Storms destroy dry, scorched soil that cannot absorb water at the same time

The parched and bare ground, which has been plagued by drought and fires this summer, is more vulnerable to the torrential rains that are becoming more frequent in Spain. Storms destroy these soils and cannot absorb much water at once.

Arid terrain, especially on slopes, is at high risk of erosion due to the violent passage of water. Very dry soil – especially if it is burnt – loses its ability swallow Water: Remains without vegetation and becomes compacted, so it is less filtered. It can also be waterproof, as demonstrated by a popular video from the University of Reading these days.

The pictures show how the ground wet with green grass absorbs water from an upturned cup. Meanwhile, water does not reach the dry meadow.

“This is a phenomenon known as hydrophobia or water repellency. Although in Spain and everywhere else, with droughts, the soil cracks and in this way they allow infiltration”, explains Albert Sole, geographer associated with the CSIC Arid Zones Station. “It is true that with heat, vegetation produces hydrophobic compounds that reduce water infiltration. It’s temporary, but it can last for a while.”

The meteorologist who recorded the video, Rob Thompson, explained to the BBC that the ground is “potentially as dry as asphalt and can behave that way when it rains”.

“Fire, in addition to eliminating vegetation, can change soil surface characteristics and induce hydrophobicity, which How to laminate soil,” explains José Navarro, professor of environmental sciences at the Miguel Hernández University of Alicante.

And he continues, “It reduces the potential for water infiltration, which is one of the main functions of soil for water penetration and purification. The runoff contributes, and therefore the soil itself, to the erosion and retention of calcined remains, and finally, it contributes to desertification processes”, concludes this chemist and member of the Spanish Soil Science Society (SECS).

Defiance is a much more widespread trait than previously thought”, summarizes the work of two research groups at the Universities of Miguel Hernandez and Seville for SECS.

Erosion, land degradation due to the passage of forest fires, drought, intensive agriculture are the agents of soil degradation, desertification that is progressing in Spain, also due to climate change.

And with the loss of soil—”which is scarce,” recalls José Navarro—ecosystem functions and services are lost. “It will trigger a series of depressing events that will have the effect of reducing water storage capacity and may therefore affect future drought scenarios.”

The lack of rain that Spain has experienced since May “increases the vulnerability of the land to possible torrential rainfall,” explains the professor. It also affects the upper layer of the soil, which is lost without moisture. And the soil filters water more and better if it has organic matter.

This dryness inhibits, but does not eliminate, soil biodiversity (life, especially plant life in the soil). And this biodiversity is “responsible for maintaining soil structure along with organic matter. If it is degraded, water retention and infiltration is lost, contributing to erosion, which is unusual during torrential rains,” the researcher continues.

In almost any situation, if the rainfall exceeds the capacity to absorb water, the liquid will run off, but “in dry years and poorly distributed rains (both scanty and intense) the land reduces the vegetation cover, which happens more. It is protected from erosion,” he said This presentation by professors from the School of Agricultural Engineering of the University of Valladolid. That is, without plants, heavy rain, which sends a lot of water, will pass over the surface.

The point is that Spain has had low rainfall for months. Ecosystems are drying up as no rain has been seen and unusually intense and sustained heat has left them dehydrated. And the other part of the problem is that precipitation is becoming scarcer but more intense: there are fewer wet days, and when clouds do break, they do so in greater amounts. more violently.

floods and floods

State Meteorological Agency Discovered changes in rainfall in Spain (especially on the peninsula and the Balearic Islands). “It rains fewer days a year and it rains more intensely.” What the data shows is an increase in the frequency and severity of situations that cause very heavy or torrential rains in the Spanish Mediterranean“, explains the analysis of Aimet’s delegate in Navarre, Peio Oria. The role of climate change is “a central issue of inquiry”.

In his paper, Oria details that for the 1965-2020 historical series, there are 25 days with very high precipitation accumulation (99.9th percentile), five crowdings from September 2019 to January 2020. It also highlights a large number of events. [extremos] So far in the 21st century and in the decade 2010-2020,” he describes.

The Food and Agriculture Organization of the United Nations (FAO) explains simply: “If the rain is light, there will be less runoff and more infiltration. If the rain is more intense, there will be runoff.”

At the end of this cycle, orography and urban planning have coincided so that heavy runoff after heavy rains causes floods and flash floods. In Spain, according to the classification of the Ministry of Ecological Transition, the areas of land that are particularly vulnerable to flooding reach 12,000 km. In addition, urban expansion has placed nearly 50,000 buildings in riverbeds and hazard zones under little control.

Source: El Diario





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