Exploring the relationship between annual soil loss and formation rate in different land use scenarios using support vector machine (SVM) learning models in Tigray Highlands – Nature

Report on Soil Degradation and Sustainable Development in the Kola Embahasti Watershed, Ethiopia

Executive Summary

This report presents a quantitative assessment of soil degradation in the Kola Embahasti Watershed, Tigray Highlands, Ethiopia, analyzed through the lens of the United Nations Sustainable Development Goals (SDGs). An integrated modeling approach, combining the Revised Universal Soil Loss Equation (RUSLE), Support Vector Machine (SVM) learning for land use classification, and a physiochemical model for soil formation, was employed to calculate the watershed’s soil budget. The findings reveal a critical imbalance that directly threatens regional sustainability. The mean annual soil loss was calculated at 61.29 t ha⁻¹ yr⁻¹, while the mean soil formation rate was only 2.45 t ha⁻¹ yr⁻¹. This results in a net annual soil loss of 58.84 t ha⁻¹ yr⁻¹, a rate approximately 25 times faster than natural regeneration. This severe degradation poses a direct threat to SDG 2 (Zero Hunger) by undermining agricultural productivity and food security. Furthermore, the extensive net soil loss indicates a failure to meet the objectives of SDG 15 (Life on Land), particularly Target 15.3 concerning Land Degradation Neutrality. The study identifies land use as the primary determinant of this imbalance, with bare and cultivated lands showing the most significant soil deficits. Urgent, targeted interventions, including afforestation and sustainable land management, are recommended to restore the soil balance and align regional land use practices with the 2030 Agenda for Sustainable Development.

1.0 Introduction: Land Degradation as an Obstacle to Sustainable Development

1.1 The Global and Local Context

Land degradation, primarily through soil erosion, is a significant global challenge that impedes progress towards multiple Sustainable Development Goals. The annual loss of 75 billion metric tons of soil from agricultural lands jeopardizes global food systems, directly impacting SDG 2 (Zero Hunger) and exacerbating rural poverty, a key concern of SDG 1 (No Poverty). In Ethiopia, this challenge is particularly acute. Rapid population growth has driven agricultural expansion and deforestation, leading to some of the highest soil erosion rates in the world. The Tigray Highlands, including the Kola Embahasti Watershed, exemplify this crisis, where land degradation threatens the livelihoods of communities dependent on subsistence agriculture.

1.2 Study Objectives in Relation to SDG 15

This study was designed to provide a quantitative foundation for evidence-based policymaking aimed at achieving sustainable land management. The primary goal is to assess the watershed’s progress toward SDG Target 15.3, which calls for combating desertification and restoring degraded land to achieve a land-degradation-neutral world. To this end, the study pursued the following objectives:

1. To estimate the mean annual rates of soil loss and soil formation for each land use type.
2. To determine the net annual soil balance at both watershed and land use levels, providing a clear metric of land degradation.
3. To analyze the relationship between soil loss and formation rates to understand the dynamics of degradation.
4. To propose targeted conservation strategies that align with the principles of SDG 15 (Life on Land) and support other interconnected goals such as SDG 13 (Climate Action).

2.0 Methodology for Assessing Land Degradation

2.1 Study Area: Kola Embahasti Watershed

The research was conducted in the 4,795.37-hectare Kola Embahasti Watershed in the Tigray region of Northern Ethiopia. The area is characterized by a significant altitudinal gradient (1908 to 3450 m.a.s.l.) and is dominated by subsistence agriculture. Cultivated land comprises 43.97% of the area, followed by shrub/bush land (31.48%) and bare land (16.09%), highlighting the intense human pressure on the landscape.

2.2 Data Sources

A multi-source data approach was utilized to ensure a comprehensive analysis:

• Satellite Imagery: High-resolution Sentinel-2B imagery (10m) for Land Use/Land Cover (LULC) classification.
• Topographic Data: ALOS PALSAR Digital Elevation Model (DEM) with 12.5m resolution.
• Soil Data: FAO/UNESCO Digital Soil Map of the World, supplemented with field measurements.
• Climate Data: 10-year time series (2011–2020) of precipitation and temperature data from the Climate Research Unit (CRU).
• Field Data: Ground truth points collected via GPS for LULC validation.

2.3 Integrated Modeling Framework

A three-part modeling framework was implemented to calculate the net soil balance, a key indicator for monitoring SDG Target 15.3.

1. Soil Loss Estimation: The Revised Universal Soil Loss Equation (RUSLE) was used to estimate mean annual soil loss. A Support Vector Machine (SVM) algorithm was employed for accurate LULC classification, a critical input for the RUSLE model.
2. Soil Formation Rate Estimation: A process-based physiochemical model was developed. It integrated physical weathering (modeled as a function of soil depth), chemical weathering (using the Arrhenius equation), and biological contributions from organic matter.
3. Net Soil Balance Calculation: The final net soil balance was computed by subtracting the annual soil formation rate from the annual soil loss rate. Positive values indicate a soil deficit (degradation), while negative values signify a surplus (stability or regeneration).

