Measuring the Environmental Dimensions of Human Migration: The Demographer's Toolkit

Relationship among weather variation, agricultural production, and migration: A systematic methodological review

Background and Aims

Two main problems the globe currently facing are migration and weather variation. Weather change has a significant impact on the agricultural industry, which affects the majority of poor people. There is a dearth of adequate methodological documentation when examining the relationship between weather variation, agricultural output, and migration. We aimed to identify methodological reporting difficulties by reviewing the quantitative literature on weather-related migration through agricultural channels.

Methods

A systematic evaluation was conducted using papers published between January 2010 and June 2022, indexed in the SCOPUS, PUBMED, and Google Scholar databases. Using inclusion/exclusion criteria, we selected 22 original research articles out of 18,929 distinct articles for review, in accordance with the PRISMA guidelines. We extracted data from each study to understand how various concepts, research designs, and investigative techniques influence our understanding of migration patterns related to weather in the agricultural sector.

Results

The majority (64%) of the study's data consisted of time series data. In 50% of the studies, secondary data were used. Additionally, 55% of these studies did not state the sample size. In 40% of the studies, model assumptions were fully adhered to, whereas in 36% of the studies, they were not followed at all. The majority of the articles used the Ordinary Least Squares technique, while about 41% applied the Two-Stage Least Squares technique. Various tests were conducted across these studies, such as robustness checks (59.1%), endogeneity tests (31.8%), omitted variable bias tests (22.7%), sensitivity analyses (22.7%), and weak instrument tests (13.6%), to name a few. In the research we selected, the methodology section had various shortcomings and lacked organization. Furthermore, the justifications for deviations from model assumptions were unclear, potentially affecting the study outcomes.

Conclusion

This study has important indications for researchers in studying climatic (weather) migration through agricultural channels besides for policymakers by giving a thorough review of the methods and techniques.

Child Fostering in a Changing Climate: Evidence from Sub-Saharan Africa

An extensive social science literature has examined the effects of climate change on human migration. Prior studies have focused largely on the out-migration of working-age adults or entire households, with less attention to migration and other forms of geographic mobility among other age groups, including youth. In this study, we focus on the implications of climate variability for the movement of children by examining the association between climate exposures and the in- and out-fostering of children in sub-Saharan Africa. We link high-resolution temperature and precipitation records to data from the Demographic and Health Surveys for 23 sub-Saharan African countries. We fit a series of regression models to measure the overall associations between climate exposures and each outcome, and then evaluate whether these associations are moderated by socioeconomic status, the number of children in the household, and the prevalence of fostering in each country. Precipitation is positively associated with in-fostering overall, and these effects are especially strong among households who already have at least one child and in countries where child fostering is common. We find no overall relationship between either temperature or precipitation exposures and out-fostering, but we do detect significant effects among households with many children and those with more-educated heads. In sum, our findings suggest climate variability can influence child mobility, albeit in complex and in some cases context-specific ways. Given the socioeconomic and health implications of fostering, these results underline another pathway through which climate exposures can affect children's wellbeing. More broadly, this study shows that new attention to the links between climate variability, child fostering, and other understudied forms of spatial mobility is needed to fully understand the effects of climate change on human populations.

Environmental migration as short- or long-term differences from a trend: A case study of Hurricanes Katrina and Rita effects on out-migration in the Gulf of Mexico

An environmental event that damages housing and the built environment may result in either a short- or long-term out-migration response, depending on residents' recovery decisions and hazard tolerance. If residents move only in the immediate disaster aftermath, then out-migration will be elevated only in the short-term. However, if disasters increase residents' concerns about future risk, heighten vulnerability, or harm the local economy, then out-migration may be elevated for years after an event. The substantive aim of this research brief is to evaluate hypotheses about short- and long-term out-migration responses to the highly destructive 2005 hurricane season in the Gulf of Mexico. The methodological aim is to demonstrate a difference-in-differences (DID) approach analyzing time series data from Gulf Coast counties to compare short- and long-differences in out-migration probabilities in the treatment and control counties. We find a large short-term out-migration response and a smaller sustained increase for the disaster-affected coastal counties.

