Climate change is leading to more extreme precipitation events, which require new ways of managing stormwater, particularly in urban areas. Nature-based solutions (NBS) have become an increasingly popular way of providing additional stormwater retention and detention, as well as supporting urban biodiversity and access to nature. However, monitoring of the hydrological performance of NBS is often limited. To date most literature has focused on monitoring methodologies for specific sites and types of NBS, using remote sensing and modeling methods, or measuring benefits of NBS for urban heat mitigation. More comprehensive measurement strategies are needed to improve design, inform maintenance, and provide data that can encourage the adoption of NBS. To address this gap, this tutorial review provides specific recommendations for the instrumentation and in situ monitoring of common types and scales of NBS, as well as in-depth discussion of monitoring methods and hydrological performance for two specific NBS installations in the Chicago region. Based on these findings, we make recommendations for consistent hydrological assessment of NBS and development of common metrics that allow for comparison regionally and across different types of NBS.

Climate change is expected to increase the frequency and severity of flooding in the Great Lakes region. In many cities, flood-control infrastructure is insufficient to protect against future climate conditions. Consequently, there is increasing focus on stormwater storage provided by urban greenspace, such as wetlands and prairies, but the ecohydrological behavior of these ecosystems is not well understood when they are embedded within cities. To improve understanding of hydrological connectivity between urban areas and natural greenspaces, we deployed a sensor network in Gensburg-Markham Prairie (GMP), a large intact prairie-wetland complex in south suburban Chicago. We used the resulting high-frequency time-series to assess surface-subsurface hydrologic dynamics between upland and low-lying wetland areas, interactions between the prairie and surrounding environment, and stormwater storage provided by the prairie. GMP’s hydrological dynamics are generally controlled by surface-groundwater interactions that vary seasonally. Rapid infiltration during and after storm events provides subsurface flow that stores considerable water, flattens storm hydrographs, and increases the wetland hydroperiod. Much of the stormwater input to GMP derives from the surrounding cityscape. Consequently, storage within the prairie-wetland system reduces and slows stormwater discharge to downstream urban communities. For a typical 5-year 24-hour storm with 10.9 cm of rain, GMP stores 77,100 m3, 64% greater than the estimated direct rainfall volume onto the prairie, yielding 30,000 m3 of off site stormwater storage. This improved understanding of ecohydrological dynamics in urban prairies and wetlands informs the design and implementation of green infrastructure to meet growing needs for stormwater management.

Simultaneous pressures of climate change and increasing populations in urban areas have resulted in new stresses on stormwater infrastructure. Altered precipitation patterns require robust and versatile management strategies for stormwater, resulting in increased consideration of greenspace as infrastructure for communities with significant flood risk. There is particular interest in natural, minimally-engineered green infrastructure (GI). Such greenspaces can be heterogeneous and difficult to characterize but are often straightforwardly modelled as black-box systems within a landscape. Many natural sites cannot be approached so simply due to highly permeable interfaces with surrounding landscapes and it is often impossible to monitor the surrounds at anywhere near the same spatial or temporal resolution as within the boundaries of a study site, resulting in uncertainty about the actual benefit of natural greenspace for adjacent communities. We explored water storage in an urban green space, identifying spatio-temporal patterns of internal dynamics to holistically understand site behavior. A dense sensor network in a prairie wetland nature preserve within the Chicago metro area produced 4+ years of high-resolution surface and subsurface water level, soil moisture, precipitation, and air and water temperature data. Responses to weather events in the short term and to climate-driven seasonal effects in the longer term are then described via the combination of GIS methods and signal processing approaches. Power spectral and cross-correlation analyses contribute understanding of relevant timescales for further investigation. Applying hydrograph analysis methods to water level time series yields important statistics about the response of water table elevations throughout the prairie complex, including baseflow elevations and relaxation times. These statistics are used to develop spatial maps of event response as a function of site properties and to identify seasonal effects. Understanding the expected response of stormwater storage in a natural greenspace to a precipitation event has valuable utility for conservation groups and stormwater management utilities. The synthesis of these methods contribute to development of planning tools for siting, design, and management of GI.