Cities often rely on concrete drainage channels to handle urban rainwater, carrying it from the streets and impermeable areas to local rivers and ponds. This grey solution not only transports water but also pollution and does not resolve the core issue of impermeable surfaces. Trees and urban parks can provide significant pluvial flood mitigation along with other benefits. The soil and roots of trees improve groundwater infiltration, whilst their branches and leaves intercept rainfall and evapotranspire water back into the atmosphere. This green solution attenuates the intensity of pluvial flooding by slowing and storing water during intense rain events. Citizen scientists collected data on the absorption capacity of urban trees and green spaces. They measured soil characteristics in 36 locations and gathered over 520 samples in public parks in London, Birmingham and Paris. These metrics are being used to calibrate models of the infiltration capacity of soil and reduction in run-off to determine avoided urban flood risk.