Rainfall interception by Santa Monica’s municipal urban forest

The ability of urban trees to intercept rainfall and reduce runoff has been described, but little work has been done to quantify the benefits. In this study, the amount of rainfall intercepted by the urban forest of Santa Monica was modeled. Model inputs included tree data taken from the City’s street tree inventory and an earlier study that included an intensive field inventory of a random sample of trees, hourly weather data for the year 1996 (a “typical” rainfall year), and a single-tree rainfall interception model. The annual rainfall intercepted by the public trees of Santa Monica was estimated at nearly 200,000 m³, which was valued at approximately $111,000 ($3.80/tree). The value includes two components: avoided stormwater treatment ($3.20/tree) and avoided flood control ($0.60/tree). Unsurprisingly, the largest benefits accrued to the largest trees and to the evergreen trees, since most rain falls in California during the winter. Management recommendations for increasing rainfall interception are presented.