1.5. Methods
There are two main ways to study the urban climate: measuring what is happening with measurement networks or using models to simulate the climate. From an instrumental point of view, the urban environment has several disadvantages: i) it is necessary to obtain multiple meteorological measurements which require devices which are sometimes very expensive; ii) as the city is a heterogeneous environment, but since it is not possible to install the devices everywhere, we must sample the most interesting sites; iii) the vertical dimension must be taken into account, that is to say the links between the ground and air in the street (the urban canopy), and the links between the street and the air layers above the roofs (Figure 15).
While the measurements are long and expensive to perform, simulation by numerical models with physical bases offers an alternative solution. Depending on the goal, it is possible to use more or less sophisticated microclimate models or meso-scale models. Models are very useful because, after being scientifically validated, they can inform us about the main processes that are at the origin of the urban climate and it is possible to use them to test remediation hypotheses with different scenarios.