The University of Arizona

Climate Change and Human Migration in the Southwest

March 29, 2011
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A blog post circulating around last week caught my attention. It suggested, based on new census data for Texas, that the decline in rural population in arid, central Texas over the last decade was due to the impact of persistent drought on agriculture. As the region dried out, crops withered, and people left. 

Is the recent decline in the rural population of arid central Texas due to drought? Image: U.S. Census

It’s a powerful narrative, but let’s be clear—although this was an interesting blog post, there is no science or quantitative analysis behind the blogger’s suggestion. Other factors—social, economic—could obviously be involved in migration away from a rural area like central Texas during the last decade. For example, as cities grew larger over the last decade, perhaps water rights were transfered from rural farmers to urban and suburban areas, something that is happening in other parts of the West.

But human migration due to climate change is a compelling and important issue that is just beginning to be addressed. Here in the Southwest, migration was an important coping strategy for Native American cultures during the last 1000 years.  There is abundant archeological evidence that shows populations abandoning their homes across the Four Corners during periods of drought in the 12th and 13th centuries (see Benson et al. 2007). These past periods of drought were like nothing we’ve ever experienced in the Southwest. They were intense, widespread, and lasted for decades and decades. Agriculture-based communities that had grown populous during wet periods prior to the droughts just couldn’t sustain themselves in the face of such dry conditions.  So they left.

There is also some evidence of modern climate-driven migration in our region. A novel study was published last summer that links climate, crop yields, and human migration in Mexico. The authors found that climate-induced declines in crop yields were linked to an increase in the number of adult Mexicans migrating to the U.S. They were even able to quantify this relationship: between 1995 and 2005, a 10% decline in crop yields caused 2% of the adult Mexican population to depart for the U.S. (Feng et al. 2010). And they were confident enough to make a projection about future migration based on climate projections: according to the paper, by 2080, climate change will lead to the emigration of 1.4 million to 6.7 million adult Mexicans (2-10% of the adult population).

Predicting human behavior is a complicated venture; by comparison, climate change projections are much simpler and more reliable! However, it is a no-brainer that a more arid future will have an impact on agriculture throughout the Southwest, and migration remains one possible strategy for dealing with the effects of climate change. But our region is no longer comprised mainly of subsistence farmers, so these two studies have limited utility for predicting future migration patterns. How do you think a warmer, drier future will influence human population patterns in our region?