History leaves traces. It not only leaves traces in the form of monuments or through the culture that is bequeathed, but in natural environments that serve as witnesses of climatic periods that provide lessons for today. The DANA (Isolated Depression at High Levels) that occurred in Valencia or the episodes of torrential rains that are occurring throughout Spain can be studied by looking at the past. An investigation in Guadix (Granada) and the historical series of river floods in Huelva allow us to draw an Andalusian map that explains the DANAS of the future. With a conclusion that is repeated: the storms are becoming more intense and the effects more severe due to the action of man.
Andrés Díez-Herrero, technician at the Geological and Mining Institute of Spain (IGME), led research between 2018 and 2021 in the archaeological excavations of the Roman Theater of Guadix, in Granada, which allows us to speak of the existence of a “climate archive” that It reveals episodes of torrential rains since the 1st century with the climatic conditions that affected eastern Andalusia at that time and, by extension, part of the Levant. A climate archive that, in the words of the specialist, not only left physical traces, but also scientific conclusions that force us to rethink urban planning.
The research, published in the scientific journal Global and Planetary Change, makes it possible to draw parallels and differences between the DANAS of the past and those occurring now. Through radiocarbon dating (C-14) and using an optically stimulated luminescence (OSL) technique, the team led by Díez-Herrero studied the sediments in the archaeological remains in different layers, being able to determine severe climatic episodes, especially in the 1st century and during the Middle Ages.
Global warming as a common factor
At both times, if compared to today, there was a common denominator: global warming. According to the researcher, “the vegetation found then is the usual one in the semi-arid Mediterranean area, which is common both in eastern Andalusia and in much of the Levant.” Therefore, it can be concluded that the climate was similar in Roman times, in the Middle Ages and today, there were periods of warming but it was not as notable as now, the scientists explain. It is not the only thing in which all these periods are similar, according to what is dated, but human action also contributed to making the effects of torrential rains more severe.
This has been verified by seeing the remains that have been found in the different layers analyzed between the years 2018 and 2021. According to scientific research, the DANAS “dragged more sediments than water”, which suggests, according to Díez-Herrero , IGME researcher, that humans from these three eras have built in areas that could flood in periods of high risk of torrential rains. What is striking is that the location of the Roman Theater of Guadix is not among the areas classified as flood-prone, so, according to scientists, it is advisable to review the maps.
“Maps should be reviewed to know where to locate, especially key buildings such as hospitals or fire stations,” points out Andrés Díez-Herrero. Currently, the return period that is usually used to build is that of the climatic episodes of the last 500 years, but different research suggests updating this time period and adapting it to the reality we live in. “These return periods are measured taking into account flooding with clean water from rivers, but not with dirty water from streams, ravines or areas that can flood in the event of torrential rains.”
Climate change and the “acceleration” of episodes
While research into the Roman remains at Guadix suggests that human adaptation to the environment has had a strong impact on the area’s climate, the torrential rains that occur in western Andalusia have other historical peculiarities. Juan Antonio Morales, geologist at the University of Huelva, has studied for years the fluvial cycles of the Guadiana, Tinto and Odiel rivers, which has allowed him to establish solid bases for the behavior of rain and associated flooding.
These episodes, throughout the western arc, are obviously marked by the Atlantic Ocean. “The climatic periods of El Niño and La Niña are what define the torrential rains that fall in this area,” says Morales. Remember that you cannot speak of a “cold drop” in any case in the Atlantic areas because the ocean, unlike what happens in the Levant with the Mediterranean Sea, “is already cold.” The problem is that, also due to human action, “climate change is raising ocean temperatures.”
“We have observed that, although the Atlantic does not usually produce cold drops, El Niño brings warm Mediterranean water, displacing the Atlantic currents and generating episodes of heavy rain in the Gulf of Cádiz.” A trend that is accelerating in recent decades. “We observe that storms are becoming more severe and that they also occur at times when they did not happen before. They almost never happened after March and now we have them in May or June.”
The history, collected in geological dating, also explains the differences between rivers such as the Tinto and the Odiel with one of greater importance such as the Guadiana. In western Andalusia, the Tinto and the Odiel mark the so-called “fluviotidal” floods, which are those that coincide with the overflowing of rivers in areas with marshes, as occurs in Huelva. While the Guadiana is an example that human action can mitigate the effects of climate change. This river is “completely controlled”, thanks to the more than 40 reservoirs along its entire length. “It would be almost impossible today for it to overflow, unless we left all the reservoirs open. Something that could happen in the past,” says Morales.
In any case and with the data in hand, the geologist remembers that what happens in areas like Huelva or Cádiz cannot always be compared to a DANA. In fact, some of the recent torrential rains are not. “Atlantic fronts are common in this area of Spain and, with the passage of time, they become more and more severe.” This occurs because the ocean temperature is rising, but in a stable manner, while the wind fluctuates more rapidly, which means that when both factors come together, the rains are more severe and continuous over time.
Rethink the present
Both Morales and the Díez-Herrero team agree, observing the historical climate models and the traces of the past collected, that it is necessary to “rethink” current urban planning and the way in which the population is educated about flood zones and torrential rains. “More geological knowledge is needed from schools,” says Morales, while IGME researchers believe that the historical periods analyzed are notable enough to “review flood maps and revise urban plans.”
“The design of urban and rural infrastructure in vulnerable areas leads to torrential rains with a large load of solid waste that can clog drains and worsen flooding.” Something that invites us to adapt them to the possible torrential flows that arise. In fact, in the Guadix theater itself, the Romans modified the structure after one of the floods, foreseeing the consequences of future episodes. DANAS episodes that, as has occurred in Valencia, tend to be more common and more severe due to human action that gives rise to global warming and therefore climate change.
#historical #traces #explain #future #Danas #Andalusia #intense #severe #due #human #action
