降雨变化对雨水收集系统节水及径流的调控效应

Impacts of rainfall change on water saving and runoff control performance of rainwater harvesting systems

雨水收集利用是城市水土保持的重要措施之一,具有缓解城市水资源短缺、减轻城市供排水系统压力等功能,被广泛应用于海绵城市和节水型城市建设。基于福州与乌鲁木齐1965-2015年实测日降雨量数据,分别采用回归分析和CLIGEN模型对21个GCMs预估月降雨数据进行空间和时间降尺度转换得到2020-2050年日降雨量数据,并基于自主构建的雨水收集系统水文模型,分析未来降雨变化对雨水收集系统节水及径流调控效应的影响。结果表明:福州与乌鲁木齐2020-2050年的年均降雨量比1985-2015年分别增加2. 7%和28. 2%,雨水收集系统节水效应(供水保证率和自来水替代率)明显增强,而径流调控效应(径流削减率)有所降低;降雨变化对雨水收集系统节水及径流调控效应的影响与气候区、汇水区面积、蓄水池容积等因素有关;降雨增加对节水效应产生积极影响,而对径流调控效应产生消极影响;降雨量较少的城市雨水收集系统对降雨变化更为敏感,汇水区面积和蓄水池容积越大的雨水收集系统对降雨变化的适应性越强。

[Background] Rainwater harvesting,as one of the important soil and water conservation measures to alleviate shortage of water resources and to relieve pressures on water supply and drainage systems in urban areas,has been increasingly used as an effective practice for the Sponge City and Water Saving City construction. Design and construction of rainwater harvesting systems should meet future water demand scenarios and rainfall conditions,however,most of current studies of rainwater harvesting systems use only historical climate and water demand data. Rainwater harvesting systems designed with historical data may not be able to sustainably meet water saving or stormwater management requirements under future climate conditions. [Methods] In this study,the plausible impacts of rainfall change on water saving and stormwater management performance of rainwater harvesting systems were investigated by comparing the water supply reliability(g),tap water saving efficiency(w) and runoff reduction efficiency( η) of rainwater harvesting systems in Fuzhou and Urumqi calculated using the future( 2020-2050) and historical( 1985-2015) daily rainfall time series. A downscaling technique based on linear and nonlinear regression analysis and the CLIGEN model was evaluated and employed to generate the future daily rainfall with the projections of 21 Global Circulation Models. A daily water balance model was developed to simulate the hydrologic operation of rainwater harvesting systems. Toilet flushing water demand was considered in this investigation. [Results] The simulated rainfall data of Fuzhou and Urumqi from 1960 to 2005 using the regression analysis for spatial downscaling and the CLIGEN model for temporal downscaling is close to the measured rainfall data. The downscaling technique performs well in simulating the occurrence of daily rainfall at both of the cities. Therefore,the CLIGEN model could alternatively be used at Fuzhou and Urumqi for rainwater harvesting system analysis. The downscaling rainfall data shows that mean annual rainfall in Fuzhou and Urumqi in 2020-2050 is going to increase by2. 67% and 28. 23% compared with that in 1985-2015,respectively. The water saving performance of rainwater harvesting systems is positively affected by the increases in future rainfall, as rainwater harvesting systems with smaller tank sizes and/or smaller catchment areas could supply adequate water for demand at a desired tap water saving efficiency or water supply reliability. The stormwater management performance,however,is negatively affected under the conditions of future rainfall change,as a larger tank size or larger catchment area is required to achieve desired runoff reduction efficiency.[Conculsions] The responses of water saving and stormwater management performance of rainwater harvesting systems to rainfall change are varying with not only the system dimensions( i. e.,storage capacity and catchment area),but also locations with different rainfall conditions. Rainwater harvesting systems in a drier city with less rainfall are more sensitive to rainfall change. Rainwater harvesting systems with larger storage capacity and/or larger catchment area are expected to be more resilient to rainfall change. Therefore,the ability of rainwater harvesting systems to adapt to rainfall change could be increased by designing larger reservoirs and catchment areas.