Exploring Urban Rainwater Harvesting in the city of Madrid applying GIS based MCDA expert tools

Abstract: Due to climate change, water resources’ scarcity and distribution variability have generated a growing interest in sustainable water management in recent years. In addition, the growing interest in implementing nature-based solutions for urban resilience leads to the development of decentralized water supply systems such as rainwater harvesting systems (RWHS) as a complementary resource to conventional centralized water supply systems. The study is motivated by the climatic risks that the city of Madrid is subject to face in the upcoming years such as pronounced summer droughts and urban heat waves, leading to the reduction of water resources availability. This study aims to use Multi-criteria decision analysis and Geographic Information systems as tools for locating optimal space for the installation of pond harvesting systems (PHS) in Madrid for water recollection for non-potable purposes in the city. Attaining this aim, two objectives were set. Firstly, to evaluate and select the most relevant criteria for the installation of PHS and secondly, to generate a map of the most suitable locations for installation of PHS in the city of Madrid through a proposed GIS-MCDA methodology and a complimentary evaluation for each possible solution, to obtain a global vision of the applicability of PHS in Madrid. Through the first objective, several criteria were set for PHS installation, namely: distance to the river, rainfall, slope, soil characteristics, and land use. These criteria were applied to Madrid through a GIS-MCDA methodology, using these two tools’ synergy to obtain a suitability map for PHS installation. Two criteria weightings will be performed to evaluate the model’s robustness by modifying the criteria’ weights resulting in two different suitability scenarios. The discussion will analyze the results obtained considering the two scenarios and propose the most suitable location clusters identified. Finally, the conclusion will reflect the study’s most important findings and open the door to further research on the topic, such as the design, operation infrastructure, drainage logistics distribution, and other modifications in Madrid’s current water management system.