In these times of scientific controversy on the issue of scales in hydrology, the IAHS Ultimate Frisbee tournament held during the 2015 IUGG General Assembly in Prague was expected to shed new light on this debate, by pitching downscalers against upscalers. Twenty players took part in the match on the field of the Vyšehrad close to the Congress Centre.

There was no observation round in this match and the upscalers quickly took the advantage after a few minutes. Their very detailed representation of the field thanks to a 10 cm resolution LiDAR data and to drone airborne measurements was very helpful to identify the best trajectories by applying least-energy principles. In contrast, the downscalers started with a large 10x10 km² scale and it took some time for them to adapt to the actual limits of the field and to find the best pathways to score. After trying a few statistical approaches, they opted for a deterministic one and managed to come back to 4 goals to 5. This was the time the upscalers chose to define efficient adaptation strategies, which resulted in five new successive goals. The golden Frisbee did not change the outcome of the match and the upscalers won.

After the match, the downscalers complained that they did not have recent enough data to cope with extreme situations. A more detailed analysis of the statistical parameters of the match showed that the team of upscalers was in fact a mix of upscalers and downscalers, and that the variety of experiences and points of view within the team strongly contributed to finding efficient solutions. This is a matter for thought before the next Ultimate Frisbee game planned in two years’ time in South Africa at the next IUGG Assembly.      

The participants of the Ultimate Frisbee game. The downscalers team: G. di Baldassare, A. Castellarin, J. Fabre, C. Furusho, S. Grimaldi, P. Hublart, F. Raynaud, A. Viglione, and M. Zappa. The upscalers team: H. Aksoy, M. Courbariaux, R. A. Montero, F. Neugirg, I. Pechlivanidis, C. Perrin, P. Pilon, D. Ruelland, A. Rücker, and G. Thirel.