Microclimatic conditions of 'Green Walls', a new restoration technique for steep slopes based on a steel grid construction

The greening of shotcrete walls represents a major challenge due to the extreme environmental conditions for plants and its technical implementation aiming to establish a sustainable vegetation layer. The objective of the study was to assess the performance of an innovative 'Green Wall' system (double-layered, integrated irrigation, filled with excavation material, application on vertical inclination) with respect to its microclimatic characteristics.The measurement campaign was conducted from June 2015 to September 2016 in Plon (Steinach am Brenner, Tyrol, Austria). Microclimatic parameters (air temperature, air humidity, short-wave radiation, substrate temperature and wall surface temperature) were investigated by sensors installed in different layers of the greenery system, as well as in a control area (bare concrete wall).Results indicated a pronounced insulation effect of the 'Green Wall' system during summer and wintertime. Analyses in July 2015 (30% vegetation cover) and July 2016 (100% vegetation cover) indicated that reductions of temperature fluctuations were predominately attributable to the substrate layers of the greenery system and less to the vegetation cover. Furthermore, reductions of albedo (reflectivity) and heat stress were achieved.In conclusion, the 'Green Wall' system is a promising technique with positive effects regarding temperature and radiation as well as human thermal sensation and therefore recommendable for use also in urban areas. In rural areas it helps to optimize landscape aesthetics, as even vertical slopes can be greened.