The challenge of increasing urban vegetation in water-restricted environments

Urban vegetation mitigates solar radiation, absorbs noise and greenhouse gases, releases oxygen and filters suspended particles, among other benefits, but the growing urban demographic explosion represents an assault on the availability of green spaces in big cities.

One alternative to increase ‘urban greening’ is the development of new techniques to incorporate vegetation on the roofs and walls, like green roofs. A group of researchers of the Institute of Human, Social and Environmental Sciences (INCIHUSA-CONICET), at the CCT Mendoza, explores and designs technologies to increase urban vegetation in cities with semi-arid climates such as Mendoza.

“As it happens in several cities, this region undergoes an unplanned growth process that undermines Mendoza’s basic urban conception, characterized by multiple parks and trees along the avenues”, explains Alicia Cantón, a CONICET associate researcher and director of the research project financed by the National Agency for the Promotion of Science and Technology.

One option to help mitigate this problem, even in the case of semi-arid climates such as in the province of Mendoza, could be to develop of new technologies in order to incorporate vegetation on roofs and walls like green roofs. “Worldwide, this new tendency proved to be a viable alternative that impacts not only upon the reduction of the effects of global warming, atmospheric pollution and noise levels, but also on the reduction of the urban heat island effect and the thermal conditioning of the buildings. This can reduce energy consumption between 35-95%, according to the amount of vegetation and the climate of the region”, Cantón highlights.

Which are the specific goals of this project?

The idea is to develop technologies adapted to arid areas and quantify their benefits, not only in environmental but also in economic terms, in order to provide information for the promotion of private and local investment in terms of vegetation. For instance, in Washington DC the annual benefits associated with the afforestation of the roads is the equivalent of USD 1 million between energy-saving, absorption of carbon dioxide, improvements of air quality, flood reduction and increase of aesthetic value.

What does this new green technology consist of?

These modules are placed on roofs and walls as a support material to incorporate green surfaces on different facilities. The roof modules include a technology and a biological package. The first is related to the constructive part of the base, whereas the second is inherent in the type of vegetation and the irrigation system. In general, the set comprises a waterproof coating, a draining layer, a growing substrate and plant species. From the experimental trials of different systems, this project will be used to develop low-cost technologies that can adapt to strict environmental conditions – water deficit and low water consumption plant species – to promote its massive implementation in the region.

Is it possible to use these techniques to improve the relationship between vegetation and city cement under an increasing building growth rate and water scarcity scenario, such as in Mendoza?

In our country, the interest for these technologies is recent and it is limited to the drafting of legislations, programmes, reports and its use on remarkable works. In the case of arid areas with scarcity of water, its implementation includes an additional challenge for the need to reconcile the benefits of the incorporation of a high impact strategy in the urban-building conditions, with the great demand for water resulting from the maintenance of green spaces. Recent reforms in the building code of the cities of Mendoza and Godoy Cruz foresee a significant impact on the density of urban fabric. From the point of view of sustainability in an urban model of an ‘oasis city’ inserted in a highly vulnerable ecosystem, the building growth has to be accompanied by a growing presence of green spaces, and thus the importance of our proposal.