climate models show that while some regions should expect an increase in precipitation, such as in the tropics and higher latitudes, other areas are expected to see a decrease, such as in the subtropics. this will ultimately cause a latitudinal variation in water distribution. the areas receiving more precipitation are also expected to receive this increase during their winter and actually become drier during their summer, creating even more of a variation of precipitation distribution. naturally, the distribution of precipitation across the planet is very uneven, causing constant variations in water availability in respective locations.