Uncertainties in modelling global groundwater availability

As global water demand is projected to increase, it remains unclear how and where this demand will be met, or whether it will create new water-crisis hotspots. Projections of meteorological and hydrological droughts already suggest the emergence of new zero-day events. Yet groundwater, a vital buffer for meeting water needs and, at times, the only available freshwater resource, remains underrepresented in current assessments and global models. Groundwater faces substantial threats from overextraction, changes in recharge, and salinization caused by sea-level rise. Unfortunately, models that account for groundwater face significant uncertainties in simulating water table depth, interactions with surface waters, groundwater withdrawals, and groundwater recharge, and are challenging to evaluate. At the same time, these models are not yet capable of simulating water quality processes that may increase water scarcity and are only beginning to represent megacities. In this talk, I will address current uncertainties in global water modeling, examine the implications for water scarcity assessments and risk projections, and outline ideas for further model improvements. Specifically, I will highlight how community approaches to developing a groundwater sector within a model intercomparison project can enhance models and datasets, resulting in improved predictions of future water scarcity hotspots.