Why do people leave? Environmental change motivates human migration

Human migration can be triggered by multiple factors, including political, demographic, economic and social influences. It is widely accepted that environmental change can also drive large populations to migrate to other regions. However, isolating and measuring environment-induced migration to quantify the impact of environmental change is challenging.

It is clear that rapid-onset changes, such as floods and hurricanes, can cause populations to migrate. However, to understand how migration is linked to slow-onset changes — such as land degradation and desertification — is more complex and less obvious. Studies on environment-induced human migration are typically restricted to particular environmental stress factors in particular regions; for instance, droughts in Ethiopia, vegetation changes in Ghana, and changes in rainfall patterns in Burkina Faso all influence human migration patterns in those areas, respectively. Understanding the interplay between environmental pressures and human migration at a global scale, however, remains a challenge.

A study published in the journal of Applied Geography spatially determines for the first time the environmental drivers of human migration on a larger scale. The authors, led by Kathleen Neumann of Wageningen University in The Netherlands,  focus specifically on drylands, which cover 40 percent of the Earth's land surface. Drylands also provide a home for more than 2 billion habitats and support the livelihoods of more than half of the world's impoverished populations.  Using migration data from the Center for International Earth Science Information Network (CIESIN), the authors identify the net number of migrants per kilometer over the entire globe during the period 1970-2000.

They then map spatial patterns of environmental drivers and human migration to identify which environmental changes are most prominent where "out-migration," or the departure of humans from one region to settle in another, occurs in these dryland regions. Their methodology is four-fold. First, they identify the areas of out-migration at the global scale, during the period from 1990-2000, to determine which areas human populations are exiting for any unknown reason. Second, they identify seven major environmental drivers in dryland regions: annual mean precipitation, aridity, drought frequency, land degradation, soil constraints, cropland, and pasture area. Using cluster analysis — a method of classification that groups together similar environmental drivers based on distance — the authors then identify eight clusters to characterize drylands by their general environmental conditions. Third, they map global out-migration and those eight clusters to identify prominent areas of out-migration and the most severe environmental drivers responsible for human relocation. Fourth, they select two areas with high numbers of human out-migration, Northern Brazil and Burkina Faso, to gauge the global scale results with a migration hotspot analysis.

The study then divides the environmental clusters based on whether the most severe environmental drivers were land-related or water-related. Mapping these clusters against out-migration shows that relocation occurs more frequently in areas constrained by land degradation rather than in areas with limited water availability. The migration hotspot analysis shows that while environmental drivers do play an important role in migration processes as a push factor, income opportunities in other areas act as a strong pull factor. It is also important to note that, in some cases, adverse environmental conditions can be partially or completely offset by strong socio-economic governance.

Interest in environment-induced human migration has been growing in recent years. In fact, the issue has been given priority in international agendas despite the lack of a global scale understanding of which environmental factors most severely affect human migration. Thus, the global scale observations made in this study are especially important for their policy implications. The research identifies for the first time the global pattern of environmental pressure factors contributing to out-migration. This global picture confronts typical studies that focus on human migration in particular regions and on the impact of particular environmental factors. The global picture can help identify environmental incentives for migration in drylands based on the eight clusters and their environmental trends. However, when implementing policies, location specific measures are still of high importance to adequately address environmentally motivated human migration and to build resilient and sustainable communities.