A Synthesis of Climate Change Impacts on Stormwater Management Systems: Designing for Resiliency and Future Challenges

As the impacts of climate change become increasingly evident worldwide, there is a critical need to better understand the practical implications of these changes on water resources in the built environment. Of particular concern are stormwater management systems (SMS), which are on the front line of changes in rainfall patterns and include stormwater control measures (SCMs) and associated gray infrastructure (pipes, structures, and so forth). Part of this concern has arisen as climate change renders one of the key facets of urban drainage design—that of a stationary precipitation frequency distribution—questionable at best (Rosenberg et al. 2010; Kendon et al. 2014; Deb et al. 2019). Changes in the precipitation distribution upon which infrastructure conventionally was designed essentially equate to changes in the risk that communities bear with respect to flooding, property damage, and human safety (Ganguli and Coulibaly 2017). Whereas natural watersheds evolve and adapt to changes in climate over time, effectively increasing flow capacity through channel evolution processes, fixed-dimension gray infrastructure does not inherently possess the ability to adapt. In typical urban stormwater networks, vulnerabilities such as flooding arise as the capacity of components within the system are overwhelmed and runoff accumulates at the surface or follows unintended paths. Studies to date indicate that the response of drainage systems to projected climate change is site dependent, and the capacity of some systems is predicted to remain adequate (e.g., Denault et al. 2002), whereas increased flooding and sewer overflows are predicted in other systems (e.g., Horton et al. 2010; Semadeni-Davis et al. 2008; Moore et al. 2016; Hettiarachchi et al. 2018). Furthermore, increases in watershed-scale runoff pollutant loads are projected under the impacts of climate change (Alamdari et al. 2020). SCMs historically have been used, in some cases for decades or generations, to alleviate the deleterious effects of urban hydrology on nearby water bodies and to reduce pollutants transported in stormwater (Hogan and Walbridge 2007). Although potentially a valuable tool for building resilience to climate change, these systems themselves also may be at risk of shifts in performance as new weather patterns emerge (Alamdari et al. 2020).

Climate change has several disruptive effects on SCM performance. These changes are highly spatially variable across large landscapes (Gao et al. 2012). For example, in the US, regions such as the desert Southwest, are anticipated to face prolonged droughts (USGCRP 2018), whereas the north-central and northeast regions of the US are projected to receive higher-intensity precipitation (USGCRP 2018). Temporally, changes in precipitation patterns across seasons also are expected, e.g., in the Great Lakes region (Hayhoe et al. 2010). Shifts in the precipitation phase from snow to freezing rain or rain also are expected as air temperatures increase (Tohver et al. 2014; Zaquot 2022). Other regions of the US (e.g., the Pacific Northwest and arid Southwest) are projected to experience minimal changes in typical annual precipitation, but rather significant increases in the frequency of extreme rainfall depths (Swain et al. 2018). In addition to precipitation depth, the intensity of events is expected to increase across much of the country (Tohver et al. 2014). Also relevant to SCM function is the dry-period duration (i.e., interevent period length) coupled with warmer temperatures which will add additional drought stress to the biotic components of these systems. Such elongated dry periods result in nutrient flushing in some types of SCMs due to microbial community disruptions and the breakup of soil aggregates (Manka et al. 2016).

Storm sewers, SCMs, and other urban drainage structures often are designed based on historical rainfall data, such as NOAA Atlas 14 (Perica et al. 2018), whereby specific storms of interest [e.g., a water quality event, a critical discharge-inducing event in a receiving stream (Hawley et al. 2016), or an infrequent return interval event] are used to inform the design characteristics of the system. Conventional approaches generally have not considered or integrated climate adaptation into designs, potentially resulting in underperformance over the long term. Many regulatory agencies also target specific pollutants of concern to be removed by SCMs, such as total suspended solids, nutrients, or heavy metals (WADOE 2019; MPCA 2022). The removal of specific pollutants in SCMs occurs through infiltration, filtration, biological processes, adsorption, and so forth, all of which can be substantially affected by changes in runoff hydrology, atmospheric conditions, and increased wash-off of pollutants from climate change–induced increases in rainfall intensity. In the age of climate nonstationarity, stormwater engineers and decision makers need to know (1) how current SMS and SCM designs will function under future climate scenarios, (2) what design modifications are needed (e.g., at a local or regional spatial scale) to ensure that SMS and SCMs are providing the desired level of service and are thus resilient to climate change, and (3) what factors are critical to consider regarding climate change. Herein, we summarize the state of knowledge regarding stormwater management in the US under climate change, identify design modifications to SCMs that have been explored, propose challenges that lie ahead, and provide a vision for the future. Although this article provides a US-centric perspective, it is known that similar performance challenges exist in international contexts.

