoff attenuation associated with delayed runoff response. SWMM simulations demonstrated satisfactory agreement with observed data, with Nash–Sutcliffe Efficiency (NSE) values between 0.50 and 0.65 and RMSE–observations standard deviation ratio (RSR) values between 0.58 and 0.68. Overall, the findings indicate that green roofs, including those on steeper slopes, are effective in attenuating stormwater runoff, and that EPA SWMM is a suitable tool for comparative modelling of green roof hydrology under tropical conditions. These insights support the integration of green roofs into urban stormwater planning in Malaysia and similar environments.

Keywords

References

1. Asman, N. S. A., Dullah, S., Amaludin, A. E., Matlan, S. J., Ayog, J. L. & Baharum, A. 2019. The hydrological performance investigation of green roof. Journal of Advanced Research in Engineering Knowledge, 9(1), 14-25.
2. Asman, N. S. A., Dullah, S., Mirasa, A. K., Ayog, J. L. & Djamila, H. 2017. Water runoff quality of green roof using natural fibres and recycle waste material. Transactions on Science and Technology, 4(2), 143-148.
3. Berndtsson, J. C. 2010. Green roof performance towards management of runoff water quantity and quality: A review. Ecological Engineering, 36, 351-360.
4. Burns, M. J., Fletcher, T. D., Walsh, C. J., Ladson, A. R. & Hatt, B. E. 2012. Hydrologic shortcomings of conventional urban stormwater management and opportunities for reform. Landscape and Urban Planning, 105, 230-240.
5. Chow, M. F., Abu Bakar, M. F. & Mohd Razali, M. H. 2018. Effects of slopes on the stormwater attenuation performance in extensive green roof. IOP Conference Series: Earth and Environmental Science, 164, 012029.
6. Ferreira, M. J. & da Rocha, H. R. 2023. Green roof infrastructure outperforms grey technology in flood mitigation in São Paulo’s urbanized region. Frontiers in Built Environment, 9, 1254942.
7. Getter, K. L. & Rowe, D. B. 2006. The role of extensive green roofs in sustainable development. HortScience, 41(5), 1276-1285.
8. Hamid, H. N. A., Romali, N. S. & Rahman, R. A. 2023. Key barriers and feasibility of implementing green roofs on buildings in Malaysia. Buildings, 13(9), 2233.
9. Jamei, E., Chau, H. W., Seyedmahmoudian, M., Mekhilef, S. & Hafez, F. S. 2023. Green roof and energy – role of climate and design elements in hot and temperate climates. Heliyon, 9(5), e15917.
10. Kaewpraek, C., Ali, L., Rahman, M. A., Shakeri, M., Chowdhury, M. S., Jamal, M. S., Mia, M. S., Pasupuleti, J., Dong, L. K. & Techato, K. 2021. The Effect of Plants on the Energy Output of Green Roof Photovoltaic Systems in Tropical Climates. Sustainability, 13(8), 4505.
11. Landon, M. E., Mitchell, C. E., Taguchi, V. J. & Hunt, W. F. 2025. Assessing the water quality impact of floating treatment wetlands strategically placed in two stormwater retention ponds. Journal of Environmental Management, 374, 124084.
12. Mendes, A. M., Monteiro, C. M. & Santos, C. 2025. Green Roofs Hydrological Performance and Contribution to Urban Stormwater Management. Water Resources Management, 39, 1015-1031.
13. Mentens, J., Raes, D. & Hermy, M. 2006. Green roofs as a tool for solving the rainwater runoff problem in the urbanized 21st century? Landscape and Urban Planning, 77, 217-226.
14. Mohamed, M. A., Zaman, A. Q. M., Kajewski, S. & Trigunarsyah, B. 2024. Enhancing flood disaster management in Klang Valley. Jurnal Kejuruteraan, 36(6), 2709-2715.
15. Moriasi, D. N., Arnold, J. G., Van Liew, M. W., Bingner, R. L., Harmel, R. D. & Veith, T. L. 2007. Model evaluation guidelines for systematic quantification of accuracy in watershed simulations. Transactions of the ASABE, 50(3), 885-900.
16. Patel, P., Karmakar, S., Ghosh, S., Aliaga, D. G. & Niyogi, D. 2021. Impact of green roofs on heavy rainfall in tropical, coastal urban area. Environmental Research Letters, 16, 074051.
17. Pragati, S., Priya, R. S., Pradeepa, C. & Senthil, R. 2023. Simulation of the Energy Performance of a Building with Green Roofs and Green Walls in a Tropical Climate. Sustainability, 15(3), 2006.
18. Qin, Y. 2020. Urban Flooding Mitigation Techniques: A Systematic Review and Future Studies. Water, 12(12), 3579.
19. Rossman, L. A. 2010. Storm Water Management Model User’s Manual, Version 5.0. Cincinati: U. S. Environmental Protection Agency.
20. Shamsuri, N., Bakar, R. A. & Unjah, T. 2018. Flash flood impact in Kuala Lumpur – Approach review and way forward. International Journal of the Malay World and Civilisation, 6(Special Issue 1), 69-76.
21. Shuster, W. D., Bonta, J., Thurston, H., Warnemuende, E. & Smith, D. R. 2005. Impacts of impervious surface on watershed hydrology: A review. Urban Water Journal, 2(4), 263-275.
22. Stovin, V., Vesuviano, G. & Kasmin, H. 2012. The hydrological performance of a green roof test bed under UK climatic conditions. Journal of Hydrology, 414-415, 148-161.
23. Weggemans, J., Santos, M. L., Ferreira, F., Moreno, G. D. & Matos, J. S. 2023. Modeling the hydraulic performance of pilot green roofs using the Storm Water Management Model: How important is calibration? Sustainability, 15(19), 14421.
24. Wong, G. K. L. & Jim, C. Y. 2014. Quantitative hydrologic performance of extensive green roof under humid-tropical rainfall regime. Ecological Engineering, 70, 366-378.