What is desertification and how can we prevent it?

Did you know that two thirds of Catalonia’s land is vulnerable to desertification? A phenomenon that occurs in arid or semi-arid climates, desertification leads to a vicious circle that causes total soil degradation and which it is very difficult to break out of. Based on today’s climate and the changes it is set to undergo over the coming years, the parts of Catalonia most vulnerable to desertification are the districts of the Ebro River basin and the central districts of the provinces of Tarragona and Lleida. The areas in question have dry subhumid and semi-arid Mediterranean climate conditions, and are experiencing longer and more frequent droughts due to climate change. In some places, furthermore, unsustainable, intensive land use has increased the risk of erosion. 

Prevention is key to avoiding reaching such a situation, and that is exactly what we want to explain in this blog post today, on the World Day to Combat Desertification and Drought. Let’s look at this step by step! 

Most of Earth’s terrestrial life is concentrated in the first 10 cm of soil beneath our feet. This first layer is called the A horizon or the organomineral horizon, and it is often covered by fine layers of plant litter (the O horizon), which are extremely rich in organic matter and vital to the storage of nutrients and water that plants will go on to absorb.

Soil has other, deeper layers, such as the mineral (or B) horizons and, further down still, a horizon of partially altered bedrock (C), just above the consolidated bedrock. Soil is simply the result of fragmentation and weathering turning bedrock’s primary minerals into secondary minerals, which combine with plant residues to create a fertile mixture that sustains plants, fungi, microorganisms, and all the other life that depends on it.

The nature of the soil in any given location is conditioned by four different factors:

1. Parent material: this term, used by edaphologists, can refer to anything from bedrock to other materials like alluvium or colluvium. The soil formation cycle begins with parent material breaking down over time. How quickly soil forms hinges on the quality of the parent rock, which can be harder or softer, depending on the material.
2. Climate: parent rock can break down more quickly in very rainy climates with high temperatures.
3. Organic matter: the more vegetation there is on or near soil, the more likely soil is to form or thicken. Organic matter improves soil’s water retention and infiltration capacities, aiding soil formation and boosting biological activity.
4. Topography: the steeper the slope of the ground is, the more difficult it is for soil to form, because gravity and erosion are obstacles to that happening. Depressions, in contrast, allow for the accumulation of matter and the soil there is thicker. 

There is no standard soil formation rate; the speed of the process depends on the four factors mentioned above. Nonetheless, since soil is a non-renewable resource and — on a human timescale — takes a long time to form, it is often said that the creation of a centimetre of soil takes a hundred years. While this is a simplified explanation, it is not far from the truth and helps us understand that when we lose soil somewhere, it will take centuries to get it back. 

Soil is a living system and it performs functions that are very important for life on Earth. For example, it recycles plant and animal remains (dead wood, fallen leaves and branches, dead insects, etc.) in a decomposition and mineralization process through which enduringly stable organic matter that provides living plants with key nutrients is created. The process in question makes soil an incredible carbon store, capable of sequestering carbon dioxide from the atmosphere for centuries. Additionally, soil filters and cleans water, and acts like a huge sponge to retain it for plants and animals.

When we lose soil, we lose all those functions. That is why soil loss is a major cause for concern and an area in which CREAF has been active for years. 

We know a soil’s degradation is not yet permanent if moderate interventions improve its quality. An example of a moderate intervention would be stopping growing crops on land that is beginning to erode and using it for forestry activities instead; another would be adding compost to improve soil structure and reduce erosion. When even the most drastic interventions can no longer improve a soil’s quality, however, its degradation is said to be irreversible (this is what happens at open-pit mines, for instance). In such cases, the soil needs to be reconstructed from scratch, using artificial soils or technosols.

There are a wide range of processes that cause soil degradation, including:

• Contamination: caused by industrial products or waste, uncontrolled waste dumping, debris, uncontrolled sewage discharges, incorrect use of pesticides and/or fertilizers, old sewers in poor condition, atmospheric pollutant deposition, etc.
• Salinization: caused by a high concentration of salts due to reduced precipitation or irrigation with poor-quality water. 
  Compaction: caused by the use of heavy machinery or other compacting elements (grazing animals, car parks, presence of humans, etc.).
• Poor agricultural management: if soil has been intensively used to grow crops, involving continual deep ploughing, use of pesticides and other chemicals, and constant irrigation, it loses its fertility and the life within it.
• Erosion: when a soil loses material, particularly from its surface layer (the richest layer), it ceases to perform certain functions and becomes degraded.
• Desertification: a process that occurs in arid areas where there is little precipitation and a vicious circle of erosion and loss of soil organic matter can be observed. 

