A new study from the University of Nottingham and other international partners has tested the accuracy of global water models and whether they agree with each other.
In a study recently published in Nature Water, the University of Nottingham has worked together with an international team, led by the University of Potsdam, to test the extent to which global water models agree with each other and with observed data taken from rivers and groundwater sources around the world.
Using a new approach, the researchers show in which climate regions of the world the models agree and where they differ.
Global water models are essential tools for understanding the water cycle, including to help understand the impacts of climate change.
Our society is experiencing many of these impacts through changes in water extremes such as increasing droughts and floods, which pose growing threats to people and ecosystems.
But there are also changes in general water availability, for example soil moisture, which is relevant for agriculture, or groundwater recharge, which is important for the sustainable use of groundwater.
Inconsistencies between the results of different global water models make such model-based conclusions uncertain. These differences have not yet been fully quantified and previous evaluation approaches have provided limited information on how the models could be improved.
The study is the first to use large-scale relationships between climatic and hydrological variables to reveal differences between models and in comparison to observational data.
Relationships between climatic and hydrological variables – so-called functional relationships – provide an overview of how the global water cycle functions.
Looking at such relationships in the models and comparing these to what we see in the real environment, the research team was able to answer questions like how much groundwater depends on precipitation. Answers to such questions are enormously important but are often missing for large areas of the world.
Professor Simon Gosling, co-author of the study, explains: "Global water models are incredibly useful tools for helping understand inequities in patterns of global water supply, and the effects of extremes like river flooding on society.
"It is important, therefore, that we know how well the models do their job, because the quality of the models mirrors the scientific community's understanding of how global hydrology works. In this study we take a more holistic view than done in past studies, by looking at different parts of the hydrological cycle that interact with each other, and then seeing whether these interactions in the models are the same as what we see in the real world.
Our results show that there are opportunities to enhance scientific understanding of processes like energy balances and groundwater recharge, especially in dry and/or cold regions of the world."
