Green roof research towards enhancing urban biodiversity, storm-water retention and air pollution abatement

Green roofs provide multiple environmental benefits. These include storm-water retention, water purification, insulation of the building, air quality and carbon sequestration and biodiversity enhancement. Green roofs can be classified as sustainable extensive green roofs (no additional fertilizer, no gardening, no irrigation and shallow growing substrate) or as intensive green roofs (additional fertilizer, gardening, irrigation and deeper growing substrate). In this review, we concentrate on multi-disciplinary benefits of green roofs - i.e. biodiversity enhancement (i.e. reconciliation ecology), storm-water retention and air-pollution abatement as these benefits highly support sustainable buildings. We have found that under conditions of very fine-scale heterogeneity, species diversity (both plants and arthropods) is unlikely to increase, particularly if there is no irrigation. Under large-scale heterogeneity (such as different types of green roofs), the regional diversity can increase. Some plants compete with each other and others can create facilitation. Under conditions of irrigation in the hot, arid conditions of the Middle East, photovoltaic panels may likely produce more electricity and the heterogeneity in solar radiation and moisture can result in greater biodiversity. Rainwater can also be deterred from storm drainage by using gray water irrigation for specific plant assemblages. Green roofs can help mitigate the negative effects of air pollution and CO₂ emissions - in particular, by absorbing pollutants and sequestering carbon dioxide.