You definitely know if you live like us in Dubai : we live in very hot temperatures and are very exposed to the sun. Especially from May to September, when temperatures break records every year. This prolonged exposure to light is very aggressive for the most fragile acrylic paints (or poorly protected), and this is a subject that particularly affects us. When it comes to indoor paintings, there is no problem because the surfaces are not directly exposed to the sun. Ultimately, it is not the heat that is harmful for murals but the light rays.
The best solution to protect a wall is to apply a suitable varnish once the project is finished. Although, it is often very expensive, there are very good solutions to lengthen the life of a graffiti painted outdoors in a climate very exposed to light.