Rainwater harvesting potential in water abundant and scarce regions in northeast Brazil using remote sensing

Population growth, industrial development, and anthropogenic activity footprints are directly related to water scarcity and deterioration. Therefore, a sustainable water supply is highly desired, especially in regions where rainfall is not temporally constant. Rainwater harvesting (RWH) makes use of rooftops as catchment areas, and the harvested water can be directly used for non-potable purposes or treated to meet drinking water standards. High-resolution satellite images can be used for roof area approximations and identifications, which makes remote sensing an important tool for evaluating the RWH potential. In this study, digital elevation and digital terrain models can be used in conjunction with the normalized difference vegetation index to calculate the roof catchment areas in Palmares and Caruaru, which are cities located in Pernambuco State, Brazil. In addition, roofs were manually vectorized in a selected urban region in Palmares to validate the proposed method results. Because of the vegetation noise observed in rural areas, which significantly affected the roof area calculation, the analysis was limited to the urban areas of Palmares and Caruaru. Based on the rainfall volume and potable water demand for each city, the potential for potable water saving values were 51.1% and 44.4% for Palmares and Caruaru, respectively, indicating that RWH is capable of reducing pressure on the public water supply system. Furthermore, the proposed method improved previous RWH calculations and can be easily replicated in other regions.