Spatiotemporal assessment of rainwater harvesting efficiency for multi-story residential buildings across different climate zones in China

Rapidly growing population and urbanization have led to serious urban water environment problems. Rainwater is increasingly recognized and utilized as a viable alternative water source in response to these issues. Rainfall pattern, tank size and water use scenarios significantly affect the efficiency of RainWater Harvesting (RWH) systems. To better compare and analyze the impacts of the above factors on the reliability and efficiency of RWH systems, this study conducted experiments in three Chinese cities within different climate zones across three representative years (wet year, average year and dry year). Robust analysis was performed based on careful data pre-processing, which excludes irrelevant rainfall data. A computational tool was developed to evaluate the performance and reliability of rainwater management for RWH systems. Performance analysis and optimization of the RWH system for multi-story residential buildings based on a water balance model were conducted in three Chinese cities. We combined the roof catchment area, water tank volume, and rainwater utilization scenarios to obtain the rainwater harvesting efficiency, overflow ratio, water saving efficiency, and reliability charts of RWH system. In cities with large rainfall (Wuhan), before the maximum rainwater collection size is reached, increasing the tank size can significantly enhance the efficiency of the RWH system. In cities with average or low rainfall (Xi'an and Xining), the maximum rainfall storage capacity of the tank is easily reached, so rainfall is the main factor affecting the efficiency of the RWH system. Meanwhile, the water use scenario is the main factor affecting the reliability of the RWH system in cities with average or low rainfall. Demand scenario critically determines reliability—irrigation (B) achieves high reliability (up to ∼78 %), whereas toilet flushing (A) or combined use (C) exhibit much lower reliability (as low as 2.74 %) due to demand exceeding supply. Results of the study provide decision support for urban water authorities to effectively mitigate urban water supply deficiencies and urban flooding risks. • Proposed a framework for interannual rainfall variability and RWH performance under extreme conditions. • A daily water balance model quantified RWH efficiency, water savings, overflow ratio, and reliability. • Cross-climatic analysis identified region-specific RWH drivers; demand scenarios key to optimal design.