Trees impact surface stormwater runoff, soil moisture, streamflow, water quality, and air temperatures by intercepting precipitation (rain and snow), enhancing soil water infiltration, shading surfaces, and evapotranspiring water. These impacts affect human health and well-being. Many of these tree impacts remain to be more accurately quantified and valued, particularly related to water quality aspects such as mass (e.g., sediments), chemical (e.g., nutrients, metals, pesticides), biological (e.g., pathogens, microbes), and thermal loads. Urban trees can help mitigate many of the negative hydrologic effects created by the relatively large amount of impervious surfaces in cities. Urban tree impacts are generally positive but can create negative outcomes if improperly managed (e.g., leaves or branches clogging drains or streams). Although more and better valuation of tree impacts is needed, studies to date value tree effects on reducing runoff into water bodies in the range of millions of dollars per year at the city or watershed scale.
Nowak, D. J., Coville, R., Endreny, T., Abdi, R., & Van Stan, J. T. (2020). Valuing urban tree impacts on precipitation partitioning. In Precipitation Partitioning by Vegetation: A Global Synthesis (pp. 252–267). Springer International Publishing. https://doi.org/10.1007/978-3-030-29702-2_15