The Köppen code for a Mediterranean climate with hot summers is Csa.
The first letter, C, identifies a temperate climate; s means dry summer; and a means hot summer. In the standard Köppen definition, the warmest month averages above 22°C. Csa climates typically have hot, dry summers and mild or cool, wetter winters, a pattern created by shifting subtropical high-pressure systems and winter storm tracks.
The Mediterranean Basin provides the classic examples, but Csa climates also occur in California, central Chile, parts of southwestern Australia, southern Africa, and areas around the Black and Caspian seas. The label “Mediterranean climate” can be broader than Csa because it may include Csb, the warm-summer subtype. Csb has dry summers too, but its warmest month stays below 22°C. Another common mistake is choosing Cfa: that code describes humid subtropical climates without the defining dry-summer pattern.