Using rainfall measures to more accessibly evaluate resilience of rainwater tanks under climate change

Climate change is altering rainfall and raising concerns over whether rainwater harvesting systems, typically designed using historical records, will remain reliable over their lifetimes. While researchers have begun evaluating rainwater tank performance under future climates, practical design guidance remains limited because reported reliability outcomes depend heavily on the specific configurations adopted in individual studies. Consequently, practitioners remain reliant on modelling or monitoring for independent future climate risk assessments. As these approaches may not always be feasible, this study proposes that tank resilience could instead be assessed using simple rainfall measures. High-resolution climate projections for Victoria (Australia) were used to first characterise climatic futures, then simulate a range of residential system configurations across the near-future (up to 2045) and historical baseline (1981–2010). Dimensional analysis was subsequently applied to 95% reliability outcomes to factor out the influence of system configuration, such that performance differences between periods reflect projected rainfall changes. Results indicate that tanks in low-rainfall regions (280–460 mm mean annual rainfall) are most vulnerable, exhibiting the most pronounced performance declines in response to further reductions in rainfall amount. In contrast, tanks in higher-rainfall regions (460–1070 mm mean annual rainfall) generally remain robust, although some vulnerability emerges when rainfall reductions coincide with decreased intra-annual distribution. For Victoria, this provides a more accessible approach to resilience assessment using rainfall amount and distribution. For locations with differing rainfall characteristics, this establishes a replicable framework whereby a one-off regional analysis supports routine assessment using readily available rainfall data.