The stormwater retention benefits of urban trees and forests

The use of urban tree canopies as strategies to mitigate stormwater runoff is limited in part by a lack of empirically observed data. This thesis quantifies soil infiltration capacity in 21 forest patches in Baltimore, Maryland, and reports results from a meta-analysis on urban tree transpiration. Results show that the degree to which soil infiltration and tree transpiration functions reduce stormwater runoff depends on soil physical properties, tree characteristics, and management drivers. Yet, results conservatively estimate that Baltimore forest patch soils are capable of infiltrating ~68% of rainfall. In addition, urban trees transpire ~1.7 mm of water per day in the growing season or ~0.8 mm of water per day on an annual basis, an amount of water that equals approximately 26% of the annual rainfall in the Baltimore region. Thus, urban trees and forests impact urban hydrology and are an important component of stormwater green infrastructure in built environments