Localized effects of daily persistence of rainfall on rainwater harvesting system’s reliability

Abstract:

Rainwater harvesting is not uncommon in water management practices around the world. It supports sustainability in water resources management and helps to reduce runoff generation. Rainwater harvesting system is attractive as it provides a long-term sustainable solution that reduces dependency on the main water supply system. Despite the theoretical reasoning of its usefulness, it is still unclear to what extent the system would be reliable given the climate uncertainty and weather variability. This study runs multiple possible dry and wet years to investigate the effects of daily rainfall persistence and variability to the rainwater harvesting system’s performance. Records of daily rainfall from a station in Selangor, Malaysia were analysed for wet and dry years. Auto-regressive lag-1 model, AR(1) was then used to generate the daily persistence rainfall of wet and dry years, respectively. A behavioral model that encapsulates the water balance of the rainwater harvesting system with realistic design parameter values were used to represent an institutional non-potable water usage of the system. Results show that the reliability of the system could drop as low as 14% in dry years, but would maintain on average 46% reliability. The average reliability of the dry years is only 7% lower than the average reliability of the wet years, despite that the total rainfall of the actual dry year is only half of the total rainfall of the actual wet year. The results indicate that persistent dry days in a year would not cause significant reduction to the system's reliability for the institutional non-potable water usage in the area. Similar studies to other parts in the tropical region and spatial setting could lead to a greater understanding on the system's reliability on a larger scale. This may promote a greater uptake of the system and lead to a long-term sustainable solution in water management.