Trees in bioswales reduce runoff and discharge and return stored water to the atmosphere. Transpiration from trees in bioswales at The Morton Arboretum parking lot in Illinois accounted for 46-72% of the lot’s total water output.
Scharenbroch, Bryant C., Justin Morgenroth, and Brian Maule. (2015). Tree Species Suitability to Bioswales and Impact on the Urban Water Budget. Journal of Environmental Quality.