This map depicts net migration for dryland areas of the world during the decade of the 1990s, expressed as the net number of migrants per square kilometer. Net migration is the difference between the number of people entering and the number leaving a region in a specified time period. This map is the first global map of net migration that shows migration patterns within countries, not just national totals. The data behind this map can help us understand if people have been moving into, or away from, areas experiencing environmental degradation or stress, or areas highly vulnerable to climatic variability and change. Information of this kind is critical to climate change adaptation planning, among other uses. Net migration is one of two fundamental components of population growth (the other is natural increase, the difference between births and deaths).
Dryland ecosystems are identified by the Millennium Ecosystem Assessment as lands where plant production is limited by water availability and which are characterized by livestock grazing and, to a more limited extent, rainfed crop cultivation. The map illustrates the different patterns of migration within the drylands. Some drylands have experienced a net influx of people (positive numbers shown in red shades). In other areas, more people are leaving than arriving (negative numbers shown in blue shades). The map contains relatively large areas of negative net-migration, very likely rural areas. Concentrated areas of positive net migration tend to cluster around urban areas, for example in the area surrounding New Delhi on the Gangetic plain of North India, as well as in some parts of Turkey and northern Venezuela.
When all the migration into and out of dryland ecosystems is tallied by region, the results can be depicted in a bar chart with negative numbers representing net out-migration and positive numbers representing net in-migration (see graph to the right – blue bars represent the 1990s). As shown, the drylands of Africa and Latin America lost population due to out-migration across all decades, whereas the drylands of North America experienced an increase in migrants. Asia saw fluctuations, but with overall out-migration, and in Europe the out-migration trend in 1970s and 1980s reversed in the 1990s. Magnitudes varied broadly, ranging from -15 million people in Asia to +8 million in North America.
The positive net migration in North America and to some extent also in Europe may reflect the “amenities” offered by drier and sunnier regions (places such as Arizona or the Mediterranean coast), where people move not only for economic reasons but also because these areas are perceived as more desirable than their places of origin. This contrasts with the out-migration from dryland areas in low income regions, where rural inhabitants are moving mostly to urban areas both inside and outside dryland areas. The literature suggests that out-migration from drylands in low income regions stems in part from climate variability, especially the frequency of droughts, and the difficulty in these marginal environments of making a living from traditional, rain-fed forms of agriculture and pastoralism.
Climate change-induced alterations to ecosystems and increases in extreme weather events are increasing risks to local populations, and it is therefore important to know if people are likely in the future to move into, or away from, marginal environments and high risk areas. Our research provides a mixed picture. With the exception of high income regions, there has been movement out of marginal ecosystems with high drought risk such as drylands and mountainous areas, but there has been movement into lowland areas near inland water bodies and the coasts, where economies are thriving. This will put people at greater risk of harm from the hazards characteristic of those regions, such as floods and coastal storms. In the aftermath of Superstorm Sandy, Klaus Jacob of the Lamont-Doherty Earth Observatory has pointed out that people are moving into some of the low lying areas of New York City most exposed to storm surge, and away from higher elevation portions of the city.
This map is an output of a CIESIN project to estimate net migration by ecosystem, commissioned by the United Kingdom’s Foresight Project on Migration and Global Environmental Change. Because data on migration within countries are especially limited, CIESIN used an indirect modeling approach that assessed population change in each decade, subtracted the natural increase or decrease (using as much information as possible on urban-rural differences), and extracted the net migration as a residual. The result is a global grid of net migration, with each grid cell (approximately 1 square kilometer in area) containing an estimate of the number of people who, on balance, moved in or out during each decade. There are uncertainties in this approach, but they tend to be lower at higher levels of aggregation, such as ecosystems. More information on the modeling method is available in the full report for the Foresight Project, and a more detailed examination of migration in marginal and risk prone regions is provided in the article, Migration and Risk, in Environmental Research Letters. Also, a recent article at environmentalresearchweb discusses implications of the research.
This blog is part of the Map of the Month blog series produced by the Center for International Earth Science Information Network (CIESIN). The map and commentary were developed by senior research associate Alex de Sherbinin, with associate research scientist Susana Adamo, geographic information specialist Tricia Chai-Onn, and communications coordinator Elisabeth Sydor.