Enhancing the resilience, or the ability of a system to continue to function as expected in the face of change (Gersonius et al. 2012), of SMS through adaptive approaches is an area of active research. In particular, nature-based solutions can partially mitigate projected increases in surface runoff and flooding caused by climate change (Waters et al. 2003; Gill et al. 2007; Zahmatkesh et al. 2015; Moore et al. 2016). As a result, the stormwater management community now considers green stormwater infrastructure, including bioretention, green roofs, rainwater harvesting systems, and grassed swales, to be an integral component of adaptation planning (Gaffin et al. 2012; Hettiarachchi et al. 2022). Batalini de Macedo et al. (2021) referred to this as second-generation low-impact development (LID-2G).

In response, researchers have begun to examine the impacts of climate change on SCM performance at the site and watershed scales. Examples of research approaches for simulating future climate scenarios include change factor methods (in which scaling factors are applied to historical rainfall patterns), development of new design storm depths or intensities, modification of intensity–duration–frequency (IDF) curves, rainfall disaggregation or downscaling techniques, and statistical models, often coupled with urbanization or development scenarios (Barah et al. 2021; Moore et al. 2016; Rosenberger et al. 2021; Semadeni-Davis et al. 2008; Tirpak et al. 2021; Wang et al. 2019; Zahmatkesh et al. 2014; Zhang et al. 2019). The performance of several SCMs has been modeled using climate change projections, including bioretention (Hathaway et al. 2014; Winston 2016; Tirpak et al. 2021), permeable pavement (Liu et al. 2015; Smolek 2016), green roofs and walls (Barriuso and Urbano 2021; Vanuytrecht et al. 2014), rainwater harvesting systems (Tavakol-Davani et al. 2016), constructed wetlands (Zhang et al. 2019), and retention ponds (Sharma et al. 2016). Although some studies found minimal effects on SCM function (e.g., Zahmatkesh et al. 2015), many studies reported diminished performance for SCMs designed using existing design criteria under future climate conditions (as discussed subsequently). Designing larger SMS or including other potential factors of safety may suffice for maintaining performance and may buffer against uncertain future climate conditions (Liu et al. 2015; Tirpak et al. 2021; Zhang et al. 2019); however, such modifications likely will result in increased costs and additional use of land for stormwater control.

Climate change impacts on SMS performance depend on several factors, including SCM type, design approach, drainage area characteristics, and associated treatment processes. For example, runoff volume reduction, peak flow mitigation, and water quality treatment provided by bioretention facilities all will be impacted by changes in climate. Temporary surface storage zones, which often are sized based on historic rainfall records, may be overwhelmed more frequently by forecasted larger, more intense rain events, resulting in more frequent untreated stormwater and occasionally wastewater flows (i.e., in combined sewer overflow watersheds) bypassing treatment (Olsson et al. 2009; Hathaway et al. 2014; Winston 2016; Alamdari et al. 2020). Similarly, prolonged dry periods between rain events coupled with increased air temperatures may stress plants and microbial communities that remove pollutants via uptake and microbially mediated processes, such as denitrification (Fowdar et al. 2021). Even successful runoff capture may result in management challenges; for example, increased runoff volumes retained following projected extreme events could lead to more localized groundwater mounding, which may impact adjacent infrastructure (Machusick et al. 2011).

In response to current and future shifts in climate, the stormwater management community has begun to evaluate strategies that will improve SCM resilience. These design alterations are to either the physical properties of SCMs (e.g., depth of ponding, the ratio of watershed area to SCM surface area, vegetation type, and so forth) or the hydrologic design criteria of SCMs (e.g., increased design storm size, designing based on recent storms of concern, and so forth). These responses are not mutually exclusive, and mitigation strategies are likely to employ both categories. These design changes also will impact water treatment, because it is linked inextricably to SCM hydrologic function.

