In the heart of bustling cities, where concrete jungles have replaced natural landscapes, a subtle yet significant shift is occurring in the way water and energy interact. A recent study published in the journal ‘Water Resources Research’ (translated from English as ‘Water Resources Research’) sheds light on how urban environments can be managed to better harness these interactions, with potential benefits for the energy sector.
At the forefront of this research is G. Aaron Alexander, a civil and environmental engineering professor at the University of Wisconsin-Madison. Alexander and his team have developed a new model that accounts for the complex ways water and energy move through urban landscapes. Their work, titled “Urban Ecohydrology: Accounting for Sub-Grid Lateral Water and Energy Transfers in a Land Surface Model,” introduces a modified version of the widely used Noah-MP land surface model, dubbed Noah-MP for Heterogenous Urban Environments (Noah-MP HUE).
Traditional models often overlook the intricate ways water and energy transfer across different urban surfaces. For instance, rainwater falling on rooftops or sidewalks can be redirected to lawns or pervious pavement, while trees can transpire water from branches overhanging impervious surfaces, with roots drawing water from nearby yards. These processes, though seemingly small, can have a significant impact on urban water and energy budgets.
“Even small percentages of sub-grid water transfer can reduce runoff and enhance evapotranspiration and deep drainage,” Alexander explains. This means that urban management practices, such as expanding tree canopies over pavement or disconnecting downspouts to direct water onto surrounding vegetation, can have a tangible effect on how water and energy are distributed in cities.
The implications for the energy sector are particularly noteworthy. By enhancing lateral water transfers and water storage through green infrastructure, cities can potentially alter land surface fluxes and atmospheric processes. This could lead to more efficient energy use and reduced demand for cooling, as latent heat is increased and sensible heat is reduced.
The study examined four scenarios: Urban Tree Expansion, Urban Tree Shift, Downspout Disconnection, and Permeable Pavement. Each scenario demonstrated how small changes in water management can lead to significant shifts in surface water and energy balances. For example, event-scale runoff reduction was found to depend on storm depth, rainfall intensity, and antecedent soil moisture, highlighting the importance of fine-scale heterogeneity on larger scale surface processes.
As cities continue to grow and urbanization becomes an increasingly global phenomenon, understanding and managing these ecohydrologic interfaces will be crucial. Alexander’s work opens a pathway to directly integrate green infrastructure practices into regional climate simulations, paving the way for more sustainable and energy-efficient urban environments.
The research underscores the importance of considering the fine-scale heterogeneity of urban landscapes in larger scale models. By doing so, urban planners and policymakers can make more informed decisions about how to manage water and energy in cities, ultimately leading to more resilient and sustainable urban environments.
This study, published in ‘Water Resources Research’, marks a significant step forward in the field of urban ecohydrology. As cities continue to evolve, so too will the need for innovative solutions that harness the natural processes occurring within them. Alexander’s work provides a compelling example of how science can inform practice, shaping the future of urban water and energy management.