Rainwater-irrigated greenroofs as climate change adaptation in urban areas

Urban greening plays an important role as a tool for climate change mitigation, adaptation and environmental protection. An extensive green roof is one the most favorite methods of urban greening as it does not require additional area and intensive maintenance and is also efficient as a rain water retention during extreme events and for the deposition of particulate matter. However, it is not very efficient for cooling at pedestrian level, for CO₂ sequestration and biodiversity. The suggested solution is to convert the extensive green roofs into semi-intensive using automatic solar-powered irrigation system with collected rainwater. The model green roof was built and experiment was carried out starting in 2020. The roof was irrigated during the summer months with 2 mm day^-1. The green roof effects on microclimate, WBGT index, water balance, particulate matter binding, greenhouse gas fluxes and biodiversity are measured continuously and compared to a reference area of a parking lot. In addition albedo and surface temperature measurements were carried out using manual instruments and different drone-borne thermal cameras. The results show higher albedo of irrigated roof than parking lot. The microclimatic effects of semi-intensive roof on the microclimate are quite variable. The surface temperatures differences within the roof are more extreme than on the parking lot. However, the air temperature extremes are lower. The air temperature reduction comparing to parking lot is more pronounced during the night time and under calm conditions, with minimal external influences. During the daytime the warming effects of the roof are well-expressed depending on the weather conditions. The effects of different plant species and substrate to total cooling or warming of green roof were also quantified.