Stress testing eight water tank metrics under the different energy zones in South Africa to evaluate how future climatic variations may affect rainwater harvesting

Introduction In its 2023 report, the Intergovernmental Panel on Climate Change (IPCC) reported Q8 Q9 that global surface temperatures during 2011–2020 were, on average, 1.1 °C higher than during the 1850–1900 period, which led to losses and damages that included decreased physical water availability and reduced agricultural food production. These effects were manifested through droughts in South America and Southern Africa. The practice of affordable, energy-efficient water conservation is, therefore, highly necessary in South Africa amid these negative effects of climate change and increasing costs resulting from higher energy costs. The purpose of this research was to evaluate the effects of changes in temperature and precipitation on the resilience of rainwater tank systems by analyzing their effects on the elasticities of tank metrics, such as system efficiency, optimum tank size, and lifecycle energy and emissions. Methods The research employed time series analysis and stress testing using the generalized simulated annealing technique. The research study area encompassed the whole of South Africa. Results The results indicated that the lifecycle energy and emissions of the rainwater tank system in the eastern coastal areas were marginally affected by likely changes in annual precipitation and mean annual temperature, as evidenced by zero or near‐zero precipitation and temperature-related elasticities of lifecycle energy and emissions at high domestic rainwater treatment energy intensities (up to 1.6 kWh/ m 3 ). However, when the treatment energy intensities were low (0–0.4 kWh/m3), although temperature-related effects were marginal in these areas, the precipitation‐related effects were greatest in these eastern coastal areas, with greater increases in precipitation leading to larger reductions in the lifecycle energy of tank systems (from –667.94 to –13,668.40 MJ/unit precipitation scale ratio). Discussion Generally, the eastern areas of South Africa had greater absolute values of tank metric elasticities than the western areas (especially the Northern Cape) which means they would experience greater impacts due to climate change. Energy Zone 6, followed by Zone 2, Zone 5, and Zone 5H, benefited the most from increases in annual precipitation and mean annual temperature (more impacted by climate change), while Zone 7, followed by Zone 4, Zone 3, and Zone 1, benefited the least (less impacted by climate change).