Land degradation and desertification represent a major threat to the population and ecosystems of (semi)-arid regions like the Sahel and the Sahara. In 2007, the African Union launched a pan-African programme, the Great Green Wall for the Sahara and the Sahel Initiative (GGWSSI) to reverse land degradation and desertification in the region, improve food security and support local people to adapt to climate change. Within the GGWSSI different kinds of projects have been implemented. In order to quickly evaluate the effectiveness of (a large number of) restoration and sustainable rangeland/agriculture projects, a methodology to remotely assess the biophysical impacts of diverse interventions is desirable.

Within the Administrative Arrangement Technical and scientific Support to agriculture and Food and Nutrition Security we aim to develop a multi-scale remote sensing (RS) based approach to monitor the biophysical impact of sustainable agriculture and rangeland projects. Specifically, we propose to utilize a biophysical indicator obtained via satellite imagery and compare the difference between project sites and corresponding reference sites before and after the intervention. Besides this specific comparison between project and reference sites, the general state and development of vegetation and other parameters (like precipitation) on a larger scale are important information for project planning in general and the project impact assessment. This report focuses on this general analysis of vegetation and precipitation trends in north Senegal and provides some first basic approaches for RS-based impact assessment on biomass increase of selected GGWSSI projects. An upcoming paper will concentrate on a more advanced approach of impact assessment.

Desertification threatens the livelihood of people in the Sahel and the Sahara, which represent one of the world’s poorest population. The United Nations Convention to Combat Desertification defines desertification as “land degradation in arid, semi-arid and dry sub-humid areas resulting from various factors, including climate variation and human activities” (UNCCD 1994). Land degradation itself represents the reduction or loss of biological or economic productivity in dryland ecosystems (Millennium Ecosystem Assessment 2005). Besides physically affecting ecosystems, land degradation causes various socio-economic problems like food insecurity, water shortage, poverty, health problems, and conflicts (Mbow et al. 2015). However, the assessment and quantification of land degradation is challenging due to the complex nature of the phenomena and various data constrains. Due to the scarcity of ground observations in African drylands, remote sensing data has been widely applied to study degradation in this region. Despite four decades of Earth Observation (EO) application, there is no consensus on the direction and magnitude of land degradation in the Sahel (Mbow et al. 2015). While many studies indicate an overall greening of the Sahel, other studies show no trend or even a browning (hence degradation). According to the review of Mbow et al. (2015) these inconsistent conclusions at the regional level from different EO studies could be related to differences in the spatial resolutions and generations of sensor, the study period, the applied remote sensing indices, and the assumptions and utilized computational methods.

In 2007, eleven African countries (Senegal, Mauritania, Mali, Burkina Faso, Nigeria, Niger, Chad, Sudan, Ethiopia, Eritrea, and Djibouti) adopted the Great Green Wall for the Sahara and the Sahel Initiative (GGWSSI) to tackle the adverse social, economic, and environmental impacts of desertification in the region. These countries agreed to join forces in a pan-African reforestation project with the ambition of creating a continuous series of restored ecosystems across the African continent from east to west, in total more than 7000 km. The initial idea has evolved from a tree wall to a vision of mosaic interventions addressing the challenges of the local population. Overall, the GGWSSI aims at strengthening the resilience of the natural systems and the region’s people by thorough ecosystem management and improved living conditions of the population. The GGWSSI supports initiatives of local communities for the sustainable management of rangelands, forests and other natural resources. In addition, it aims at improving the food security in the region and contributing to climate change mitigation and adaptation. In 2012, the African Ministerial Conference on Environment adopted a harmonized strategy for the GGWSSI (African Union & Panafrican Agency of the Great Green Wall 2012). Today many Sahelian and Saharan countries (Algeria, Burkina Faso, Chad, Djibouti, Egypt, Eritrea, Ethiopia, Gambia, Mali, Mauritania, Niger, Nigeria, Senegal, Sudan) as well as different international partners, organisations of the United Nations, non-governmental organisations, and the scientific community are involved in the GGWSSI, including the European Union Delegation to the African Union Commission (e.g., http://www.greatgreenwallinitiative.org/).