Natural resources modulate the nexus between environmental shocks and human mobility

In the context of natural resource degradation, migration can act as means of adaptation both for those leaving and those supported by remittances. Migration can also result from an inability to adapt in-situ, with people forced to move, sometimes to situations of worse or of the same exposure to environmental threats. The deleterious impacts of resource degradation have been proposed in some situations to limit the ability to move. In this contribution, we use remote sensed information coupled with population density data for continental Africa to assess quantitatively the prevalence of migration and immobility in the context of one cause of resource degradation: drought. We find that the effect of drought on mobility is amplified with the frequency at which droughts are experienced and that higher income households appear more resilient to climatic shocks and are less likely to resort to mobility as an adaptation response.

Time to Mainstream the Environment into Migration Theory?

As with all social processes, human migration is a dynamic process that requires regular theoretical reflection; this article offers such reflection as related to the role of the natural environment in contemporary migration research and theory. A growing body of evidence suggests that environmental contexts are increasingly shifting social and ecological realities in ways that are consequential to migration theory. We review some of this evidence, providing examples applicable to core migration theories, including neoclassical economic and migration systems perspectives, the "push-pull" framework, and the new economics of labor migration. We suggest that neglecting consideration of the natural environment may yield misspecified migration models that attribute migration too heavily to social and economic factors particularly in the context of contemporary climate change,. On the other hand, failure to consider migration theory in climate scenarios may lead to simplistic projections and understandings, as in the case of "climate refugees". We conclude that migration researchers have an obligation to accurately reflect the complexity of migration's drivers, including the environment, within migration scholarship especially in the context of global climate change.

Flood vulnerability assessment in the Jamuna river floodplain using multi-criteria decision analysis: A case study in Jamalpur district, Bangladesh

Flood is one of the most common hazards in many countries, affecting both life and properties. The recent climatic changes have brought a rise in both flood frequency and intensity making this phenomenon more devastating to people. Especially, the riparian communities of Jamalpur along the Jamuna river suffer at least once every year accounting for this natural hazard. In a scenario like this, precaution is a crucial task to fight against this natural phenomenon. Therefore, this study attempts to identify the flood vulnerable zones of Jamalpur district situating beside Jamuna river with a multi-criteria analysis. Assessment of flood vulnerability included consideration of physical indicators like rainfall, drainage density, distance from river, slope, land use land cover, elevation, soil classes as well as social indicators like population density, female density, literacy rate, number of shelters, unmetalled road and number of health personnel. All these parameters were analyzed in Geographic Information System (GIS) and assigned weightage with a multi-criteria decision-making technique namely- Analytic Hierarchy Process (AHP). Finally, a flood vulnerability map was generated for the seven Upazilas of Jamalpur district. Very high, high, moderate and low vulnerable zones were identified after overlaying all physical and social indicator maps under consideration. 45.96% portion of a total of 2115.2 sq. Km. Area was under very high and highly vulnerable zones in the final vulnerability map of Jamalpur. Such type of assessment process is significant for flood mitigation projects with a view to providing the greatest concern to the most vulnerable zones. The vulnerability maps can also help the policymakers to provide emergency aids and other privileges to those who are in most need of it.

Migration as a Vector of Economic Losses From Disaster-Affected Areas in the United States

We introduce the consideration of human migration into research on economic losses from extreme weather disasters. Taking a comparative case study approach and using data from the Federal Reserve Bank of New York/Equifax Consumer Credit Panel, we document the size of economic losses attributable to migration from 23 disaster-affected areas in the United States before, during, and after some of the most costly hurricanes, tornadoes, and wildfires on record. We then employ demographic standardization and decomposition to determine if these losses primarily reflect changes in out-migration or the economic resources that migrants take with them. Finally, we consider the implications of these losses for changing spatial inequality in the United States. While disaster-affected areas and their populations differ in their experiences of and responses to extreme weather disasters, we generally find that, relative to the year before an extreme weather disaster, economic losses via migration from disaster-affected areas increase the year of and after the disaster, these changes primarily reflect changes in out-migration (vs. the economic resources that migrants take with them), and these losses briefly disrupt the status quo by temporarily reducing spatial inequality.