3.0 Results: A Critical Soil Sustainability Deficit

3.1 Watershed-Level Soil Loss and Formation Rates

The analysis revealed a profound imbalance between soil depletion and regeneration across the watershed. The mean annual soil loss was estimated at 61.29 t ha⁻¹ yr⁻¹, a rate that far exceeds the widely accepted tolerable limit of 10 t ha⁻¹ yr⁻¹. In stark contrast, the mean annual soil formation rate was only 2.45 t ha⁻¹ yr⁻¹. This disparity results in a watershed-wide net soil loss of 58.84 t ha⁻¹ yr⁻¹, indicating that the land’s natural capital is being depleted at an unsustainable rate. This finding highlights a significant challenge to achieving food security (SDG 2) and maintaining ecosystem integrity (SDG 15).

3.2 Impact of Land Use on the Soil Balance

Land use was identified as the most critical factor influencing the soil budget. The results underscore the importance of land cover in achieving land degradation neutrality.

• Bare Land: Exhibited the most severe degradation, with a net soil loss of 93.02 t ha⁻¹ yr⁻¹. These areas represent a complete failure of land management and are hotspots for desertification, directly contravening the goals of SDG 15.
• Cultivated Land: As the dominant land use, this category showed a high net soil loss of 34.03 t ha⁻¹ yr⁻¹. This finding indicates that current agricultural practices are unsustainable and actively undermine the resource base needed for long-term food production (SDG 2).
• Dense Forest: Demonstrated a state of near-equilibrium, with a negligible net soil loss of only 0.24 t ha⁻¹ yr⁻¹. This highlights the vital role of forest ecosystems in soil conservation, water regulation, and carbon sequestration, contributing to both SDG 15 (Life on Land) and SDG 13 (Climate Action).

3.3 Correlation Between Soil Loss and Formation

A strong negative correlation (r = –0.78) was found between soil loss and soil formation rates. This inverse relationship signifies a dangerous feedback loop: as land becomes more degraded and loses its protective vegetation, its capacity for natural regeneration diminishes, accelerating the degradation process. This dynamic pushes the ecosystem further away from the sustainability thresholds defined by the SDGs.

4.0 Discussion: Implications for Sustainable Land Management

4.1 Drivers of Unsustainable Land Use

The severe soil deficit in the Kola Embahasti watershed is driven by a combination of factors. Steep topography and intense seasonal rainfall create a high potential for erosion. However, this potential is realized through human activities, primarily the conversion of natural vegetation to cultivated land and subsequent over-exploitation. Conventional agricultural practices, such as downslope plowing and inadequate soil conservation measures, exacerbate soil loss. This situation underscores the urgent need for a transition towards sustainable agricultural systems that can support livelihoods without degrading the environment, a core principle of SDG 2 and SDG 15.

4.2 The Critical Soil Budget Imbalance and SDG Target 15.3

The total net soil deficit for the watershed is estimated at over 165,000 tons per year. This figure serves as a stark indicator of the region’s failure to achieve Land Degradation Neutrality (SDG Target 15.3). The current trajectory points towards continued loss of agricultural productivity, reduced water quality due to sedimentation (impacting SDG 6), and diminished resilience to climate change. Reversing this trend requires a paradigm shift in land management, focusing on restoring the balance between soil loss and formation.

5.0 Conclusion and Recommendations for SDG Alignment

5.1 Summary of Findings

This study provides conclusive evidence of a severe soil sustainability imbalance in the Kola Embahasti watershed, driven by unsustainable land use practices. The rate of soil loss vastly outpaces natural soil formation, leading to a significant net deficit that compromises the region’s ability to achieve key Sustainable Development Goals, particularly those related to hunger, poverty, and terrestrial ecosystems.

5.2 Strategic Recommendations

To address this critical issue and align land management with the 2030 Agenda, the following strategic interventions are recommended:

1. Targeted Ecosystem Restoration: Implement large-scale afforestation and reforestation programs on bare and severely degraded lands. This will reduce erosion, enhance soil formation, and contribute to carbon sequestration, directly supporting SDG 15 (Life on Land) and SDG 13 (Climate Action).
2. Promotion of Sustainable Agricultural Practices: Introduce and scale up conservation agriculture techniques, including terracing, agroforestry, and the use of cover crops on cultivated lands. These measures will reduce soil loss, improve soil health, and enhance food security, thereby advancing SDG 2 (Zero Hunger).
3. Integrated Watershed Management: Adopt a holistic watershed management approach that considers the interconnectedness of land use, water resources, and community livelihoods. This ensures that interventions are synergistic and contribute to multiple SDGs simultaneously.
4. Establish a Monitoring Framework: Develop and implement a monitoring system to track key indicators of land degradation, such as the net soil balance. This will enable adaptive management and provide the necessary data to report on progress towards SDG Target 15.3.

