Low impact development technologies for mitigating climate change:Summary and prospects

Many cities are adopting low impact development(LID)technologies(a type of nature-based solution)to sustainably manage urban stormwater in future climates.LIDs,such as bioretention cells,green roofs,and permeable pavements,are developed and applied at small-scales in urban and peri-urban settings.There is an interest in the large-scale implementation of these technologies,and therefore assessing their performance in future climates,or conversely,their potential for mitigating the impacts of climate change,can be valuable evidence in support of stormwater management planning.This paper provides a literature review of the studies conducted that examine LID function in future climates.The review found that most studies focus on LID performance at over 5 km2scales,which is quite a bit larger than traditional LID sizes.Most paper used statistical downscaling methods to simulate precipitation at the scale of the modelled LID.The computer model used to model LIDs was predominantly SWMM or some hybrid version of SWMM.The literature contains examples of both vegetated and unvegetated LIDs being assessed and numerous studies show mitigation of peak flows and total volumes to high levels in even the most extreme climates(characterized by increasing rainfall intensity,higher temperatures,and greater number of dry days in the inter-event period).However,all the studies recognized the uncertainty in the projections with greatest uncertainty in the LID’s ability to mitigate storm water quality.Interestingly,many of the studies did not recognize the impact of applying a model intended for small-scale processes at a much larger scale for which it is not intended.To explore the ramifications of scale when modelling LIDs in future climates,this paper provides a simple case study of a large catchment on Vancouver Island in British Columbia,Canada,using the Shannon Diversity Index.PCSWMM is used in conjunction with providing regional climates for impacts studies(PRECIS)regional climate model data to determine the relationship between catchment hydrology(with and without LIDs)and the information loss due to PCSWMM’s representation of spatial heterogeneity.The model is applied to five nested catchments ranging from 3 to 51 km2and with an RCP4.5 future climate to generate peak flows and total volumes in 2022,and for the period of 2020–2029.The case study demonstrates that the science behind the LID model within PC stormwater management model(PCSWMM)is too simple to capture appropriate levels of heterogeneity needed at larger-scale implementations.The model actually manufactures artificial levels of diversity due to its landuse representation,which is constant for every scale.The modelling exercise demonstrated that a simple linear expression for projected precipitation vs.catchment area would provide comparable estimates to PCSWMM.The study found that due to the spatial representation in PCSWMM for landuse,soil data and slope,slope(an important factor in determining peak flowrates)had the highest level of information loss followed by soil type and then landuse.As the research scale increased,the normalized information loss index(NILI)value for landuse exhibited the greatest information loss as the catchments scaled up.The NILI values before and after LID implementation in the model showed an inverse trend with the predicted LID mitigating performance.

A critical literature review of bioretention research for stormwater management in cold climate and future research recommendations

Bioretention is a popular best management practice of low impact development that el/ecUvely restores urban hydrologic characteristics to those ofpredevelopment and improves water quality prior to conveyance to surface waters. This is achieved by utilizing an engineered system containing a surface layer of mulch, a thick soil media often amended with a variety of materials to improve water oualitv, a variety of vegetation, and underdrains, depending on the surrounding soil characteristics.Bioretention systems have been studied quite extensively for warm climate applications, but ctata strongly supporting their long-tema efficacy and application in cold climates is sparse. Although it is apparent that biorelention is an effective stormwater management system, its design in cold climate needs further research. Existing cold climate research has shown that coarser media is required to prevent concrete frost from forming. For spring, summer and fall seasons, if sufficient permeability exists to drain the system prior to freezing, peak flow and volume reduction can be maintained. Additionally. contaminants that are removed via filtration are also not impacted by cold climates. In contrary, dissolved contaminants, nutrients, and organics are significantly more variable in their ability to be removed or degraded via bioretention in colder temperatures. Winter road maintenance salts have been shown to negatively impact the removal of some contaminants and positively impact others, while their effects on properly selected vegetation or bacteria health are also not well understood. Research in these water quality aspects has been inconsistent and therefore requires further study.

寒冷地区高密度街区被动式节能设计策略研究

本文结合寒冷地区高密度街区的环境特征,从建筑布局形式、建筑单体设计、公园水体的低影响开发、公共交通环境的优化、慢行交通环境的改善、新能源的开发与利用、法律规范的制定以及宣传教育等方面提出了具有普适性的被动式节能策略,并构建寒冷地区高密度街区被动式节能策略体系,有望促进高密度街区的可持续发展。

不同城市功能区实施屋顶绿化的雨洪调控效应比较

全球气候变化及城市地表硬质化加剧了城市雨洪风险,屋顶绿化作为一种低影响开发措施,可有效削减暴雨径流,为雨水进入城市管网树立第一道屏障。本研究采用CITYgreen模型,模拟分析南京新、旧居住区和商业区实施屋顶绿化对地表径流等水文参数的影响,比较不同功能区屋顶绿化的雨洪调控效应差异,分析功能区内部不同屋顶绿化之间以及屋顶绿化与地面绿化的雨洪效应差异。结果表明:南京市典型老居住区、新居住区及商业区实施屋顶绿化可使透水面比例分别增加28.9%、12.5%和49.2%。在一次重现期2年历时24 h(雨量72 mm)的降雨事件中,3个样区所有建筑实施屋顶绿化可使地表径流量减少0~19.8%、洪峰流量下降0~26.5%,相当于建造了容量为223~2299 m^(3)的调蓄设施。3个样区实施屋顶绿化的雨洪调控效应排序为:商业区>旧居住区>新居住区;草坪型屋顶绿化的单位面积雨洪调控量相当于花园型的78.6%~91.7%;屋顶绿化的单位面积雨洪调蓄量为地面绿化的31%~43%。研究结果可为基于雨洪管理的屋顶绿化选址、可持续设计及激励措施制定提供科学指导。