Aaron Kauffman (SW Urban Hydrology and previous Land and Water Summit speaker/tour guide) and Cody Stropki (SWCA Environmental Consultants) just published a study on soil moisture in Santa Fe rain gardens over a seven year period. It presents some excellent data to make the case for rain gardens. Definitely worth a read and please share!
Kauffman, A. T., & Stropki, C. L. Green stormwater infrastructure in a semi-arid climate: The influence of rain gardens on soil moisture over seven years. The Western Planner. November 7, 2022.
- 2NDNATURE, 500 Seabright Avenue, Santa Cruz, CA 95062, USA
- Center for Sustainability Science, The Nature Conservancy, 10117 Berlin, Germany
- The Nature Conservancy in Colorado, 2424 Spruce Street. Boulder, CO 80302, USA
- The Nature Conservancy, 322 8th Avenue, New York, NY 10001, USA
- Green stormwater infrastructure (GSI) is shown to affect urban greenness patterns.
- Urban greenness is shown to influence a range of downstream hydrologic responses.
- Only 9% of watersheds show significant trends in satellite-measured urban greenness
- Detection of broad, watershed-scale GSI impacts is limited by GSI data completeness.
Received 10 September 2021
Received in revised form 21 December 2021
Accepted 23 December 2021
Available online 31 December 2021
Editor: Ashantha Goonetilleke
Keywords:
Stormwater
Hydrology
Urban greenness
Green stormwater infrastructure
NDVI
Panel regression
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.
