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Abstract. Modelling the water transport along the soil–plant–atmosphere continuum is fundamental to estimating and predicting transpiration fluxes. A Finite-difference Ecosystem-scale Tree Crown Hydrodynamics model (FETCH3) for the water fluxes across the soil–plant–atmosphere continuum is presented here. The model combines the water transport pathways into one vertical dimension, and assumes that the water flow through the soil, roots, and above-ground xylem can be approximated as flow in porous media. This results in a system of three partial differential equations, resembling the Richardson–Richards equation, describing the transport of water through the plant system and with additional terms representing sinks and sources for the transfer of water from the soil to the roots and from the leaves to the atmosphere. The numerical scheme, developed in Python 3, was tested against exact analytical solutions for steady state and transient conditions using simplified but realistic model parameterizations. The model was also used to simulate a previously published case study, where observed transpiration rates were available, to evaluate model performance. With the same model setup as the published case study, FETCH3 results were in agreement with observations. Through a rigorous coupling of soil, root xylem, and stem xylem, FETCH3 can account for variable water capacitance, while conserving mass and the continuity of the water potential between these three layers. FETCH3 provides a ready-to-use open access numerical model for the simulation of water fluxes across the soil–plant–atmosphere continuum. 

Abstract Water smart cities are increasing their use of irrigation and misting to cope with extreme heat and drought. This is being enabled by widespread use of rainwater tanks, stormwater capture and storage systems, and recycled sewage wastewater to irrigate street trees as well as private and public green spaces. These alternative water resources provide new options for cities to better withstand and function under extreme summer heatwave conditions with little or no impact on drinking water supplies. Small‐scale approaches to evaporatively cool urban animals, vegetation habitat, and people are showing initial success. However, ongoing testing and modeling are needed to understand the impacts of scaling up these interventions and to evaluate their cost‐effectiveness. We describe current innovations in irrigation of Australian cities to help policy development in other countries and cities experiencing similar climates with episodic summer heatwaves.