Because the typhoon brings water vapor from the sea, and then it goes deep into the high altitude and becomes cold when it becomes water. Instead of directly rolling the salty water from the sea into the air, and then landing inland. This is why the rain in the sky after a typhoon is fresh water.
Typhoons are wind-driven and may stir up waves and form whirlpools in the sea. But in terms of its gravity, it is difficult to roll seawater inland over long distances. Therefore, in coastal areas, if they are hit by a typhoon, the waste at the coastal entrance will be particularly large. In this case, seawater may enter the city. In this case, the water will be salty.
But the fresh water in the sky cannot be salty. Those who have studied physics should be able to understand this. Rainfall itself occurs when cold air encounters water vapor and condenses into raindrops that fall from the sky. What the typhoon takes away is a layer of water vapor that evaporates on the sea.
The generation of water vapor may be due to the fact that the weather was too hot at that time and a layer of water vapor was produced by the evaporation of water on the sea surface. Basically, typhoons come from the sea, and it is unlikely that typhoons will automatically occur inland. After all, the inland terrain is not that broad, which caused certain obstacles to his journey.
So it is basically a typhoon formed by a tropical cyclone at sea under the influence of temperature. This year our country was hit by a typhoon. In the hot summer, a huge typhoon came from the sea and hit many cities along the coast.
It caused urban flooding and caused heavy losses. However, this is a natural factor that we cannot predict and estimate. What we have to do is to try our best to improve the urban drainage system and make preparations in advance.