1. Which SDGs are addressed or connected to the issues highlighted in the article?

1. SDG 2: Zero Hunger

   The article directly connects soil degradation to agricultural sustainability and food security. It states that soil erosion “jeopardizes food production capabilities and intensifies food shortages for an increasing population.” The study’s focus on the Tigray Highlands, where “subsistence agriculture serves as the principal means of livelihood,” highlights how soil loss is a “significant challenge to agricultural productivity.” This directly relates to SDG 2, which aims to end hunger, achieve food security, improve nutrition, and promote sustainable agriculture.

2. SDG 15: Life on Land

   This is the most central SDG to the article. The study’s primary focus is on quantifying “extensive soil degradation” and “soil erosion” in the Tigray Highlands. It explicitly discusses issues such as deforestation, the impact of different land cover types (bare land vs. dense forest) on soil loss, and the urgent need for conservation. The article’s goal is to “protect soil resources, and promote sustainable land management,” which aligns perfectly with SDG 15’s mission to protect, restore, and promote the sustainable use of terrestrial ecosystems, sustainably manage forests, combat desertification, and halt and reverse land degradation.

2. What specific targets under those SDGs can be identified based on the article’s content?

• SDG 2: Zero Hunger

  • Target 2.4: Ensure sustainable food production systems and implement resilient agricultural practices.

    The article identifies that current agricultural practices in the study area are unsustainable, with cultivated land experiencing a “net loss of 34.03 tons per hectare per year.” It highlights that these practices, combined with deforestation and overgrazing, lead to declining soil fertility and agricultural productivity. The recommendation to implement “sustainable land management” and “sustainable farming methods” is a direct call to action to achieve this target by improving land and soil quality to ensure long-term food production.

• SDG 15: Life on Land

  • Target 15.1: Ensure the conservation, restoration and sustainable use of terrestrial and inland freshwater ecosystems and their services, in particular forests…mountains and drylands.

    The study is conducted in the “Tigray Highlands,” a mountain ecosystem. It quantifies the degradation of this ecosystem and emphasizes the role of forests in maintaining soil stability. The findings that dense forests have the lowest erosion rates and are in a state of “near-equilibrium” underscore the importance of conserving and restoring these specific ecosystems as outlined in Target 15.1.

  • Target 15.2: Promote the implementation of sustainable management of all types of forests, halt deforestation, restore degraded forests and substantially increase afforestation and reforestation.

    The article contrasts the high erosion on bare land with the low erosion in forested areas, noting that population growth has led to “significant deforestation for agricultural expansion.” One of the key recommendations based on the study’s findings is “afforestation.” This directly addresses the call to halt deforestation and increase forest cover to combat land degradation.

  • Target 15.3: By 2030, combat desertification, restore degraded land and soil… and strive to achieve a land degradation-neutral world.

    This target is at the core of the article’s analysis. The entire study is designed to quantify the imbalance between soil loss and soil formation to assess land degradation. The calculation of a “net annual soil loss of 58.84 t ha⁻¹ yr⁻¹” is a direct measurement of the region moving away from land degradation neutrality. The article identifies “bare land” and “cultivated land” as critical hotspots for degradation and calls for “targeted interventions” to restore this degraded land and soil.

3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?

Yes, the article provides several quantitative indicators that can be used to measure progress:

• Indicator for Target 15.3 (Proportion of land that is degraded over total land area)

  The article provides direct, quantifiable data on the rate of land degradation. Progress can be measured using the following metrics from the study:

  • Mean Annual Soil Loss: The watershed-wide average is 61.29 t ha⁻¹ yr⁻¹. This serves as a baseline indicator of the severity of erosion.
  • Mean Soil Formation Rate: The calculated rate is 2.45 t ha⁻¹ yr⁻¹. This value helps contextualize the severity of the soil loss.
  • Net Soil Balance: The study calculates a “net annual soil loss of 58.84 t ha⁻¹ yr⁻¹,” which is a primary indicator of land degradation. Reducing this number towards zero would signify progress towards land degradation neutrality.
  • Land-Use Specific Degradation Rates: The article provides detailed rates for different land cover types, such as a net loss of 93.02 t ha⁻¹ yr⁻¹ on bare land and 34.03 t ha⁻¹ yr⁻¹ on cultivated land. These can be used to track the effectiveness of targeted interventions.

• Indicator for Target 15.1 and 15.2 (Forest area as a proportion of total land area)

  The article’s land use/land cover (LULC) classification provides a baseline for forest cover against which future progress (through afforestation) can be measured:

  • Dense Forest Cover: Constitutes 3.30% of the total watershed area.
  • Open Forest Cover: Constitutes 4.07% of the total watershed area.

  An increase in these percentages over time would be a clear indicator of progress towards halting deforestation and increasing reforestation.

4. Create a table with three columns titled ‘SDGs, Targets and Indicators” to present the findings from analyzing the article. In this table, list the Sustainable Development Goals (SDGs), their corresponding targets, and the specific indicators identified in the article.

Source: nature.com