Impacts of Nature-Based Solutions on Hydrology and Extreme Heat within Coupled Land-Atmospheric Simulations
Image credit: AGUAbstract
Urbanization substantially modifies both surface water and energy cycles. Paved urban surfaces produce more runoff, trap more heat, and lower evapotranspiration compared to natural ecosystems. In addition, increases in extreme rainfall and heat generated by climate change are amplified in urban areas due to feedbacks between urban heat islands and precipitation processes, which can exacerbate hydrologic impacts like flooding. In response, many cities are implementing urban resiliency plans that feature nature-based solutions or green infrastructure, which reduce the hydrologic impacts of urban spaces by more closely mirroring processes of natural watersheds. These plans also promise to reduce urban heat through adding tree canopy which shade pavements and enhance evaporative cooling. While these plans may provide potential benefits with respect to urban heat and climate feedbacks, these benefits have yet to be explored rigorously at scales actionable to city decision makers. In this project, we examine the city-scale impacts of widespread adoption of nature-based solutions on season long hydrologic and energy balances, rainfall changes, and extreme heat. We employ Noah-MP for Heterogenous Urban Environments (HUE), a new land surface model capable of resolving fine-scale hydrologic processes and heterogeneity in urban spaces, in multi-year regional climate simulations centered on Milwaukee, Wisconsin. Through multiple plausible greening scenarios, we find that runoff reduction is strongly tied to the amount of greening that occurs at city-scale, although partitioning of runoff reduction between evapotranspiration and deep drainage varies both year-to-year and by type of greening solution. We also find reductions in seasonal rainfall totals tied to greening which helps drive runoff reductions. During extreme heat events, nature-based solutions help reduce air temperatures via enhanced evapotranspirative cooling, but increases in humidity that coincide may decrease these benefits due to enhanced human health impacts and discomfort. Our results highlight that widespread adoption of nature-based solutions changes not only urban ecohydrology but also hydrometeorology. Future work should explore how hydrometeorological effects may vary across different climatological settings.
