Evidence of the Climate Mitigation Effect of Green Roofs—A 20-Year Weather Study on an Extensive Green Roof (EGR) in Northeast Germany

Abstract

Approximately 10 km2 of new green roofs are built in Germany every year. About 85% of these are Extensive Green Roofs (EGR). An EGR with several research features was installed on new buildings belonging to the University of Applied Sciences Neubrandenburg in 1999. The results of the almost 20-year permanent survey of the climate effects of the green roof in contrast to gravel roofs are presented here. High-quality sensors, similar to those used by official weather stations, are in use, and data is collected every 10 s and aggregated to hourly values which enable comparisons to official measurements made by the DWD in Neubrandenburg and Berlin. The results show the typical urban heat island effect (UHI) and the mitigation effect of EGR. Whilst the temperature increased over the years due to the urban heat island effect, the temperature within the growing media in the green roof remained constant. The EGR has a stabilization effect of 1.5 K. This is good news for all those seeking a UHI mitigation solution for city centers. In a best-case scenario, the green roof potential of cities in Germany is between 3 and 8%. A value of 50% can be achieved for all buildings; roofs represent about ¼ of urban surfaces, and the cooling effect of 1.5 K in 20 years is a reasonable contribution to cooling cities and achieving environmental goals by greening urban surfaces.

Green Roof Enhancement on Buildings of the University of Applied Sciences in Neubrandenburg (Germany) in Times of Climate Change

“…Preliminary reports presented the results of the continuous 20-year climate measurements on these roofs. The evidence of the positive influence of the microclimate of the vegetation layer is seen in a significant reduction in the surface temperature [22]. A further paper explains how different retention layers can capture larger volumes of rain in a comparison between conventional growing media and various retention layers.…”

Green Roofs and Greenpass

“…For instance, Peng and Jim [27] and Zhang et al [28] published their work regarding effects of green roofs on the thermal comfort at the pedestrian level. Both papers found a reduction of air temperature at the pedestrian level of around 0.1 to 0.3 • C. Köhler and Kaiser [29] present evidence that green roofs contribute to mitigation of climate change. But other authors did not find relevant effects on thermal comfort [30,31].…”

“…Zhang et al [28] found a reduction of air temperature at the pedestrian level of 0.1 to 0.3 • C. Both support and approve the findings of the presented paper. Ng et al [29] as well as Rosenzweig [31] in contrast concluded that green roofs have only a neglectable influence on the thermal comfort at the pedestrian level. One has to bear in mind that they derived their findings from simulations performed for areas dominated by high rise buildings, compared to Elief Playhouse.…”

“…Recently, a long-term investigation of an extensive green roof has been published that shows a minor but clear impact on the microclimate [41]. Some authors conclude that there are only minor effects on the thermal comfort of pedestrians [29,31], while others present relevant improvements [27,28,42].…”

Análisis experimental térmico entre jardines verticales y otros materiales empleados para construcción en Bogotá

“…Ahora bien, en la figura 11 se destaca un diferencial mucho más notorio que en los demás: si bien el ladrillo sigue por encima de los demás materiales de estudio, el jardín por el contrario tiende a una temperatura similar a la del ambiente, por lo cual no acumula tanta radiación a lo largo del tiempo. El estudio de Kaiser y Köhler [37] afirma que la implementación de coberturas vegetadas como aislantes térmicos controla el efecto isla de calor.…”