The Childhood Origins of Climate-Induced Mobility and Immobility

The literature on climate exposures and human migration has focused largely on assessing short-term responses to temperature and precipitation shocks. In this paper, we suggest that this common coping strategies model can be extended to account for mechanisms that link environmental conditions to migration behavior over longer periods of time. We argue that early-life climate exposures may affect the likelihood of migration from childhood through early adulthood by influencing parental migration, community migration networks, human capital development, and decisions about household resource allocation, all of which are correlates of geographic mobility. After developing this conceptual framework, we evaluate the corresponding hypotheses using a big data approach, analyzing 20 million individual georeferenced records from 81 censuses implemented across 31 countries in tropical Africa, Latin America, and Southeast Asia. For each world region, we estimate regression models that predict lifetime migration (a change in residence between birth and ages 30-39) as a function of temperature and precipitation anomalies in early life, defined as the year prior to birth through age four. Results suggest that early-life climate is systematically associated with changes in the probability of lifetime migration in most regions of the tropics, with the largest effects observed in sub-Saharan Africa. In East and Southern Africa, the effects of temperature shocks vary by sex and educational attainment and in a manner that suggests women and those of lower socioeconomic status are most vulnerable. Finally, we compare our main results with models using alternative measures of climate exposures. This comparison suggests climate exposures during the prenatal period and first few years of life are particularly (but not exclusively) salient for lifetime migration, which is most consistent with the hypothesized human capital mechanism.

A machine learning analysis of drought and rural population change on the North American Great Plains since the 1970s

Machine learning techniques have to date not been widely used in population-environment research, but represent a promising tool for identifying relationships between environmental variables and population outcomes. They may be particularly useful for instances where the nature of the relationship is not obvious or not easily detected using other methods, or where the relationship potentially varies across spatial scales within a given study unit. Machine learning techniques may also help the researcher identify the relative strength of influence of specific variables within a larger set of interacting ones, and so provide a useful methodological approach for exploratory research. In this study, we use machine learning techniques in the form of random forest and regression tree analyses to look for possible connections between drought and rural population loss on the North American Great Plains between 1970 and 2020. In doing so, we analyzed four decades of population count data (at county-size spatial scales), monthly climate data, and Palmer Drought Severity Index scores for Canada and the USA at multiple spatial scales (regional, sub-regional, national, and county/census division levels), along with county level irrigation data. We found that in some parts of Saskatchewan and the Dakotas - particularly those areas that fall within more temperate/less arid ecological sub-regions - drought conditions in the middle years of the 1970s had a significant association with rural population losses. A similar but weaker association was identified in a small cluster of North Dakota counties in the 1990s. Our models detected few links between drought and rural population loss in other decades or in other parts of the Great Plains. Based on R-squared results, models for US portions of the Plains generally exhibited stronger drought-population loss associations than did Canadian portions, and temperate ecological sub-regions exhibited stronger associations than did more arid sub-regions. Irrigation rates showed no significant influence on population loss. This article focuses on describing the methodological steps, considerations, and benefits of employing this type of machine learning approach to investigating connections between drought and rural population change.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11111-022-00399-9.

Climate Change, Drought, and Potential Environmental Migration Flows Under Different Policy Scenarios

Unmitigated climate change will likely produce major problems for human populations worldwide. Although many researchers and policy-makers believe that drought may be an important “push” factor underlying migration in the future, the precise relationship between drought and migration remains unclear. This article models the potential scope of such movements for the emissions policy choices facing all nation-states today. Applying insights from climate science and computational modeling to migration research, we examine the likely surge of drought-induced migration and assess the prospects of different policy scenarios to mitigate involuntary displacement. Using an ensemble of 16 climate models in conjunction with high-resolution geospatial population data and different policy scenarios, we generate drought projections worldwide and estimate the potential for internal and international population movement due to extreme droughts through the remainder of the 21st century. Our simulations suggest that a potential for drought-induced migration increases by approximately 200 percent under the current international policy scenario (corresponding to the current Paris Agreement targets). In contrast, total migration increases by almost 500 percent, should current international cooperation fail and should unrestricted policies toward greenhouse gas emissions prevail. We argue that despite the continued growth projections of drought-induced migration in all cases, international cooperation on climate change can substantially reduce the global potential for such migration, in contrast to unilateral policy approaches to energy demands. This article highlights the importance of modeling future environmental migrations, in order to manage the pressures and unprecedented policy challenges which are expected to dramatically increase under conditions of unmitigated climate change.

