Snösmältning och avrinning från gröna extensiva tak
Green roofs are a popular way to include nature in an urban environment. How is runoff from green roofs in the cold and snow-covered part of the year, when growth media freeze, plants are dormant and covered with melting snow? This paper investigates 11 years of runoff from three green extensive roofs in Oslo, Norway. Precipitation through the snow-covered period (SCP) was approx. 1/3 of the annual precipitation (970 mm). When runoff from green roofs is compared to runoff from a non-vegetated bitumen roof, a retention of 16 –31% is seen through the SCP, depending on drainage system, fabric, soil quality and depth. The difference in buildup did not influence the detention of the largest runoff intensities. Dampening the runoff happened even though the substrate was saturated. The runoff from the bitumen roof always exceeded the runoff from the green roofs. As a result, harmful inundation may be reduced in a part of the year when infiltration is restricted due to frost.