Articles | Volume 18, issue 21
https://doi.org/10.5194/gmd-18-8129-2025
https://doi.org/10.5194/gmd-18-8129-2025
Development and technical paper
 | 
03 Nov 2025
Development and technical paper |  | 03 Nov 2025

Implementation of water tracers in the Met Office Unified Model

Alison J. McLaren, Louise C. Sime, Simon Wilson, Jeff Ridley, Qinggang Gao, Merve Gorguner, Giorgia Line, Martin Werner, and Paul Valdes

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Cited articles

Allan, R. P., Barlow, M., Byrne, M. P., Cherchi, A., Douville, H., Fowler, H. J., Gan, T. Y., Pendergrass, A. G., Rosenfeld, D., Swann, A. L., Wilcox, L. J., and Zolina, O.: Advances in understanding large-scale responses of the water cycle to climate change, Ann. NY Acad. Sci., 1472, 49–75, https://doi.org/10.1111/nyas.14337, 2020. 
Best, M. J., Pryor, M., Clark, D. B., Rooney, G. G., Essery, R. L. H., Ménard, C. B., Edwards, J. M., Hendry, M. A., Porson, A., Gedney, N., Mercado, L. M., Sitch, S., Blyth, E., Boucher, O., Cox, P. M., Grimmond, C. S. B., and Harding, R. J.: The Joint UK Land Environment Simulator (JULES), model description – Part 1: Energy and water fluxes, Geosci. Model Dev., 4, 677–699, https://doi.org/10.5194/gmd-4-677-2011, 2011. 
Bosilovich, M. G. and Schubert, S. D.: Water Vapor Tracers as Diagnostics of the Regional Hydrologic Cycle, J. Hydrometeor., 3, 149–165, https://doi.org/10.1175/1525-7541(2002)003<0149:WVTADO>2.0.CO;2, 2002. 
Brown, A., Milton, S., Cullen, M., Golding, B., Mitchell, J., and Shelly, A.: Unified modeling and prediction of weather and climate: A 25 year journey, B. Am. Meteorol. Soc., 93, 1865–1877, https://doi.org/10.1175/BAMS-D-12-00018.1, 2012. 
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Short summary
We describe a new development in a state-of-the-art computer atmosphere model, which follows the movement of the model’s water. This provides an efficient way to track all the model's rain and snow back to the average location of the evaporative source, as shown in a present-day simulation. The new scheme can be used in simulations of the future to predict how sources of regional rain or snowfall might change owing to human actions, providing useful information for water management purposes.
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