Climate variability and inter-provincial migration in South America, 1970–2011

Highlights

• Extreme monthly temperatures have the most consistent effects on migration in the region.

• Much of the climate-related inter-province migration is directed toward urban areas.

• Climate effects on migration vary by country and historical climate conditions.

Abstract

We examine the effect of climate variability on human migration in South America. Our analyses draw on over 21 million observations of adults aged 15–40 from 25 censuses conducted in eight South American countries. Addressing limitations associated with methodological diversity among prior studies, we apply a common analytic approach and uniform definitions of migration and climate across all countries. We estimate the effects of climate variability on migration overall and also investigate heterogeneity across sex, age, and socioeconomic groups, across countries, and across historical climate conditions. We also disaggregate migration by the rural/urban status of destination. We find that exposure to monthly temperature shocks has the most consistent effects on migration relative to monthly rainfall shocks and gradual changes in climate over multi-year periods. We also find evidence of heterogeneity across demographic groups and countries. Analyses that disaggregate migration by the rural/urban status of destination suggest that much of the climate-related migration is directed toward urban areas. Overall, our results underscore the complexity of environment-migration linkages and challenge simplistic narratives that envision a linear and monolithic migratory response to changing climates.

Introduction

The effects of catastrophic events (e.g., extreme drought and flooding) on migration in the developing world often draw the attention of the public and policymakers. However, human migration is also consistently linked to less visible but more pervasive forms of climate variability, such as increased temperature (Gray and Mueller, 2012a, Gray and Mueller, 2012b, Marchiori et al., 2012, Bohra-Mishra et al., 2014, Mueller et al., 2014). Although evidence of such effects is much more robust than it was only ten years ago, nearly all existing studies have been relatively narrow in geographic scope (for an exception see Gray and Wise, 2016). As well, diverse methodologies have been applied across these studies. As a result, the extent to which previous findings are generalizable across populations and contexts is an open question.

Our study addresses these limitations by quantifying human migration responses to climate variability using 25 rounds of census microdata from eight South American countries, and applying a common methodology and uniform definitions of migration and climate. This approach allows us to assess the extent to which climate change is affecting migration patterns across a very large geographic region—nearly an entire continent—and across multiple decades. We are also able to test for differences in climate effects according to affected individuals’ sex, age, educational attainment, country of residence, and the type of destination (i.e., urban or rural). Attention to heterogeneity in climate effects is important for our understanding of behavioral responses to environmental change. Variations in response to similar changes in climate suggest systematic differences in the adaptation mechanisms that affected individuals are able or likely to use. Studying such patterns is merited since understanding the contours of how response patterns are distributed is a requisite for designing effective social protection policies vis-à-vis climate impacts. Evidence regarding the composition of climate-induced migration is also necessary to assess the likely social and economic consequences of these migration streams. Recent evidence shows that environmentally-induced migration in developing countries can bear negative consequences on the wages of residents in the receiving communities (Strobl and Valfort, 2015, Maystadt et al., 2016). Yet exactly who these migrants will affect depends on where they go and what skillset they bring to the destination, a question that has motivated large bodies of research on migration in general (Aydemir and Borjas, 2007, Sjaastad, 1962, Todaro, 1969). We begin to address this issue here by considering the characteristics of environmentally-induced migrants and the type of destinations they are moving to.

The remainder of the paper proceeds as follows. In the next section, we review existing evidence regarding climate effects on migration and identify key substantive and methodological limits to existing knowledge. We then outline our research objectives, data, and methodology. Next, we present our estimates of overall climate effects on inter-province migration, and test for heterogeneity across demographic groups. We then present estimates of climate effects on inter-province migration by the rural/urban status of destination using a subset of the data that includes information on destinations. As a final set of analyses, we assess whether the effects of climate variability on inter-province migration vary by country and historical climate conditions. We conclude by discussing our results and identifying implications for future research on this topic.