Paris 2024 Olympics Project results on urban heat modelling: intercomparison and application to the marathon event

The Paris 2024 Olympics Research Demonstration Project, endorsed by the World Weather Research Programme of WMO, aimed to make progress on future fine-scale weather forecasting systems in cities. The project brought together more than 20 national meteorological centres and laboratories from 10 countries.

During the Olympic and Paralympic summer, simulations from 7 hectometric numerical models were conducted daily by the partners. Comparisons were made with weather stations inside and outside the city. The results demonstrated the capacity of the models to reproduce urban effects, but also revealed large variability among models, particularly regarding the extent of the urban heat plume at night. This opens up new scientific questions, which are explored in depth using the crowdsourced netatmo observations, in order to assess the role of the various physical processes in play, such as the competition between hot air advection and local cooling in the suburbs.

A decision-making procedure was also established regarding whether or not to hold the Paris 2024 “Marathon for All” in hot weather situations. Throughout the summer of 2022, 100m MesoNH model simulations were conducted over Paris and its inner suburbs, extending to Versailles. Analysis of these simulations by expert forecasters from Météo-France Sports led to proposed scenarios assessing the heat stress conditions runners would face along the marathon route, based on their running speeds. The Paris 2024 marathon organisers were able to take this meteorological information into account when planning the event. A 100m MesoNH simulation was used specifically on the day of the Marathon for All to refine the forecasts of race conditions, and to adapt the safety and assistance arrangements for runners as best possible. This study shows the value of 100-m resolution models for targeted forecasting applications.