Science question 2
Forecast of Storms, Urban heat islands and cool areas, air quality, in cities
New scientific issues are raising for atmospheric models when dealing with resolution of 100m in urban areas. While urban canopy models are now usually used in most of kilometric NWP models, they often use the hypothesis of the street canyon. Is this hypothesis still valid at high resolution? How to take into account the urban vegetation in interaction with buildings? How to describe the city characteristics in order to be able to simulate the variability of the wind field and UHI within a neighborhood?
Buildings typology in each urban block (red: attached buildings, orange: isolated building, black: high-rise building, dark green: continuous houses, light green: isolated houses). Zoom over Paris and inner suburbs.
Fine-scale city indicators (building fraction, building height, Local Climate Zone, building type, etc…) are available for modelers at the urban block scale for the whole Paris agglomeration.
While the above questions are valid all year, some specific issues appear in summer. One is on the evaluation of the anthropogenic heat fluxes, especially those due to air-conditioning, on the UHI. Another one is how the effects on thunderstorms amplification or splitting due to the urban surface energy balance could be included for a better thunderstorm forecast?
Finally, interaction between Air Quality and urban micro-climate is still an open question. Cities are of course locations of high pollutant emissions, and this is correctly considered in all AQ modeling systems, but the specificities of the urban boundary layer (e.g. mixed boundary layer even at night) on the mixing of the pollutants, and their impacts on concentrations, need to be further studied. Artificial Intelligence could also be explored in order to allow very-high resolution of Air Quality forecasts, not only urban micro-climate forecasts.
Several cases of heavy thunderstorms and heat waves with strong UHI have been documented by the operational network of Meteo-France around Paris. They will be proposed as test cases to the participants. For example, during the second part of the night of the 9th to the 10th of July 2017, stationary storms form above Paris and inner suburbs, and lead to precipitation amounts and hail of up to 98mm inside Paris. 4 recent cases of heat wave (with daytime temperature larger then 38°C in Paris) and strong night-time UHI.
Nighttime UHI typical of a summertime episode with calm winds. The simulations were done with the MesoNH atmospheric model at 250m of resolution.