Investigations into the Coupled Human-Natural System Drivers of Watershed Function
In human-populated watersheds, hydrologic outcomes are the collective result of both human and natural drivers. Just as naturally occurring events occur at different spatial and temporal frequencies, human activities create unique environmental contexts that also influence the performance of these physical systems in myriad and significant ways. If global atmospheric circulation patterns are the primary cause of precipitation, it is land use and land cover decisions that partition it into runoff, soil moisture, recharge, and evaporation. Global trade of agricultural and other products creates significant flows of virtual water; cities cast rain shadows; natural river systems propagate pollution and water-borne diseases, and unsustainable irrigation practices deplete fossil groundwater supplies.
While most hydrologic research seeks to develop new and improved methods to understand and model how various natural climatological and geophysical properties vary in time and space in unpopulated watersheds, the emphasis of research at the SWRE lab is on populated watersheds, i.e. watersheds that are heavily impacted by human activity and infrastructure. Indeed, as the human population grows, urbanizes, and continues to colonize coastlines, the desire to more sustainably manage water and other natural resources requires the development of new insights into how people, infrastructure, and ecosystems functionally interact at a variety of scales.
Our research studying the coupled human-natural system drivers of watershed function makes use of physical, agent-based, and mediated modeling tools. We conduct interviews and participant observation, organize interactive workshops, and develop surveys, working directly with governmental, non-governmental, and community stakeholders. We have worked domestically in cities like Philadelphia, New York, and Camden but also abroad in countries as diverse as Haiti, Ethiopia, and Italy.
Engineering, Enhancing, and Restoring Urban Ecosystems through Ecohydrologic Research
With geomorphology and biology, hydrology constrains the stocks and fluxes of organic and inorganic materials and energy in natural systems and is one of the key determinants of terrestrial ecosystem function. In particular, the spatial and temporal characteristics of the soil moisture field plays a crucial role in biogeochemical cycling and all in physiological plant processes (e.g. growth and photosynthesis), which in turn determine evapotranspirative fluxes of moisture to the atmosphere, primary productivity, latent heat fluxes, nutrient dynamics, and a host of other ecologically significant processes. Because of the many functional interrelationships that exist between hydrology, and various biological, ecological, biogeochemical, and climate patterns and processes, water management is central to forging a new path towards climate-resilient sustainable development.
At SWRE, our interest is in studying hydrologic processes in functional urban ecosystems so that they can serve as references in the restoration, enhancement, and creation of new urban green spaces. Our goal is to translate scientific findings derived from ecological reference sites into the design of restored, enhanced, or newly created urban land and waterscapes. Most of our work has been in mid-Atlantic urban wetlands, forests, parks, and gardens.
Green Infrastructure Planning, Modeling, Monitoring, and Assessment
The US Environmental Protection Agency defines green infrastructure (GI) as “a cost-effective, resilient approach to managing wet weather impacts that provides many community benefits”, and over the past few years, many cities have begun dedicating significant resources to GI implementation, principally as a distributed means of stormwater management. In combined sewer districts, stormwater that is retained in rain gardens, bioretention facilities, permeable pavements, green roofs and constructed wetlands can help to reduce the frequency and volume of combined sewer discharges. In separately sewer-ed districts, GI systems can directly reduce the pollutant load that urban stormwater poses on receiving water bodies. But by greening urban watersheds, we are potentially accomplishing much more than stormwater management. Depending on where and how they are installed and maintained, GI systems can provide aesthetic improvements, enhance biodiversity and climate resilience, while creating new forms of recreation and employment. In this way, GI is critical in efforts to enhance urban ecosystem services.
With an extensive network of more than 30 field monitoring sites, the SWRE group has quantified the ability of green roofs to attenuate incident precipitation (Alfredo et al 2010, Abualfaraj et al 2018) and provide thermal buffering (Alvizuri et al 2017), compared in-situ surface infiltration rates of tree pits, green streets, permeable pavements, permeable playground surfaces, and urban parks (Alizadehtazi et al 2016), and compared the stormwater capture performance of an urban bioretention facility under both extreme and non-extreme precipitation conditions (Catalano de Sousa et al 2016). Along the way, the team has made important methodological contributions, for example regarding the suitability of classical equations for modeling urban evapotranspiration (DiGiovanni et al 2013) and urban soil heat flux (Smalls-Mantey et al 2013), stochastic precipitation generation (Basinger et al 2010), and model scale and resolution (Goldstein et al 2016). Such insights have helped us to more comprehensively simulate the potential watershed scale impacts of wide-scale implementation of urban GI systems. For example, we have simulated the stormwater capture potential of New York City’s urban yards (Mason and Montalto 2014), modeled the extent to which residential rainwater harvesting practices could reduce runoff and potable water consumption in four North American cities (Rostad et al 2016), and developed a modeling tool for comparing GI to more conventional approaches of CSO control (Montalto et al 2007).
SWRE been working with decision-makers in and around New York and Philadelphia to maximize the community value that can be derived from GI for several years. This work has involved a “thick” exploration of community needs and constraints relevant to GI planning in one south Philadelphia neighborhood (Travaline et al 2015), a comprehensive mapping of ecosystem services that could be enhanced through strategically designed GI systems in Camden, NJ (Zider et al 2017), the use of agent-based models to explore how community stakeholder preferences and actions could influence spatial patterns of GI buildout (Montalto et al 2012, Zidar et al 2017), and the development of new approaches for engaging community stakeholders in GI planning and goal setting (Montalto et al 2011, Aguayo et al 2013, Woerdeman et al 2017). Through its Green Infrastructure Living Laboratory project, SWRE has developed a cloud-based platform for ingesting both sensor data and observations made by the public using a web app to be used to characterize the performance of GI systems located in and around the University campus.
Urban Resilience Planning
Climate change is one of the defining issues of our generation, and cities urgently need to find ways to cut emissions, while adapting to increased frequency of extreme and unpredictable climatic events and continuing to develop cost-effective, and politically feasible ways of improving social and ecological conditions. The most recent IPCC reports emphasize the need to achieve “net zero” emissions globally by mid-century and decisions regarding the planning, design, and operation of urban infrastructure will be critical in achieving this goal.
In large part a result of the research conducted at SWRE, Drexel has been a core member of the Consortium for Climate Risks in the Urban Northeast (CCRUN), an NOAA-funded consortium of five universities that have been working together to evaluate and mitigate the risks that climate change poses on the urban northeast. Recently, Drexel was selected to host the North American Hub of the Urban Climate Change Research Network (UCCRN), an international consortium of both researchers and city leaders who are focusing explicitly on the impacts of climate change on cities.
SWRE research in this area seeks to define multifunctional infrastructure investments that will function regardless of what the future brings. We seek to help urban stakeholders to more cost-effectively accomplish their goals, in spite of, or perhaps even more effectively in the future. We see cities as the front line in urban resilience planning and conduct research in real communities to develop new and replicable forms of climate-smart urban design.