The protests are part of a global initiative that envisages 3,167 rallies in more than 100 countries worldwide from 20 to 27 September.
The Fridays For Future is an international movement which describes itself as a peaceful and quiet striking organisation, and it follows Swedish environmental activist Greta Thunberg's actions.
The protests in Zagreb, Osijek, Rijeka and Split begin at 1800 hrs on 20 September.