Economic feasibility assessment and parameter sensitivity analysis of rainwater harvesting systems in different climatic zones of China

Abstract

Rainwater is an important non-traditional water resource, and the economic benefits of rainwater harvesting and utilization vary considerably across different climatic conditions. This paper constructs typical rainwater harvesting (RWH) models based on road watering and green space watering reuse pathways, as well as typical flat water year and cistern emptying time in three distinct climate zones of China: Urumqi (located in a semi-arid area), Baoding (located in a semi-humid area), and Shantou (located in a humid area). Using the Infoworks ICM model, long-term simulations (30 years) were conducted to evaluate the economic advantages of rainwater utilization across these climate zones. The Particle Swarm Optimization (PSO) was employed to optimize the cistern volume by integrating Net Present Value (NPV) and Benefit Cost Ratio (BCR). Additionally, multiple nonlinear regression analyses were employed to quantify the relationship between various catchment subsurfaces and the optimal reservoir volume. Sensitivity analyses, including Sobol sensitivity analysis, were performed for parameters such as subsurface characteristics, water price, discount rate, and number of days for emptying the impoundment. The study results indicated that the change curves of NPV and BCR in all three cities exhibit an increasing and then decreasing trend with the increase of reservoir volume under different reservoir setup scenarios. The optimal volume of the reservoir could be articulated through the fitting equation that relates the green space ratio to the road ratio. The discount rate and water price significantly impacted the optimal volume of storage tanks, with the sensitivity of the parameter of the number of days of emptying of the storage tanks to the optimal volume being greater in Shantou, a city in a high humid area. Conversely, in Urumqi, a semi-arid area, the variation of the parameter of greenland rate had a greater sensitivity to the volume of storage tanks. These findings provide valuable insights for the design and implementation of rainwater harvesting and utilization systems, offering practical guidance for sustainable urban development.