What is astronomical tide?

Astronomical tide is a normal astronomical tide phenomenon with a period of 18.6 years, which can be predicted several years before its arrival.

Generally speaking, astronomical tide will not bring disaster. But in some specific cases, it will constitute a flood. In the first case, if there is a typhoon or a typhoon is about to land during the astronomical tide, a storm surge will break out.

Storm surge is a kind of marine disaster that occurs along the coast. It is a phenomenon that the water level rises and falls sharply due to strong weather systems such as strong winds or sudden changes in air pressure, which usually causes certain harm to coastal areas. Storm surge disaster ranks first in marine disasters, and most of the major coastal disasters caused by strong storms in the world are caused by storm surge. Therefore, its power cannot be underestimated.

In the second case, the river water level is low, the upstream range of tide is enlarged, and the degree of salt damage is aggravated, which leads to the emergence of salt tide.

Salt tide is a natural phenomenon, which is caused by the attraction of the sun and the moon to the surface seawater, also known as the upper reaches of salt tide and salt water intrusion. When the freshwater river is short of water, the seawater will flow backwards, and the mixing of salt and freshwater will make the upstream water salty and form a salty tide. Salt tide mostly occurs in winter or dry season, and it appears at the intersection of rivers and oceans between June 10 and March of the following year, such as around the Yangtze River Delta and Pearl River Delta.

If the weather changes or ebbs, it will affect the salty tide. Especially in the astronomical tide, the salt tide is more serious. In addition, the process of sea level rise caused by global warming gradually increases the salt tide, but it will change obviously in the long run.