Rooftop Rainwater Harvesting for Mosul City as Water Resources Using GIS

The collection of rainwater from rooftops is a sustainable and widely practiced technique in many countries. This approach is designed to capture rainwater from building roofs, enabling its storage and efficient use to address water scarcity in urban areas. In this study, Mosul is chosen as a case study for rooftop rainwater harvesting. An analysis of the city’s climate over a 30-year period (1984–2014) shows that the average annual precipitation was 352.1 mm. Using advanced software, the total rooftop area in the city is determined to be 63.292 Km², providing an accurate measure of the potential collection area during the rainy season. To estimate the rainwater harvesting potential, the Gould and Nissen formula was applied. The calculation reveals that rooftops in the study area could collect approximately 21.170 × 10⁹ liters of water annually. This corresponds to an estimated 39.42 liters per capita per day, which meets international standards. According to these standards, a daily per capita allocation of 20 liters is considered adequate to meet basic human water needs.