Operationalizing and empirically identifying populations trapped in place by climate and environmental stressors in Mexico

In this paper, we propose a guiding operational definition and corresponding set of empirical steps to identify and study trapped populations. Trapped populations consist of actors who are highly vulnerable to climate and environmental stressors given limited resources (economic, social, etc.), which limit their ability to adapt to these stressors in-situ or by choosing to migrate. Informed by both insights and omissions from prior theoretical and empirical research, we propose a guiding operational definition of trapped populations that appreciates and incorporates actors' limited resources and their migration intentions against the backdrop of climate and environmental stressors. As it should, our operational definition points to a specific set of operations, or steps, which can be followed to empirically identify and study trapped populations. Using data from the Mexican Family Life Survey (MxFLS), we detail the steps permitting both retrospective and prospective identification of trapped populations. We conclude by discussing the strengths and weaknesses of our operational definition and empirical approach, as well as possible extensions.

Demographic perspectives in research on global environmental change

The human population is at the centre of research on global environmental change. On the one hand, population dynamics influence the environment and the global climate system through consumption-based carbon emissions. On the other hand, the health and well-being of the population are already being affected by climate change. A knowledge of population dynamics and population heterogeneity is thus fundamental to improving our understanding of how population size, composition, and distribution influence global environmental change and how these changes affect population subgroups differentially by demographic characteristics and spatial distribution. The increasing relevance of demographic research on the topic, coupled with availability of theoretical concepts and advancement in data and computing facilities, has contributed to growing engagement of demographers in this field. In the past 25 years, demographic research has enriched climate change research-with the key contribution being in moving beyond the narrow view that population matters only in terms of population size-by putting a greater emphasis on population composition and distribution, through presenting both empirical evidence and advanced population forecasting to account for demographic and spatial heterogeneity. What remains missing in the literature is research that investigates how global environmental change affects current and future demographic processes and, consequently, population trends. If global environmental change does influence fertility, mortality, and migration, then population estimates and forecasts need to adjust for climate feedback in population projections. Indisputably, this is the area of new research that directly requires expertise in population science and contribution from demographers.

Environmental Displacement and Mental Well-Being in Banjarnegara, Indonesia

BACKGROUND

Residential moves (displacement) owing to climate- and weather-related disasters may significantly impact mental health. Despite the growing risk from climate change, health impacts of environmental-mobility remain understudied.

OBJECTIVES

We assessed the effects of displacement on the association between landslides and changes in perceived mental well-being in Banjarnegara, Indonesia. We also investigated whether sociodemographics (age, sex, level of education, household-level income, or employment in agriculture) and landslide characteristics (number and severity of landslides) were associated with differing odds of relocation after experiencing landslides.

METHODS

In this cross-sectional study, we surveyed 420 individuals who experienced landslides between 2014 and 2018 to assess perceived changes in mental well-being, comparing after landslide exposure to before landslide exposure. We used a novel six-item measure that was created in collaboration with the local community to compare perceived changes between those who were displaced by landslides and those who were not displaced, using logistic and multinomial regressions adjusted for sociodemographic characteristics. We then assessed whether the odds of displacement differed based on sociodemographic characteristics and landslide exposure characteristics, using logistic regressions.

RESULTS

Those who were displaced were more likely than those who were not displaced to report perceived increases in economic stability [odds ratio (OR)=3.06; 95% confidence interval (CI): 1.45, 6.46], optimism (OR=4.01; 95% CI: 1.87, 8.61), safety (OR=2.71; 95% CI: 1.44, 5.10), religiosity (OR=1.92; 95% CI: 1.03, 3.65), and closeness with community (OR=1.90; 95% CI: 1.10, 3.33) after landslides compared with before their first landslide during the study period. More frequent landslide exposures were associated with reduced odds of relocation, but more severe landslides were associated with increased odds of relocation.

DISCUSSION

These findings suggest that landslides affect the mental well-being not only of those who are displaced but also of those who are left behind. Further, this work supports the need for community-based participatory research to fully capture the health impacts of environmental mobility. https://doi.org/10.1289/EHP9391.

