2NDNATURE, 500 Seabright Avenue, Santa Cruz, CA 95062, USA.
Center for Sustainability Science, The Nature Conservancy, 10117 Berlin, Germany.
Sci Total Environ. 2022 Apr 15;817:152723. doi: 10.1016/j.scitotenv.2021.152723. Epub 2021 Dec 31.
Green stormwater infrastructure (GSI), which includes features like rain gardens, constructed wetlands, or urban tree canopy, is now widely recognized as a means to reduce urban runoff impacts and meet municipal water quality permit requirements. Many co-benefits of GSI are related to increased vegetative cover, which can be measured with satellite imagery via spectral indices such as the Normalized Difference Vegetation Index (NDVI). In urban landscapes, there remain critical gaps in understanding how urban greenness and GSI influence hydrology. Here, we quantify these relationships to assess the feasibility of tracking the effectiveness of urban greening for improving downstream hydrologic conditions. We combined hydrologic data from the United States Geological Survey (USGS) gauges with an NDVI time series (1985-2019) derived from Landsat satellite imagery, and synthesis of GSI implementation data from a set of 372 urbanized watersheds across the United States. We used a multivariate panel modeling approach to account for spatial and time varying factors (rainfall, temperature, urban cover expansion) in an effort to isolate the relationships of interest. After accounting for expansion of urban boundaries, only 32 watersheds (9%) showed significant greenness trends, a majority of which were reductions. Urban greenness had significant influences on downstream flow responses, so that on average, a 10% greenness increase showed a corresponding reduction of total flow (-3.8%), flow variance (-7.7%), peak flows (-4.7%), high flows (-7.6%), flashiness (-2.2%), and high flow frequency (-1.5%); and a corresponding increase in baseflow (4.3%). For a subset of these watersheds for which GSI data were available (n = 48), the level of GSI implementation showed a significant, but weak influence on urban greenness with a 20% increase in BMP density corresponding to a greenness increase of 0.9%. The study results may support valuation and verification of GSI co-benefits in urbanized landscapes at the watershed scale.
绿色雨水基础设施 (GSI) 包括雨水花园、人工湿地或城市树冠等功能，现已被广泛认为是减少城市径流影响和满足城市水质许可证要求的一种手段。GSI 的许多附带好处都与增加植被覆盖有关，可以通过卫星图像的光谱指数（如归一化差异植被指数 (NDVI)）来测量。在城市景观中，人们对城市绿化和 GSI 如何影响水文学仍存在理解上的关键差距。在这里，我们量化了这些关系，以评估跟踪城市绿化改善下游水文条件的有效性的可行性。我们将美国地质调查局 (USGS) 测量站的水文数据与 1985-2019 年期间从陆地卫星图像得出的 NDVI 时间序列相结合，并综合了来自美国 372 个城市化流域的 GSI 实施数据。我们使用多元面板建模方法来解释空间和时间变化因素（降雨量、温度、城市覆盖范围的扩大），以分离感兴趣的关系。在考虑到城市边界扩张后，只有 32 个流域（9%）表现出显著的绿化趋势，其中大部分是减少。城市绿化对下游流量响应有显著影响，因此平均而言，绿化增加 10%会导致总流量减少（-3.8%）、流量方差减少（-7.7%）、峰值流量减少（-4.7%）、高流量减少（-7.6%）、突发性减少（-2.2%）和高流量频率减少（-1.5%）；基流增加（4.3%）。对于其中一部分有 GSI 数据的流域（n=48），GSI 实施水平对城市绿化有显著但较弱的影响，BMP 密度增加 20%对应于绿化增加 0.9%。研究结果可能支持在流域尺度上对城市景观中 GSI 附带效益进行评估和验证。
