Experimental comparison of two extensive green roof designs in Northwest Mexico

Abstract

Accelerated population growth and urbanization have negative environmental impacts, such as habitat destruction, biodiversity loss, natural resource depletion, and pollution. They speed up climate change, contribute to urban heat islands, and increase energy use. Green roofs (GRs) can reduce the ecological footprint and improve the quality of life within cities but require careful design for best results. This study analyzes the thermal performance of GRs in six experimental modules differing in roof cover: concrete, reflective coating, dry soil, wet soil, traditional GR with Sedum acre, and wetland GR with Salicornia pacifica. The two plant species have different carbon assimilation metabolisms: S. pacifica is a native wetland C3 species with diurnal transpiration that grows in flooded soils, and S. acre is an exotic Crassulacean Acid Metabolism (CAM) species with night-time transpiration, commonly used in GRs. GRs were monitored during the winter of 2020 in Ensenada, Baja California, México, a city with a semi-arid Mediterranean climate. We found that vegetated covers reduced the temperature oscillation with an insulating effect. During the warmest week, they reduced the internal roof surface temperature (Ts,in) up to 12.4 °C in comparison to the concrete roof. They maintained Ts,in up to 5.8 °C warmer than concrete roof during the coldest week, indicating that GRs are efficient thermal regulators in this region, potentially reducing buildings’ thermal load as well as providing additional ecosystemic services. Since S. pacifica had higher survival and coverage, we recommend its use in GRs located in Northwest Mexico and climatically similar world regions.