The role of migration and demographic change in small island futures

Low-lying atoll islands are especially threatened by anticipated sea-level rise, and migration is often mentioned as a potential response of these island societies. Further, small island states are developing population, economic and adaptation policies to plan the future. Policies, such as raising of islands or land reclamation, require a long-term vision on populations and migration. However, population and migration systems in small island settings are poorly understood. To address this deficiency requires an approach that considers changing environmental and socio-economic factors and individual migration decision-making. This article introduces the conceptual model of migration and explores migration within one small island nation, the Maldives, as an example. Agent-based simulations of internal migration from 1985–2014 are used as a basis to explore a range of potential demographic futures up to 2050. The simulations consider a set of consistent demographic, environmental, policy and international migration narratives, which describe a range of key uncertainties. The capital island Malé has experienced significant population growth over the last decades, growing from around 67,000 to 153,000 inhabitants from 2000 to 2014, and comprising about 38 percent of the national population in 2014. In all future narratives, which consider possible demographic, governance, environmental and globalization changes, the growth of Malé continues while many other islands are effectively abandoned. The analysis suggests that migration in the Maldives has a strong inertia, and radical change to the environmental and/or socio-economic drivers would be needed for existing trends to change. Findings from this study may have implications for national development and planning for climate change more widely in island nations.

Climate change-induced migration: a bibliometric review

Background

This paper has reviewed the international research on the terms “climate change” and “human migration” from 1999 to 2019. To this end, a bibliometric and a cluster analysis by fractional accounting have been carried out using two of the most important databases: Web of Science (WoS) and Scopus. The research found and studied 140 documents from WoS Core Collection and 193 from Scopus.

Results

The results show a continual increase in the number of articles published and citations received during the whole period studied. The U.S., U.K., Germany and China have been shown to be the most productive countries and there is a predominance of North American organizations supporting and fostering research on these topics.

Conclusions

The main contribution of this article is the analysis of new tendencies. The trend shows a transition from concepts such as vulnerability, climate change, land degradation, refugees and security to others such as concepts such as international migration, climate justice, sustainability, human rights and disaster risk reduction. Future research in this field should address the comparison of results from research focused on human beings to a focus on other living beings.

Introducing Twitter Daily Estimates of Residents and Non-Residents at the County Level

The study of migrations and mobility has historically been severely limited by the absence of reliable data or the temporal sparsity of available data. Using geospatial digital trace data, the study of population movements can be much more precisely and dynamically measured. Our research seeks to develop a near real-time (one-day lag) Twitter census that gives a more temporally granular picture of local and non-local population at the county level. Internal validation reveals over 80% accuracy when compared with users’ self-reported home location. External validation results suggest these stocks correlate with available statistics of residents/non-residents at the county level and can accurately reflect regular (seasonal tourism) and non-regular events such as the Great American Solar Eclipse of 2017. The findings demonstrate that Twitter holds the potential to introduce the dynamic component often lacking in population estimates. This study could potentially benefit various fields such as demography, tourism, emergency management, and public health and create new opportunities for large-scale mobility analyses.

Climate-Induced Migration and Unemployment in Middle-Income Africa

One of the major unresolved questions in the study of vulnerability to climate change is how human migration will respond in low and middle-income countries. The present study directly addresses this lacuna by using census data on migration from 4 million individuals from three middle-income African countries over a 22-year period. We link these individuals to climate exposures in their origins and estimate climatic effects on migration using a fixed-effects regression model. We show that climate anomalies affect mobility in all three countries. Specifically, mobility declines by 19% with a 1-standard deviation increase in temperature in Botswana. Equivalent changes in precipitation cause declines in migration in Botswana (11%) and Kenya (10%), and increases in migration in Zambia (24%). The mechanisms underlying these effects appear to differ by country. Negative associations between precipitation anomalies, unemployment, and inactivity suggest migration declines may be due to an increased local demand for workers to offset production risk, while migration increases may be indicative of new opportunities in destinations. These country-specific findings highlight the contextually-specific nature of climate-migration relationships, and do not support claims that climate change is widely contributing to urbanization across Africa.