Erosion is the removal of soil from one place to another. For erosion to occur, the material must be carried away by a fluid — either air or water. Wind erosion is rare in Catalonia; water erosion, on the other hand, is more common. 

Water erodes as it flows over the surface of the ground (surface runoff), so the more water that falls, the more erosion there will be. However, another factor in the extent of erosion is the ground’s gradient, which can increase the speed at which the water flows. Additionally, a soil’s ability to absorb water (infiltration capacity) affects its erodibility: a soil that is well structured, i.e. porous and not compacted, will be able to absorb and retain more water, hindering erosion. Finally, the amount of vegetation is also very important. The presence of many plants not only slows the flow of water and protects against soil loss when it rains, but also helps the land act as a sponge thanks to the organic matter the plants provide and the channels their roots leave when they die.

In Catalonia, erosion is on the rise due to a climate change-induced increase in the volume and intensity of torrential rain. Furthermore, warmer temperatures mean that less plant growth is expected in the Mediterranean region, reducing the organic content and the porosity of its soil. And as if that were not enough, climate change can also make fires more frequent in certain areas, which would leave soil unprotected and more vulnerable to erosion. 

Combating climate change is crucial to reversing erosion processes, especially in the Mediterranean.

However, the most effective way to start preventing erosion straight away is to educate people about the best ways to manage soil and the landscape. Prevention is the key to avoiding the soil from eroding. For example: 

• Allowing vegetation on banks to grow, rather than cutting it back, to reduce surface runoff. This entails maintaining plant cover on land vulnerable to erosion (areas where there are slopes, crops, etc.).
• Promoting regenerative agriculture, an approach to farming which targets an increase in organic matter and involves no ploughing (thus reducing compaction, as less machinery is used) and no chemicals (and, thus, no pollution).
• Implementing sustainable, regenerative or holistic silvopasture (managed grazing in woodlands or other land with trees), so that animals can feed without compacting the soil excessively or stripping the land of its plant cover.
• Managing overcrowding and activities in natural settings in areas with vulnerable slopes. Designing paths and, in particular, their drainage correctly to minimize the creation of erosion points. 

Desertification is a process of total soil degradation. It only occurs in arid areas (i.e. where there is little rainfall) and has implications for biodiversity. Soil plays a vital role in this process, which, as we will see now, is a self-reinforcing phenomenon. 

When no rain falls, there is less vegetation, or it grows less, so less organic matter finds its way into the soil. With less organic matter, the soil becomes compacted because it loses its structure (the typical clumps of earth that make it porous). Structure loss and compaction reduce the soil’s water infiltration capacity and result in any water that does fall causing erosion and the loss of organic matter from the surface layer. What little rainfall there may subsequently be will fail to infiltrate the soil and will therefore not be available for the scant remaining vegetation to use, thus further reducing the amount of organic matter reaching the soil. 

Although the same process has taken place naturally as a result of climate changes in the past, desertification is now accelerating worldwide (or occurring in places where it should not occur) due to human activity and the current climate change. Drivers of desertification in the Iberian Peninsula include:

• The climate change-induced increase in aridity and adverse weather events (droughts and torrential rain).
• The declining profitability of many agricultural and forestry activities.
• The intensification of agricultural systems: expansion of irrigation and woody crops on marginal land or of annual cropping, without a clear strategy of sustainable management based on local conditions.
• The increased demand for water (groundwater and surface water alike) for agricultural use in many of Spain’s basins.
• The abandonment of rain-fed farming and agroforestry systems.
• The abandonment of soil and water conservation practices, especially in intensive agricultural systems.
• A lack of management in forest areas.
• The increased fire risk stemming from the expansion of plant biomass.
• The use of productive land for urban expansion, industrial activities, and infrastructure development.
• Rural depopulation and loss of human and social capital: greater difficulties in implementing sustainable land management measures and loss of local knowledge regarding soil and water conservation.
• The growing disconnection (including culturally and emotionally) between primary production systems and the land’s natural resources. 

Desertification can be reversed through long-term planning with a focus on increasing vegetation in the affected area. Successful efforts to restore desertified land have begun with the planting of species resistant to arid conditions. This measure is aimed at reactivating the organic matter cycle, enhancing resistance to erosion, and increasing the retention of rainwater in the soil, ultimately paving the way for the return of less resistant species.

Additionally, on a local scale, alterations can be made to an area’s topography. This might involve using terraces to reduce gradients or establishing a keyline system (comprising channels, ponds and/or furrows) to recover as much of the water that falls on a particular spot as possible.