The water takes more energy to heat up and cool. That’s why it’s often cooler near bodies of water, especially large ones, as they take more time to change temperature.

Normal “land” take a lot less energy, but there is still some heat and cold being kept that takes more time to change.

Deserts have nothing to keep the cold or the heat, so as soon as the sun is gone it’s far below zero, and as soon as the sun shows up it fires back up to very warm temps. Desert plants mostly survive by barely needing water.