The amenity value of constructed wetlands

Natural wetlands in urbanised areas provide practical services, including flood control and amenity values such as views, wildlife habitat and recreational opportunities. But cities also construct wetlands to improve flood control and ecosystem services, the value of which might change property prices. This paper reports analyses of property prices that provide estimates of wetlands' localised amenity values in Auckland, New Zealand's largest city. A major challenge is that the selection of sites for wetlands’ construction is not random; amenity value is potentially confounded by property and neighbourhood characteristics that vary across space and over time. We use a combination of repeat-sales models, difference-in- differences and matching models to control for unobserved heterogeneity in property and neighbourhood characteristics. The results indicate that local benefit from constructed wetlands ranges from about 5% to 9% depending on the location of the property in areas adjacent to the wetlands or in a larger catchment of interest. Our results have a causal interpretation if the selection criteria are applied uniformly across Auckland and are valuable in assessing the benefits of constructed wetlands.城市化区域内的天然湿地可提供多项实用服务功能，包括防洪，以及观景、野生动物栖息地、休闲机会等舒适性价值（amenity values）。不过，城市也会人工建造湿地以提升防洪能力与生态系统服务水平，这类湿地的价值可能会对房地产价格产生影响。本文以新西兰最大城市奥克兰为研究区域，通过分析房地产价格，估算了当地湿地的局地舒适性价值。本研究面临的一项核心挑战在于，湿地建造的选址并非随机进行；房地产与邻里特征会随空间与时间发生变化，这可能会对舒适性价值的估算造成混杂偏倚。为此，本文结合使用重复销售模型（repeat-sales models）、双重差分模型（difference-in-differences）与匹配模型（matching models），以控制房地产与邻里特征中的未观测异质性。研究结果显示，人工湿地带来的局地收益约为5%至9%，具体数值取决于房地产区位：要么位于湿地毗邻区域，要么属于研究关注的更大流域范围。若奥克兰全市统一应用该选址准则，则本研究结果具备因果解释效力，可为人工湿地的效益评估提供重要参考。