The magnitude of changes to SCM design characteristics may depend on the severity of climate change for a given region. Locations at which these changes are projected to be greater may require more-intensive adaptations (e.g., larger storage volumes, deeper filters). For example, Hathaway et al. (2014) found that bioretention surface ponding depth in North Carolina would need to be increased by a factor of approximately 1.7–2.7 to limit overflow volume under climate change to that of the current climate. Cook et al. (2021) observed substantial ($\sim 30\%$–50%) decreases in runoff reduction for bioretention systems under climate change projections for Memphis, Tennessee, and for Pittsburgh. Although many locations may not require extreme design interventions, sizable design changes could be necessary for some locations depending on the desired level of service. Conversely, minimal deviations from current design practices may be sufficient in areas in which minimal changes are forecasted (Weathers et al. 2023; Winston 2016). Further complexity is added by site-specific conditions, which also may drive adaptations required for infiltration-based SCMs. For example, extensive design modifications may be required for SCMs installed over poorly draining soils, whereas existing designs installed atop rapidly draining native soils may still provide adequate treatment under future conditions. Furthermore, temperature-related variability in the performance of infiltration-based SCMs (i.e., higher recession rates in warmer months) has been observed in some regions (Ebrahimian et al. 2020), and can be leveraged for optimizing the SCM design as the climate warms (Ebrahimian et al. 2021). However, the infiltration dynamics may change in different regions depending on the severity of climate (temperature) change. Real-time control of SCMs, which may adapt the storage capacity, detention time, and peak outflow rate of SCMs based on forecasted weather, is another means to manage changing amounts of rainfall that are associated with climate change (Brasil et al. 2021; Persaud et al. 2019). However, real-time control of SCMs is not a silver bullet; there are limitations in the ability to adapt SCM performance using real-time control, because their original design specifications remain static.

The second category of adaptations is related to the design criteria utilized for SCMs. The stormwater management community lacks an organized, globally accepted approach to sizing and design criteria, leading to varying climate-based modification approaches across communities worldwide. Notably, efforts are underway to provide more standardized specifications and testing through the ASTM E64 Committee on SCMs, which may include climate-based modifications for different types of SCMs (ASTM 2022). Regardless, substantial and specific actions are being taken by designers to adapt to the effects of climate change (Table 1). These approaches vary, but examples include utilizing climate model projections of future conditions to update IDF curves, considering recent extreme events in modeling and design, and evaluating high-intensity events and the accompanying shift in rainfall intensities for the design event (Mailhot and Duchesne 2010).

Climate change poses a substantial threat to communities worldwide, leading to increased weather extremes that can overwhelm SMS. Stormwater drainage infrastructure lies at the front line of these impacts, but also is key to cities becoming (more) climate resilient. To achieve the desired level of service, modern and innovative design standards and techniques will be needed. In addition to utilizing increasingly available future climate projections to inform designs (such as the examples in Table 1), several additional factors and approaches that are now essential to incorporating climate change into stormwater management are as follows:

Currently, many approaches presented in the literature (i.e., Hathaway et al. 2014; Tirpak et al. 2021) and in Table 1 rely on design changes to maintain the same level of performance in the future as has been provided historically. For example, this has taken the form of maintaining the same frequency of overflow for bioretention, increasing the size of design storms based on future conditions, and so forth However, additional considerations should be made to determine whether historical design criteria can achieve the level of resiliency desired by communities. From this, critical philosophical questions arise that should guide stormwater management over the coming decades:

These are the questions that stormwater professionals will wrestle with in the coming decades as climate change and its effects are realized around the world.

The legacy of twentieth-century stormwater infrastructure largely has been one of inadequacy, because stormwater remains a leading cause of impairment for many US waters and nearly all urban or urban-adjacent waters (Walsh et al. 2005). Current and future stormwater professionals can create a different legacy for the 21st century and beyond. Climate change is no longer on the horizon—it has arrived and will continue to come ashore, overloading our infrastructure more and more frequently. However, the strategies and tools included here provide a guide to the profession for moving forward in the face of change that may last as long as careers. Like the communities that are served, stormwater professionals must adapt to climate change while it is happening.

No data, models, or code were generated or used during the study

This article was prepared by members of the American Society of Civil Engineers Urban Water Resources Research Council (UWRRC)’s Climate Change Subcommittee who collectively recognized the need to aggregate resources for stormwater professionals tackling the unique and varied challenges presented by climate change.