Because Earth has topography, mountains, hills and valleys and canyons. It might LOOK flat to you, but often there is slight "tilt" to the ground If you drive from o from the greater Oklahoma city area to the Oklahoma panhandle, your ears will probably pop several times because your really are going up to higher elevation, 500 feet or more. This is especially true if you do it from New Orleans, which is AT seal level, to the Oklahoma panhandle. . That change is of about 3500 feet or more in elevation. ( sorry, but I don't "think" in metric units). Air pressure decreases as you go up in altitude... May mother knew when we crossed the 100th meridian in a plane. and eventually i could feel the change too..
Earth has topography. That's why w liquid water flows downhill.. Storm surges are REAL. Don't kid yourself. Flash floods and storm surges Do a LOT of damage..A LOT of New Orleans is sinking back into the swamp AND sea level IS rising, slowly.