Into the air: a freestanding vertical greenery system (VGS) for evapotranspiration (ET) of roof runoff

In the search for space-efficient nature-based solutions (NBS) for stormwater management, we designed a vertical greenery system (VGS) for enhanced evapotranspiration (ET). After assessing a range of construction options, an 80 m long and 3.2 m high freestanding stormwater-VGS, referred to as the Green Climate Screen (GCS), was constructed in 2019 in Copenhagen. The GCS receives runoff from 240 m(2) of roof top and has a high ratio of surface-to-ground area to allow for the clothesline effect to enhance ET. The conveyance of runoff to the top of the GCS is based on gravitational force. It is estimated that 24 h events with return periods up to the 0.1 y (13.9 mm) are managed by ET, from 0.1 to 15 y (48.5 mm) by infiltration beneath the screen, and from 15 to > 100 y by overflow to an adjacent area allowing for aboveground storage (167 mm), in total 229 mm. With the fulfillment of most performance criteria and successful inclusion of selected co-benefits ET-based stormwater, NBS could become future standard elements. To reduce CO2 and resource footprint, steel, concrete, and mineral wool must be replaced with renewable materials. Adaptation to more spatial contexts is encouraged.