Dr. Kevin Mueller and Dr. John Van Stan, both members of the Department of Biological, Geological, and Environmental Sciences (BGES), have been awarded $672,505 over three years for their project, “Modeling the mysterious flow of rainwater and nutrients through urban tree canopies: a laser-focused integration of hydrology and ecology.” 

Tree canopies have large surface areas that interact with rainfall to affect the quantity and quality of stormwater runoff in cities. For example, trees can redirect some rainfall back to the atmosphere via evaporation of water that gets ‘stuck’ on leaves or branches (known as interception), or into soils by funneling rainfall down their trunks (known as stemflow). These flow pathways can prevent rain from pouring directly onto pavement, overloading storm-sewers and carrying pollutants into rivers. 

The funded research will focus on ~30 tree species located in an arboretum near Cleveland, Ohio. The research team will use terrestrial laser scanning and other methods to measure varied characteristics of canopy form, like leaf waxiness, leaf and branch angles, bark roughness, and the surface area of leaves and branches. Hydrological measurements beneath each tree will quantify canopy interception (rainfall that doesn’t reach the ground), stemflow (rainfall draining down trunks with a greater chance of infiltration into soils), and throughfall (rainfall dripping through canopies that may ‘land’ on impervious surfaces and ‘run off’). The amount of nutrients in stemflow and throughfall will be monitored to inform how trees mediate the flow of airborne nutrient pollution into soils and stormwater systems. 

This work can help cities improve the selection of tree species to reduce stormwater runoff and other challenges related to rainwater management.