IRI@AGU: Mapping the Sahel’s Re-greening

Alessandra Giannini

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The Sahel region, just south of the Sahara Desert, stretches across Africa from the Atlantic Ocean to the Red Sea. The persistent drought and resulting famines that pummeled the region in the 1970s and 80s were for decades blamed on local societies – on the mismanagement of land resources that manifested itself in cultivating marginal land, in overgrazing and in deforestation associated with cutting wood for fuel. In reaction to this “desertification” narrative, individuals and communities, with varied support from government and non-governmental organizations, responded with innovations based in local knowledge, such as agro-forestry and soil and water conservation, referred to collectively as “sustainable land management”. Since the early 1980s the region has undergone “re-greening”, seen in the positive trend of vegetation cover as indicated by satellite data. At the same time, precipitation has increased, leading to the seemingly intractable question of attributing the change in vegetation to climate or human intervention.

Alessandra Giannini, a research scientist at the International Research Institute for Climate and Society, has been studying precipitation in the Sahel for over 10 years. Giannini’s past research conclusively linked the persistence of drought of the 1970s and 80s to subtle changes in the surface temperature of the global oceans, “freeing farmers of blame”. Giannini and Mimi Stith, a former research assistant and now a doctoral candidate in Anthropology at Boston University, are now attempting to characterize spatial variation in vegetation cover, and relate it to interaction with climate and human intervention. Read the Q&A below for more on her research, and, if you’re going to AGU, stop by her presentation.

Your past research has primarily examined causes of rainfall variability in the Sahel. How does this research complement that work, and what made you take the step in this direction of research?

It is impossible to study the climate of the Sahel and not be intrigued by the multi-decadal history of scientific explanations of drought, from Charney’s bio-geophysical feedback in the 1970s to the UK Met Office’s first climate model experiments that tied drought to global scale variations in sea surface temperature. My analysis that drought could be explained by slowly evolving changes in the surface temperature of the oceans highlighted the role of warming of the equatorial Indian Ocean. At that point it became inevitable to make the connection to anthropogenic climate change, and in that context, to think whether actions taken to adapt to drought could be translated into adaptation to future climate change.

You’ve added social/human dimensions to your analysis of Sahelian regreening. How have you done this?

I was motivated by reading the work of Chris Reij and Stefanie Herrmann, as well as of environmental scientists from the Sahel like Serigne Kandji, Mahamane Larwanou and Abasse Tougiani. Their narrative of local resilience countering the prevalent crisis narrative that we are too accustomed to receiving from Africa appealed to me, and prompted me to try and substantiate it on a regional scale. With small-grant support from the Earth Institute I hired Mimi, who assembled an impressive archive of information on development aid-funded interventions that may have contributed to re-greening. We then matched a regional characterization of environmental change in relation to rainfall variation to the prevalence of interventions.

What has been your most significant finding? Any surprises?

The maps that we drew show nothing surprising, but document the multiple narratives of interaction between climate, land cover and human intervention. Albeit at a coarse spatial scale, they go beyond the case study literature to provide a comprehensive map of environmental change that puts re-greening in context.

The drought in the Sahel appears to be over, does that mean the region is experiencing more consistent rainfall? Why is it important to keep studying the area?

Actually, the rainfall in this region is anything but consistent nowadays! In the past, it was consistently above normal, during the wet decades of the 1950s and 1960s, then consistently below normal, in the 1970s and 1980s. In most recent years it’s been fluctuating a lot, both year to year, and within a season, which makes it all the more imperative that we improve monitoring and prediction. We also need to continue to work behind the scenes to improve our physical understanding of these variations.