A novel dimension of the Barcelona project regarding the selection of the schools to be converted to Climate Shelters, is that it takes note of the urban (land cover), environmental (temperature, air pollution, greenery) and climatic (heat wave vulnerability) conditions in the city of Barcelona, as well as their spatial variations.
From an urban perspective, the above conditions are also linked to land cover, which for the case of the City of Barcelona is depicted in Figure 1  for the year 2018. An examination of Figure 1 shows that a major part of Barcelona falls in the class “Continuous urban fabric Sealing Layer SL>80%”. This class is assigned when urban structures and transport networks are dominating the surface area. In addition, more than 80% of the land surface is covered by impermeable features like buildings, roads and artificially surfaced areas. Non-linear areas of vegetation and bare soil are exceptional. Furthermore, this class includes residential buildings, public service and commercial/industrial buildings with their connected areas with their size being less than 25 ha, parking lots, concrete or asphalt surfaces, small squares, pedestrian zones, yards and urban greenery (parks and grass areas) of size less than 25 ha and accounting to maximum 20% of the polygon area.
The extended coverage of the city with impermeable materials results in high values of land surface and air temperatures, the latter due sensible heat transfer from the ground to the air above. Areas like these are more vulnerable during summer months and particularly in the event of heat waves.
Figure 1. Land cover map of the City of Barcelona for the year 2018 (dark red refers to areas with continuous urban fabric Sealing Layer>80%, whereas purple refers to industrial, commercial, public, military and private units).
Land cover needs to be correlated to the spatial distribution of temperature so as to recognize the impact of urban form and functions to the state of the thermal environment, especially in the event of heat waves. Figure 2 presents the spatial distribution of temperature in Barcelona during the heat wave of 2015 .
Further analysis is considered necessary so as to assess the city’s vulnerability to high temperatures  in conjunction with such risk parameters as: population over 75 years old, energy insulation of buildings and amount of greenery in the city. vegetation. A respective map is presented in Figure 3.
Figure 2. Spatial distribution of air temperature during the heat wave of 2015. Areas with higher temperatures are associated with lower % of urban green.
Figure 3. Spatial vulnerability to high temperatures associated to heat waves.
To further explore the state of the urban environment, it is important to record the levels of photochemical air pollutants and correlate them to air temperature. Figure 4 provides the exposure levels of the population to the average annual concentration of NO2 for the year 2019 .
Figure 4. Exposure levels of the population to the average annual concentration of NO2 for the year 2019. Areas in orange and red exceed the EU limit value/WHO guideline of 40 μg/m3 (orange from 40-50 and red from 50-60 μg/m3).
Finally, urban greenery - especially street level trees -is beneficial for cooling (through evapotranspiration) and for shading. Figure 5 refers to Copernicus street layers trees product for Barcelona .
Figure 5. Street layer trees in Barcelona (2018).