Abstract

In Ethiopia land degradation through soil erosion is of major concern. Land degradation mainly results from heavy rainfall events and droughts and is associated with a loss of vegetation and a reduction in soil fertility. To counteract land degradation in Ethiopia, initiatives such as the Sustainable Land Management Programme (SLMP) have been implemented. As vegetation condition is a key indicator of land degradation, this study used satellite remote sensing spatiotemporal trend analysis to examine patterns of vegetation between 2002 and 2018 in degraded land areas and studied the associated climate-related and human-induced factors, potentially through interventions of the SLMP. Due to the heterogeneity of the landscapes of the highlands of the Ethiopian Plateau and the small spatial scale at which human-induced changes take place, this study explored the value of using 30 m resolution Landsat data as the basis for time series analysis. The analysis combined Landsat derived Normalised Difference Vegetation Index (NDVI) data with Climate Hazards group Infrared Precipitation with Stations (CHIRPS) derived rainfall estimates and used Theil-Sen regression, Mann-Kendall trend test and LandTrendr to detect changes in NDVI, rainfall and rain-use efficiency. Ordinary Least Squares (OLS) regression analysis was used to relate changes in vegetation directly to SLMP infrastructure. The key findings of the study are a general trend shift from browning between 2002 and 2010 to greening between 2011 and 2018 along with an overall greening trend between 2002 and 2018. Significant improvements in vegetation condition due to human interventions were found only at a small scale, mainly on degraded hillside locations, along streams or in areas affected by gully erosion. Visual inspections (based on Google Earth) and OLS regression results provide evidence that these can partly be attributed to SLMP interventions. Even from the use of detailed Landsat time series analysis, this study underlines the challenge and limitations to remotely sensed detection of changes in vegetation condition caused by land management interventions aiming at countering land degradation.

Highlights

  • In the United Nation’s Convention to Combat Desertification (UNCCD) land degradation is defined as “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”

  • Due the heterogeneity of the landscapes of the areas examined in this study and the fact that human-induced changes are expected to take place at a small spatial scale, this study aimed at exploring the value of using medium resolution Landsat data derived from different sensors for trend analysis at a spatial and temporal scale compatible with the scale of Sustainable Land Management Programme (SLMP) interventions

  • The study area consists of 21 major watersheds which are distributed in three different zones of Ethiopia, in Amhara, Oromia and Tigray, and have mean altitudes between 1200 and 3100 m (Figure 1), mean slopes up to 14.4 degrees and mean annual rainfall between approx. 600 and 1900 mm per watershed

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Summary

Introduction

Degradation of land and soil affects approximately one third of the global land area that is used for agriculture [1], involving livelihoods of more than 1.5 million people [2].Land degradation is of particular concern in developing countries, as this issue poses a threat to food security for a large number of poor people and to local economic activities [3].In the United Nation’s Convention to Combat Desertification (UNCCD) (art. 1f) land degradation is defined as “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”. 1f) land degradation is defined as “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”. Among those processes are soil erosion or long-term loss of Remote Sens. Formation, the removal of soil along drainage lines (channels) by surface water runoff, is one of the apparent consequences of soil erosion in Ethiopia [8]

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