Urbanization and its impacts on water, energy, and carbon

Urbanization permanently alters ecosystems that humans depend on. Urban watersheds have increased runoff and flood risk, loss of green space, microclimate changes such as urban heat islands, and other impacts. Urban planning and watershed management focusing on the role of vegetation can help mitigate these negative impacts on urban watersheds – and the human communities that live in them.

urbanizationUrbanization often involves loss of natural wetlands and removal of vegetation. The permanent change in land cover and land use, including greater imperviousness of the land surface, dramatically disrupts water, energy, and carbon balances. SRS scientists and partners examined how future urbanization in the years 2050 and 2100 is expected to change water yield and ecosystem productivity across U.S. watersheds. 

Using the WaSSI model, the team found that urbanization usually leads to a loss of plants and trees, along with an increase in pavement and other permeable surfaces. These changes lead to less water retention and less water transpired to the air by trees, as well as more runoff. Ecosystem productivity – which represents food available to aquatic animals and other wildlife – also declines. Several factors determined the impacts of urbanization, according to the analysis: Impermeable surfaces, local precipitation (wet vs. dry climate), and previous vegetation characteristics (e.g., forests vs. grass). 

This research provides new evidence that helps explain common urban environmental issues such as urban heat islands, urban dry islands, and urban flooding. Impacts of urbanization are not created equal. Thus, urban planning and watershed management should fit local climatic and vegetation conditions. 

Pictured: Modeled impacts of urbanization on water balances in a watershed in Pennsylvania with the USFS WaSSI hydrological model. USDA Forest Service image.

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Contact: Ge Sun, Eastern Forest Environmental Threat Assessment Center, ge.sun@usda.gov.

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