Produção agrícola sobre as coberturas das edificações no espaço urbano e as possibilidades de impacto na segurança hídrica

Abstract

The urban development has not always been in the ways of sustainability. Among the problems associated with urbanization and water resources are the increase in water consumption, the increase in the volume of effluents and the increase of impermeable areas. The latter may contribute to an increase in the occurrence of floods. In this sense, there has been much discussion in the literature about Low Impact Urban Development (LID), involving practices called green infrastructures, such as green roofs (GR). GRs, in addition to contributing to rainwater retention and flood control, have other impacts and allow the practice of urban agriculture. In turn, urban agriculture has an impact on increasing food security, generating jobs and income, as well as reducing the burning of fossil fuels, since the distance between the producer and the consumer market is reduced. Despite these benefits, the introduction and subsistence of vegetation on roofs, especially for agriculture, may imply higher water consumption and also the generation of nutrient-rich effluents. Recently, the Southeast and Northeast Regions of Brazil experienced a severe water shortage. There is also concern worldwide about the impacts of climate change and its repercussions on water security. The main objective of this research was the evaluation of the efficiency and the water consumption in a productive system of low cost, for the practice of the urban agriculture in rooftops. The research, with in situ experimental characteristics, was developed in the rooftop of the fifth floor Rector Haroldo Lisboa building of the State University of Rio de Janeiro (Maracanã Campus). Different productive arrangements were tested on fiber cement tiles. The selected species was the "Brazilian Amanda" green-leaf lettuce (Lactuca sativa), which was cultivated in a different way in different productive arrangements. For the evaluation of the efficiency of the productive arrangements, the total fresh mass and stem diameter were evaluated, submitted to the statistical treatment "F" of ANOVA and Tukey-Kramer test. In addition, space, weight, cost of materials involved and water consumption were analyzed. In the three cycles developed and in all treatments it was obtained good productivity of plants with characteristics that meet commercial standards and possibilities of economic return. The sets were lightweight, suitable for the tiles, and at low cost. The quantities of water applied for the production of a unit of fresh lettuce mass were lower than those practiced in other production systems and advantageous from the standpoint of the lettuce water footprint. The study opens a range of new researches on other adapted vegetable species, microbiological and toxicological quality of the products produced, rainwater harvesting, reduction of energy consumption, closure of the "water supply-drainage circuit" with effluent collection and treatment, reduction of runoff and flood control in urban catchments.