The changing climate-migration relationship in China, 1989-2011

A persistent concern about the social consequences of climate change is that large, vulnerable populations will be involuntarily displaced. Existing evidence suggests that changes in precipitation and temperature can increase migration in particular contexts, but the potential for this relationship to evolve over time alongside processes of adaptation and development has not been widely explored. To address this issue, we link longitudinal data from 20 thousand Chinese adults from 1989-2011 to external data on climate anomalies, and use this linked dataset to explore how climatic effects on internal migration have changed over time while controlling for potential spatial and temporal confounders. We find that temperature anomalies initially displaced permanent migrants at the beginning of our study period, but that this effect had reversed by the end of the study period. A parallel analysis of income shares suggests that the explanation might lie in climate vulnerability shifting from agricultural to non-agricultural livelihood activities. Taken together with evidence from previous case studies, our results open the door to a potential future in which development and in-situ adaptation allow climate-induced migration to decline over time, even as climate change unfolds.

Do Social Protection Programs Foster Short-term and Long-term Migration Adaptation Strategies?

We examine how migration is influenced by temperature and precipitation variability, and the extent to which the receipt of a cash transfer affects the use of migration as an adaptation strategy. Climate data is merged with georeferenced panel data (2010-2014) on individual migration collected from the Zambian Child Grant Program (CGP) sites. We use the person-year dataset to identify the direct and heterogeneous causal effects of the CGP on mobility. Having access to cash transfers doubles the rate of male, short-distance moves during cool periods irrespective of wealth. Receipt of cash transfers (among wealthier households) during extreme heat causes an additional retention of males. Cash transfers positively spur long-distance migration under normal climate conditions in the long term. They also facilitate short-distance responses to climate, but not long-distance responses that might be demanded by future climate change.

Usable Science for Managing the Risks of Sea-Level Rise

Sea-level rise sits at the frontier of usable climate climate change research, because it involves natural and human systems with long lags, irreversible losses, and deep uncertainty. For example, many of the measures to adapt to sea-level rise involve infrastructure and land-use decisions, which can have multigenerational lifetimes and will further influence responses in both natural and human systems. Thus, sea-level science has increasingly grappled with the implications of (1) deep uncertainty in future climate system projections, particularly of human emissions and ice sheet dynamics; (2) the overlay of slow trends and high-frequency variability (e.g., tides and storms) that give rise to many of the most relevant impacts; (3) the effects of changing sea level on the physical exposure and vulnerability of ecological and socioeconomic systems; and (4) the challenges of engaging stakeholder communities with the scientific process in a way that genuinely increases the utility of the science for adaptation decision making. Much fundamental climate system research remains to be done, but many of the most critical issues sit at the intersection of natural sciences, social sciences, engineering, decision science, and political economy. Addressing these issues demands a better understanding of the coupled interactions of mean and extreme sea levels, coastal geomorphology, economics, and migration; decision-first approaches that identify and focus research upon those scientific uncertainties most relevant to concrete adaptation choices; and a political economy that allows usable science to become used science.

Migration and Mental Health in the Aftermath of Disaster: Evidence from Mt. Merapi, Indonesia

Migration is a standard survival strategy in the context of disasters. While prior studies have examined factors associated with return migration following disasters, an area that remains relatively underexplored is whether moving home to one's original community results in improved health and well-being compared to other options such as deciding to move on. In the present study, our objective is to explore whether return migration, compared to other migration options, results in superior improvements to mental health. We draw upon data from a cross-sectional pilot study conducted 16 months after a series of volcanic eruptions in Merapi, Indonesia. Using ordinal logistic regression, we find that compared to respondents who were still displaced (reference category), respondents who had "moved home" were proportionally more likely to report good mental health (proportional odds ratios (POR) = 2.02 [95% CI = 1.05, 3.91]) compared to average or poor mental health. Likewise, respondents who had "moved on" were proportionally more likely to report good mental health (POR = 2.64 [95% CI = 0.96, 7.77]. The results suggest that while moving home was an improvement from being displaced, it may have been better to move on, as this yielded superior associations with self-reported mental health.

