Why does it look like a wet road in the distance when the weather is hot?

On the hot road, air layers with different densities are formed, and the closer to the ground, the smaller the refractive index of light. When light is emitted from an optically dense medium to an optically hydrophobic medium, the light will be far away from the normal, that is, the incident angle will gradually increase, and total reflection will occur when it reaches the critical angle. At this time, from a distance, the ground is like a mirror, which can reflect the distant scenery. Our habitual intuition tells us that there should be water there, but there isn't. This phenomenon often occurs in the desert and is called a mirage.