Rainwater Use for Vertical Greenery Systems: Development of a Conceptual Model for a Better Understanding of Processes and Influencing Factors

Abstract

Vertical greenery systems (VGS) are promoted as a nature-based solution to mitigate the urban heat island effect. In order to ensure the long-term provision of this function, sufficiently available irrigation water is the key element. Currently, potable water is one of the main resources for irrigation of VGS. While rainwater is often mentioned as an alternative, only a few studies investigate the actual application of rainwater for irrigation. In this study a conceptual model is developed to present the processes and influencing factors for a holistic investigation of rainwater use for irrigation. In this model, five sub-modules are identified: the atmospheric, hydraulic, quality, rainwater harvesting and VGS sub-module. The conceptual model depicts which processes and influencing factors are involved in the water demand of VGS. Thus, the conceptual model supports a holistic understanding of the interrelations between the identified sub-modules and their relevance for VGS irrigation with harvested rainwater. The results of this study support the implementation of rainwater harvesting as a sustainable resource for VGS irrigation.

Closing Water Cycles in the Built Environment through Nature-Based Solutions: The Contribution of Vertical Greening Systems and Green Roofs

“…For VGS, some literature demonstrates the potential of rainwater use [46,47], but detailed experimental investigation is scarce [48]. Rainwater harvesting systems have proven to be effective as partial substitutes for domestic water demand in oceanic zones [49], as well as in semi-arid climatic zones [50], but limiting factors include the unpredictability of precipitation patterns and the size of water storage systems, which may be prohibitive [14]. On the other hand, wastewater, particularly greywater, is produced daily and, hence, can provide a continuous stream of irrigation water once treated.…”

“…Greywater (household wastewater without the toilet stream) has proven to be a viable resource for irrigation, and the necessary treatment can be done by judiciously employing on-site systems, such as pot-based green facades and GRs [12,13]. In addition, water via rainwater harvesting can be reused for irrigation [14].…”

“…Plant water consumption must be met throughout the year to allow for the full spectrum of multifunctionality, e.g., increasing biodiversity, contributing toward public health, decreasing air pollution, and cooling the surrounding area [6]. This "demand" is mainly met with fresh water or drinking water, further contributing to water depletion [14]. However, operational water demand is not the only important factor in water reuse practices.…”

Observation Experiment of Wind-Driven Rain Harvesting from a Building Wall

“…In the case of tall buildings, the amount of rainwater to be harvested from the wall could be more than that from the roof. To date, a building wall has only been considered for urban greening [41][42][43][44][45][46]. Samzadeh et al [47] estimated the level of rainwater harvested from the building wall by applying an empirical equation, but a direct observation of the rainwater from the wall has not been conducted yet.…”

Water and Circular Cities

“…Additionally, to evaluate the level of circularity of resources' management in cities, appropriate indicators are proposed by the COST Action and presented in this Special Issue [7]. Other papers included in the Special Issue focus on several aspects of using NBS for creating circular economies in cities, i.e., green roofs and vertical greenery systems [8,9]; production of food in cities [10,11], vacuum toilets generating blackwater [12] as well as biogas plants [13].…”