The climate where the casks are housed during maturation can be very important to both the flavour and strength of the whisky. The casks are wooden and poreous, during the summer they will expand and then they will contract during the winter, breathing if you will.
As whisky evaporates that space in the cask will be filled with air from the outside. It has been noted that casks matured near the sea will often take on salty, briny flavours. The strength is affected by heat. If the casks are matured somewhere relatively hot a higher loss in water will occur with a consequental gain in spirit strength. With damper and colder conditions more alcohol will be lost, lessening the alcoholic strength.