Land degradation

Context

Global soils are under the pressure of multiple threats due to population growth, economic development and climate change. While agricultural systems are a major pillar in global food security, their productivity is currently threatened by many environmental issues triggered by anthropogenic climate change and human activities, such as land degradation. However, the planetary spatial footprint of land degradation processes on arable lands, which can be considered a major component of global agricultural systems, is still insufficiently well understood.

In the future, the negative impact of land degradation on human society is likely to increase. For instance, it is estimated that between 50 and 700 million people could be forced to migrate by 2050 due to synergistic effects of land degradation and climate change. The United Nations (U.N.) Sustainable Development Goals (SDGs) have included Land Degradation Neutrality (LDN) by 2030 as a target (indicator 15.3.1). Currently, different United Nations working groups for example (UNCCD, IPBES, IPCC) are choosing different approaches to measure land degradation, and as such, they consider different regions globally as degraded or being degraded. For SDG 15.3.1 (land degradation neutrality), for example, the maps of UNCCD, IPBES, and IPCC disagree. The reason is that UNCCD and IPBES use as land degradation indicators (a) land productivity, (b) land use, and carbon stocks (c) above and (d) below ground, but disregard explicit indicators for soil erosion and other physical soil processes. However, article 1 of the UNCCD defines land degradation from a more soil centric view point as a, “reduction or loss, in arid, semi-arid and dry sub-humid areas, of the biological or economic productivity and complexity of rainfed cropland, irrigated cropland, or range, pasture, forest and woodlands resulting from land uses or from a process or combination of processes, including processes arising from human activities and habitation patterns, such as: (i) soil erosion caused by wind and/or water; (ii) deterioration of the physical, chemical and biological or economic properties of soil; and (iii) long-term loss of natural vegetation” . Conversely, IPCC follows the opposite approach by using globally modelled soil erosion as their key metric for land degradation .

For a more effective implementation of LDN, new knowledge and additional data on global land degradation patterns are needed. We present the recent scientific/research developments towards an improvement of Land Degradation Methodology. We propose some improved methodologies which can improve the efforts of the UN working groups into a consistent and more encompassing approach.

Land degradation in Europe

To address the complex issue of land multi-degradation, a multi-process modelling approach of Land Degradation (LD) is essential in Europe. This approach can be crucial for applying various agricultural (e.g. Common Agricultural Policy), climate (the European Green Deal), and sustainable development (Sustainable Development Goals – SDGs)  policies on the continent. Consequently, a comprehensive analysis of LD can define a powerful decision-making support tool for European and national policies designed to mitigate LD hotspots and support food security, climate stability, and environmental sustainability throughout the continent.

In line with these strategic policies, we modeled, quantified and mapped the convergence pattern of twelve LD processes in Europe using the latest state-of-the-art datasets. Our entire analysis is focused on continental (pan-European) agricultural environments, which are critically important for food production, but generally highly vulnerable to multi-degradation. Essentially, our research integrates a complex set of LD processes that are strategically important to continental agricultural productivity, thus trying to provide a solid scientific basis for a more realistic and efficient implementation of LD-related policies across Europe.

We used a large set of geospatial data including twelve LD processes (water erosion, wind erosion, soil organic carbon loss, soil salinization, soil acidification, soil compaction, soil nutrient imbalances, soil pollution via pesticides, soil pollution via heavy metals, vegetation degradation, groundwater decline, aridity), which are highly representative for agricultural productivity and that were collected from various sources (n = 6) or developed in this study (n = 6). An overview of individual drivers of degradation is provided in Figure below, which provides their essential spatial characteristics before examining the continental status of multiple converging (co-occurring) processes across Europe.

By fusing the twelve geospatial databases, we created Land Multi-degradation Index (LMI) , which highlights the number of interacting processes throughout the continent. LMI revealed between one and ten co-occurring processes in Europe, which were grouped into five degradation classes (the “No degradation” class was approached separately, as it entails the absence of degradation conditions) – very low (1 process identified at pixel level), low (co-occurrence of 2 LD processes), medium (3), high (4) and very high (≥5). Considering LMI classes 1–3, we observed that large parts of the two land use categories are exposed to one (up to 27% of the European agricultural/arable area), two (up to 35%), and three (22%) drivers of degradation. Also, we found that 10–11% of pan-European agricultural/arable landscapes are cumulatively affected by four and at least five concurrent land degradation processes, thus highlighting the most important land degradative hotspots throughout the continent.

