What happens to salinity in a warm area with a lot of evaporation?
Salinity of a body of water will increase with evaporation, because the salts do not evaporate.
If a river supplies water to that body of water, than salinity might reach high values without the body of water drying completely. An good example would be the Dead Sea, witch has high salinity as the Jordan River constantly supplies it water and a little amount of salt. The water then evaporates in the desert heat while the salt accumulates in the sea.
Otherwise, without a river, a lake or sea will slowly shrink as it evaporate with its salinity increasing until it dries out totally leaving a salt lake behind. An example of that is the salt lake in the Death Valley.
Salinity is a measure of how salty water is. Ocean water is more salty in some places than in others. The answer is yes, places where rivers pour fresh water into the ocean have low salinity because fresh water is normally cold and in warm areas, ocean water evaporates quicker. When this happens, salt is left behind and the ocean water has a higher salinity.
Because Water vapor is why the air is warm More specifically the Evaporation/precipitation cycle puts heat into the air via water vapor carrying heat from the surface of the earth into the air If the Surface is hotter then more evaporation happens and in turn more heat gets into the air with the associated humidity