Zhengzhou was hit by rainstorm and flood. While Chinese people are eager to help, they also have a lot of comments: what about the "sponge city" with a cost of 50 billion yuan and the flood control project? It was also compared with the flood disaster in Germany a week ago. Is Zhengzhou able to escape?

Professor J ü rgen Jensen, a flood expert at Siegen University in Germany, gave a clear answer when China officially announced that the maximum hourly rainfall in Zhengzhou reached 201.9 mm“ The rainfall is too heavy and the intensity is too high. I can't imagine. This is not just monsoon rainfall. It can't cause such a large amount of rainfall with the tap on all the time. Basically, there is an uninterrupted water curtain in the sky. No city in the world has a drainage system that can cope with such a situation. "

The picture shows Yan Sen, a flood expert at Siegen University in Germany

Speaking of "sponge city" and flood control system, Dr. JRG Rechenberg, an expert on precipitation and surface problems of the German Federal Ministry of environment, said in an interview with Deutsche Welle, "there is no doubt that the rainfall in Zhengzhou is huge, and it is easy to reach the upper limit of urban drainage facilities."

From 20:00 on July 19 to 20:00 on July 20, the daily rainfall in Zhengzhou reached 552.5mm. In Germany, the largest rainstorm in 75 years with meteorological records occurred from the 14th to the 15th earlier. The 24-hour precipitation in Cologne was 154mm. German Chancellor Angela Merkel described the disaster as "no German word can describe", while the Henan water resources department said the heavy rainfall was "once in more than 5000 years".

The picture shows Henan Province affected by rainstorm.

Yan Sen, a flood expert, said that if the rainfall data officially released by China is true, from the data of the peak rainfall, the level of the rainstorm in Zhengzhou, Henan Province is indeed much higher than that in Germany last week. The main factor causing flood disaster is a large amount of rainfall in a short time.

Generally speaking, if the rainfall in urban areas of Germany exceeds 40mm in one hour or 60mm in six hours, the highest level flood alarm will be triggered. According to the observation results from 16:00 to 17:00 on July 20 released by Zhengzhou meteorological observation station, the hourly rainfall per square meter reached 201.9 mm at that time, which is five times the highest warning value in Germany. It is said that this has broken through the historical extreme value of the hour rainfall in Chinese mainland.

Dr. leshing Berg, an expert on precipitation and surface problems of the Federal Ministry of environment of Germany, believes that it is difficult to say how much precipitation a city will face the threat of catastrophic floods. This is because it is related to the geographical location, geomorphic form, height drop, ground tightness and other indicators of relevant areas. All these determine the total amount of precipitation that can be handled per square meter per hour in an area.

He said that the violent rain and flood disaster in Germany a week ago is not much comparable to the current flood disaster in Henan, China. In Germany, the areas most affected by heavy rainfall are mountain streams or potholes, and there is no possibility of plane expansion of rainwater. The sealing degree of German ground is also completely different from that of Zhengzhou, a big city with a population of more than 12 million.

As of yesterday, the heavy rainfall and flood disaster affecting Europe had killed at least 206 people, including 174 in Germany, hundreds missing and 32 in Belgium. As of 12:00 on July 23, floods and secondary disasters caused by rainstorms in Zhengzhou had killed 51 people and caused direct economic losses of 65.5 billion yuan.

After the flood is before the flood. After the disaster, what needs to be done is to prepare for the next disaster. Professor Yan Sen said that it is a fact that heavy rainfall will often lead to irreversible climate change. The simple truth behind it is that the higher the air temperature, the stronger its water storage capacity. The more water in the air, the greater the probability of rainstorm. All these show what challenges climate extremes will bring to us. Especially for urban planners, it is more important to reserve more buffer zones in advance and reduce the sealing area - such as asphalt roads and large buildings, which can not absorb water.

Similarly, it has to be said that when there is super large-scale rainfall like Zhengzhou, even the protective measures designed by the "sponge city" may not be able to stop the occurrence of flood disasters. German expert leshing Berg pointed out that better drainage planning can at least reduce the level of disasters caused by such extreme rainfall. In the future, in order to prevent similar catastrophic scenes from happening again, or at least reduce the harm caused by disasters.

Therefore, leshing Berg believes that more attention should be paid to the construction of flood control buffer zone, including natural flood discharge area and man-made aboveground and underground flood discharge and storage pipeline system.