Qualidade da água de telhados verdes na cidade de Natal/RN: análise do pH, condutividade elétrica e turbidez

Abstract

Green roofs have emerged as an alternative to the minimization of the problems caused by urban development. Its structure brings benefits to the environment and especially to the population. Researches around the world converge on a truth about green roofs: They need to be adapted to the weather of each location in which they are built. Thus, through three different models, this research deals with the quality of the water drained of extensive green roof modules, composed of local materials (substrate, vegetation and other components) and subjected to the natural occurrences of precipitation in the city of Natal / RN, which is representing other Brazilian cities with a humid coastal climate. For this, a study was carried out on the climate of the city and the rainy season, based on a historical series of 30-year precipitation data from National Institute of Meteorology (INMET) and data of 3 years and 3 months of a pluviograph of the Federal University of Rio Grande do Norte, UFRN (the pluviograph was called PUFRN). In addition to the climatology of precipitation of the city, Extreme Events of Precipitation (EEP) were also studied, using a statistical technique of quantiles, and rainfall quality, represented by three parameters: potential of Hydrogen (pH), electrical conductivity (EC) and turbidity (Turb). These same parameters were analysed for the water drained of a green roof and compared to the ones obtained from the rainfall water on an impermeable surface. As result of the climatological study, it is observed that the rainy season for Natal/RN is concentrated from March to July and, in average, it rains 1000 mm in this period. June is the month with the highest volume of rain, although in the year 2017, it rained more in July. The threshold value for a daily EEP is 42.8 mm. During the period of April 2014 to July 2017, Natal/RN registered 27 EEP. The maximum intensity was 35.05 mm/h and it was necessary at least 2 hours for a precipitation become extreme. Most EEPs in Natal/RN take 6 hours to occur. The most frequent consequence of this type of occurrence are floods around the city. Regarding the quality of rainwater, for the last 10 years the parameters are the same and when compared to the parameters of the green roof water, it is noticed that the soil substrate is the major responsible for changing the parameters. An interesting fact about the modules used is that the ones with vegetation do not require watering during the rainy season.