The maintenance of prefabricated green roofs for preserving cooling performance: A field measurement in the subtropical city of Hangzhou, China

Abstract Urban temperature increase is a critical problem for many cities. Green roofing is an approach to mitigating urban temperature increase, while the maintenance of the green roof for stable cooling potential has been less studied. Therefore, this study aims to investigate the cooling performance of prefabricated green roof for maintenance purposes. Focusing on the cooling and humidifying performance of the green roof, this study is to understand the influence of (i) vegetation species, (ii) weather condition and (iii) watering. This study was experimentally performed in the subtropical city of Hangzhou, China in the summer season, with three local vegetation species including Pomegranate, Bermuda grass and Sedum lineare. Results indicate that under sunny conditions, the Pomegranate roof was favourable with the best diurnal cooling and humidifying effects, the Bermuda grass roof could be acceptable while the Sedum lineare roof is not suggested. In comparison, all green roofs could maintain diurnal cooling and humidifying effects under cloudy conditions. Watering is critical to green roof cooling and humidifying effects. Without watering, all green roofs could elevate air temperature and dry surrounding environment and could die. The Pomegranate should be watered before 15:00 under sunny condition, while both Bermuda grass and Sedum lineare roofs should be watered before noon. Moreover, nocturnal watering makes slight differences to green roof cooling and humidifying effects. Overall, this study helps understand the green roof cooling and humidifying effects and it can instruct green roof management and maintenance.