Cities and global hydrological models the next frontier

Global Hydrological Models (GHMs) are now being used to evaluate freshwater availability for water supply and estimate competition between sectors (municipal, agricultural, industrial water withdrawals, etc.) under the projected population increase and climate change. While becoming more complex and versatile GHMs are still fundamentally undervaluing cities. Over past decades, urban hydrological research has documented numerous changes to hydrological cycle beyond faster and flashier hydrographs. Cities alter rainfall patterns, create subsurface preferential pathways, so-called urban karst, can increase local recharge, to name a few. By using global datasets on water withdrawals, cities, permeability, and non-revenue water we show how current conceptualization of cities within GHMs could be improved to account for key urban complexities at scale. We identify regions where such improvement should be implemented and call for the creation of urban global hydrological modelling community, a community which will help to evaluate local model performance and creation of fundamental urban global datasets.