Using a Hydrological Model to Simulate the Performance and Estimate the Runoff Coefficient of Green Roofs in Semiarid Climates

Josefina Herrera,Sergio Vera,Francisco Suárez,Gilles Flamant,Jorge Gironás,Waldo Bustamante,Carlos Bonilla

doi:10.3390/w10020198

Abstract

Green roofs offer a series of benefits to buildings and to the urban environment. Their use in dry climates requires optimizing the choice of their components (i.e., vegetation, substrate and drainage layer) for the specific local climatic conditions, in order to minimize irrigations needs while preserving the attributes of the roof. In this study, we calibrated and validated an existing hydrological model—IHMORS—for the simulation of the hydrological performance of green roofs. Simulated results were compared to experimental data obtained in an outdoor test facility on several green roof specimens, representing a variety of green roofs configurations. IHMORS was able to reasonably predict the soil moisture dynamics for all tested specimens. The specimens of 10 cm depth were the best simulated by the model, while some overestimation was observed during the model validation for the 5 and 20 cm depth specimens. The model was then used to estimate the number of days in which irrigation is needed, as well as analyze the water runoff control performance of all specimens. We related the amount of water retained by the substrate and depth, magnitude and intensity of precipitation event, and the initial substrate moisture. For all events, the lowest runoff coefficient was simulated for the 20 cm specimens. Our study showed the full potential of the model for estimating the water needs and the runoff control performances of different variants of green roofs.

Highlights

Green roofs are a type of green infrastructure technology that has been incorporated into the design and construction of buildings because of the benefits they offer to the buildings themselves and to the urban environment
The parameter S was calibrated by minimizing the error between the and the simulated data of the volumetric water content (VWC) of the substrate of each green roof specimen
This study showed the full potential of the hydrologic model IHMORS to correctly evaluate the hydrological behavior of a wide variety of green roofs and estimate the potential irrigation needs and runoff control performance

Summary

Introduction

Green roofs are a type of green infrastructure technology that has been incorporated into the design and construction of buildings because of the benefits they offer to the buildings themselves and to the urban environment. These systems preserve and recreate the natural landscape features to treat storm water as a resource rather than a waste [3]. They are able to infiltrate precipitation and collect runoff from impervious surfaces, with the retained volume being redistributed to other layers and/or eventually evapotranspired. The simulation of (1) surface/subsurface processes and (2) the continuous dynamics of the soil water content controlled by evapotranspiration and irrigation are essential to study the performance of green infrastructure and evaluate plant survival and the overall sustainability of drainage techniques in arid and semiarid regions [11,12]

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