Data: This dataset includes the Land Multi-degradation Index (LMI) for arable and agricultural lands and data from 12 indicators which were compiled to develop the LMI.

Reference: Prăvălie, R., Borrelli, P., Panagos, P., Ballabio, C., Lugato, E., Chappell, A., Miguez-Macho, G., Maggi, F., Peng, J., Niculiță, M. and Roșca, B., Patriche, C.,Dumitrașcu, M., Bandoc, G., Nita, I.A. and Birsan, M.V. 2024. A unifying modelling of multiple land degradation pathways in Europe. Nature Communications, 15(1), 3862. DOI: 10.1038/s41467-024-48252-x

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Land degradation in global arable lands

Five degradation processes (aridity, vegetation decline, soil erosion, soil salinization and soil organic carbon decline) were considered to have a major influence on land productivity and analyzed spatially strictly within the world’s arable boundaries. In a first research study, we attempted to analyze the multidimensional presence of land degradation processes in global arable lands, using complex geospatial data that were explored globally.

By applying geostatistical techniques that are representative for identifying the incidence of the five land degradation processes in global arable lands, results showed that aridity is by far the largest singular pressure for these agricultural systems, affecting ~40% of the arable lands' area, which cover approximately 14 million km2 globally. Also, it was found that soil erosion is another major land degradation pathway, affecting ~20% of global arable systems. The two land degradation pathways simultaneously affect an additional ~7% of global arable lands, which makes this synergy the most common form of multiple pressure of land degradative conditions across the world's arable areas.

Data: This dataset package includes two TIFF files: (a) the  number of land degradation processes and b) the types of land degradation processes in arable lands.

Reference: Prăvălie, R., Patriche, C., Borrelli, P., Panagos, P., Roșca, B., Dumitraşcu, M., Nita, I.A., Săvulescu, I., Birsan, M.V. and Bandoc, G. 2021. Arable lands under the pressure of multiple land degradation processes. A global perspective. Environmental Research, 194, art no .110697.

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Global Land degradation as ‘debts’

Building on the idea of a ‘land, soil and carbon debt’, defined as the difference in each land degradation indicator's current value and what it would be without human intervention, or in a native condition. We define as environmental debt:  (a) the difference between natural forest potential and actual tree cover globally, and aggregated by latitude and by world region, (b) the difference between natural soil erosion and actual soil erosion globally, and aggregated by latitude and by world region, (c) the difference between natural above-ground carbon and actual above-ground carbon globally, and aggregated by latitude and by world region, (d), the difference between natural below-ground carbon and current below-ground (0–30 cm) carbon globally, and aggregated by latitude and by world region.

Global tree cover debt, naturally, there could be 4.6 Gha of tree cover but currently there are only 3.2 Gha, so the global tree cover debt is 1.4 Gha (correspondingly, if we define forests as areas with >10% tree cover, naturally there could be 8.8 Gha, currently there are 5.9 Gha, and the implied forest debt is then 2.9 Gha; The natural rate of soil erosion would be 10 Gt per year, but currently, it is 36 Gt. Thus, global soil erosion debt is 26 Gt –and rising.  The above-ground biomass would naturally be 871 Gt C, but currently, it is only is 601 Gt C . This means that global above-ground carbon debt is 270 Gt C.  Below-ground carbon, naturally, there would be 899 Gt C, but currently, there are only 863 Gt C, which means that global below-ground carbon debt is 36 Gt C .

Data: This dataset includes four TIFF files corresponding to as ‘debts’ for a) tree cover,  b) soil erosion c) above ground carbon d) below ground carbon.

Reference:  Wuepper, D., Borrelli, P., Panagos, P., Lauber, T., Crowther, T., Thomas, A. and Robinson, D.A., 2021. A ‘debt’ based approach to land degradation as an indicator of global change. Global Change Biology, 27(21): 5407-5410.