ROOFTOP RAINWATER HARVESTING in MODERN CITIES: a CASE STUDY for SANA’A CITY, YEMEN

الملخص

Water resources in Yemen are limited, and water is becoming scarce everyday due to ever-increasing demand due to the rapidly increasing population and to the drought climate the country is characterized with. Increasing overdrawn from groundwater causes a deficit of 900 Mm3 annually leaving the country to seek alternative resources. All major cities in Yemen facing water problems resulting in a mainly socio-economic change –beside other challenges-that produce unrest and unforeseen conflicts to acquire water when needed
especially in the capital city of Sana’a where groundwater levels drop annually by an average of 6 m. Rainwater harvesting systems have been used since ancient times and evidence of roof systems date back to more than 4000 years ago in the middle east as the principal water source for drinking and domestic use. This paper summarizes the findings of a substantial work by the authors during the past three years in providing a reasonable, alternative solution to the water scarcity problem through dealing with water harvesting as an alternative resource. This paper estimated the amount of water that can be harvested annually from roof tops 11.31 Mm3 for urban areas using runoff coefficient of 0.75 and 0.172 Mm3 for rural areas using runoff coefficient of 0.6. This indicates that there will be an annual reduction in the usage of groundwater in urban and rural areas by 22% and 33% respectively. Simple and easy harvested water volume guide tables were developed for different run off coefficients of 0.6, 0.7, 0.75 and 0.8. It also presents a the main factors for the design of a complete Rooftop Rainwater Harvesting System for the city of Sana’a.