Eight meters in 45 minutes, “difficult to plan” … What is a “ray flood”, responsible for at least 80 dead in Texas?

The “sudden floods” have left at least 80 people since Friday, July 4 in the United States, in an area in Texas, sometimes called “Alley Flash Flaod”, “The alley of sudden floods.”

Despite the alerts issued by weather services on Thursday, the intensity of the rains and the speed of the increase of the waters at the night that followed and the devastation in the region.

The Governor of Texas, Greg Abbott, warned that the region was still under the threat of sudden floods until Monday night according to meteorological services.

Extremely fast increase in waters

“We didn’t know that this flood was going to arrive,” said Ker Rob Kelly County Judge, quoted by ABCNews. In fact, these floods took local authorities by surprise.

In question, torrential rains with more than 50 centimeters of water that have reached the region since Friday. This intense precipitation raised the Guadalupe River to its second highest level ever registered.

According to the American media, in the heart of the night from Thursday to Friday, the Guadalupe increased eight meters in just 45 minutes, immersing the surrounding areas with cut roads and damaged dams.

This situation caused gravisSIMES floods, the authorities that spoke of “ray floods”, defined by the American weather service as floods that “begin in six hours and, often, in three hours, according to heavy rains.”

“The intensity of precipitation, the location and distribution of precipitation, the use of the earth and the topography, the types of vegetation and its growth/density, the type of soil and the soil water content determine the speed with which sudden floods can occur and influence the place where they can occur,” explains the body. Therefore, they are very difficult to predict, both in relation to their intensity and their location.

“We constantly face floods. It is the most dangerous river valley in the United States. When it rains, we have water. But we had no reason to believe that it would look like what happened here, absolutely not,” said Rob Kelly.

A favorable geology to thunderstorms and runoff

In fact, most of the victims were identified in Kerr County, northwest of San Antonio, sometimes nicknamed “the alley of sudden floods.” Three more counties east, crossed by tributaries of the Guadalupe or local rivers, also deplored dead.

In all these areas, limestone is an important geological factor that has accentuated the speed and violence of floods by promoting very fast runoff when soil saturation, according to an expert cited by the American public radio. It is a semi -arid area whose soils are not absorbed.

Texas is the state of the United States most affected by floods. Between 1959 and 2019, 1,069 people died during the floods in Texas. The second highest evaluation is in Louisiana, with 693 dead.

“As is the case during the worst disasters, many elements have combined terriblely,” said meteorologist Robert Henson.

In fact, the region was also affected by a great drought, which further accentuates the phenomenon of runoff, the floors cannot absorb the slightest fall.

Moisture record

As explained by the American hydrologist and professor at the University of Texas Hatim Sharif, this region is particularly subject to heavy rains, due to balcony escarpa, an area of ​​Texas geological failures with a line of steep cliffs.

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“When the hot air of the Gulf hastened there, it condenses and can release a lot of humidity. This water quickly descends the hills, from all sides, filling the currents and rivers below,” said the specialist with the conversation.

In addition, the atmosphere was particularly responsible for moisture due to the recent step of a tropical storm, called Barry, whose system has remained blocked in part of Texas. The geographical location of the state, between cold and dry air in the north and humid and warm air in the Gulf of Mexico, leads to storms and thunderstorms.

Several officials have indicated the role of climate change. Although it is difficult to establish a link between storms and global warming so early after its appearance, the general increase in temperatures means that the atmosphere may contain more water vapor and, therefore, possible rainfall.

According to The Guardian, the data collected this Thursday from the city of the river revealed record levels of moisture in the upper atmosphere over the center of Texas.