Istanbul does not sit firmly in a warm mediterranean climate regime (Köppen Csa) even if it is still categorized as such in various sources, not neatly according to climatic attributes of Istanbul - and that does not include any micro-climatic condition because of its geography, such as the Bosphorus Strait as an example. Furthermore the summer while being the driest season, receives substantial rainfall, but is not very dry or extremely dry, as it is the criteria for a mediterranean climate.  Istanbul does not have a "dry season" with a total absence or near absence of rain during summer. The categorization of Istanbul as a warm mediterranean climate regime (Köppen Csa), is questionable and likely obsolete, and not due to "climate change". 

 An important fact is that the Köppen system is based on the concept that native vegetation is the best expression of climate. Thus, climate zone boundaries have been selected with vegetation distribution in mind. But Istanbul’s natural vegetation definitely does not fit the warm mediterranean climate regime (Köppen Csa) unlike Athens, Rome or Los Angeles whose mediterranean vegetation does correspondent with their warm mediterranean climate (Köppen Csa). Istanbul’s  dominant biome is the humid temperate broadleaf and mixed forest and constitute the Balkan mixed forests which belongs to the European-Siberian ecoregion of the Palearctic ecozone. The vegetation of Istanbul like the whole Turkish Black Sea and northern Marmara Sea coasts correspondents to the oceanic (Köppen Cfb) and humid subtropical (Köppen Cfa) climate regimes even if Istanbul’s climate is not categorized as such.  The mediterranean maquis shrubland vegetation is predominant only on the Princes' Islands just south of the Asian side of Istanbul; and palm trees for example which are not native to Istanbul and Turkish Black Sea and northern Marmara Sea coasts, are not able to grow to their natural height and thrive because Istanbul’s winters are too cold for them and stay miniscule and often die and are replaced by new ones.