Assessment of rooftop area for rainwater harvesting in densely populated city: advancing sustainable water management practices

Water is a crucial and indispensable resource, essential for a myriad of daily activities. In Dhaka, Bangladesh, the issue of water scarcity has reached alarming levels, underscoring the urgent need to explore new water sources. Despite the critical situation, there is still a significant gap in comprehensive research and identification of alternative water sources. In this context, a holistic approach including geographic information system was adopted, integrating multi-criteria decision analysis with the analytic hierarchy process, to meticulously assess the most viable zones and rooftops for effective rainwater harvesting. To evaluate the potential water yield through rainwater harvesting, the Soil Conservation Service Curve Number method was used to approximate the rainfall-runoff dynamics in the study area. The findings indicated that about 23% of the total area is highly conducive for implementing rainwater harvesting, whereas 62% and 15% of the areas were deemed moderately and poorly suitable, respectively. Results showed that among the 6291 existing roofs in the study area, approximately 10% fell into the good condition category for rainwater harvesting. Additionally, the rainfall-runoff estimation analysis revealed that during the wet seasons, harvested rainwater could potentially meet up to 40–59% of the total water demand of Dhaka's extensive population. Recognizing the potential of rainwater harvesting and its capacity to contribute to water demand empowers policymakers to devise strategies and policies promoting sustainable water usage. This effort is pivotal in conserving and efficiently using water resources, ensuring their long-term availability and resilience amidst escalating water demand and challenges.