Climate Change-Induced Migration in Coastal Bangladesh? A Critical Assessment of Migration Drivers in Rural Households under Economic and Environmental Stress

Discussions of climate migration have recognized the need for probabilistic, systematic, and empirical analyses. We examine the importance of environmental stressors in migration using a multi-leveled analysis of a household survey of the climate-stressed rural communities of coastal Bangladesh. We find that a relatively small share (6.5%) of rural coastal people have migrated, overwhelmingly domestically and on a temporary basis. The main motives are better employment opportunities in urban areas, marriage/family reunification, and education. About a third are displaced by flooding that created loss of arable land. Being male, younger, and working outside of agriculture facilitate migration, and also those with greater human and horizontal social capital are more likely to migrate. Exposure to severe river erosion, residing closer to major waterways and in saltwater shrimp farming zones spur migration. Climate migration is in its first instance economic-induced with environmental stress contributing as a secondary factor.

Does It Take a Village? Migration among Rural South African Youth

In a rural African context, the saying, "it takes a village to raise a child," suggests that community characteristics are substantially important in children's lives as they transition to adulthood. Are these contextual factors also related to youth migration? Demographers are uncertain about how community characteristics improve our understanding of an individual's propensity to migrate, beyond individual and household factors. In many low and middle-income country settings, youth become migrants for the first time in their lives to provide access to resources that their families need. We employ discrete-time event history models from the 20032011 Agincourt Health and socio-Demographic Surveillance System in rural South Africa to test whether markers of development in a village are associated with the likelihood of youth and young adults migrating, distinguishing between becoming temporary and permanent migrants during this critical life cycle phase. We find that village characteristics indeed differentially predict migration, but not nearly as substantially as might be expected.

Climate Migration at the Height and End of the Great Mexican Emigration Era

Previous research has linked increasing climate-change-related variability to Mexico-US migration, but only under particular climatic/social conditions and periods of high irregular migration. Using the 2000 and 2010 Mexican censuses, we examine this environment-migration nexus across a broader set of socioecological contexts and during periods of both increasing (1995-1999) and declining (2005-2009) migration. Consistent with the notion that climate can "trap" populations in place, we find that frequent/severe bouts of hot or dry conditions are associated with lower US-bound migration from most of rural Mexico. However, we do find higher climate outmigration during episodes hot and dry climate, or out of places with lower vulnerability. Our comparisons across periods suggest that climate migration is affected by conditions in the U.S. in a similar or slightly weaker manner as other forms of migration are. Altogether, our findings suggest that rural Mexico is unlikely to push large numbers of international "climate refugees" and that climate migration is indeed sensitive to conditions in sending and destination areas.

Trapped in Place? Segmented Resilience to Hurricanes in the Gulf Coast, 1970-2005

Hurricanes pose a continuing hazard to populations in coastal regions. This study estimates the impact of hurricanes on population change in the years 1970-2005 in the U.S. Gulf Coast region. Geophysical models are used to construct a unique data set that simulates the spatial extent and intensity of wind damage and storm surge from the 32 hurricanes that struck the region in this period. Multivariate spatial time-series models are used to estimate the impacts of hurricanes on population change. Population growth is found to be reduced significantly for up to three successive years after counties experience wind damage, particularly at higher levels of damage. Storm surge is associated with reduced population growth in the year after the hurricane. Model extensions show that change in the white and young adult population is more immediately and strongly affected than is change for blacks and elderly residents. Negative effects on population are stronger in counties with lower poverty rates. The differentiated impact of hurricanes on different population groups is interpreted as segmented withdrawal-a form of segmented resilience in which advantaged population groups are more likely to move out of or avoid moving into harm's way while socially vulnerable groups have fewer choices.

Disruption, not displacement: Environmental variability and temporary migration in Bangladesh

Mass migration is one of the most concerning potential outcomes of global climate change. Recent research into environmentally induced migration suggests that relationship is much more complicated than originally posited by the 'environmental refugee' hypothesis. Climate change is likely to increase migration in some cases and reduce it in others, and these movements will more often be temporary and short term than permanent and long term. However, few large-sample studies have examined the evolution of temporary migration under changing environmental conditions. To address this gap, we measure the extent to which temperature, precipitation, and flooding can predict temporary migration in Matlab, Bangladesh. Our analysis incorporates high-frequency demographic surveillance data, a discrete time event history approach, and a range of sociodemographic and contextual controls. This approach reveals that migration declines immediately after flooding but quickly returns to normal. In contrast, optimal precipitation and high temperatures have sustained positive effects on temporary migration that persist over one to two year periods. Building on previous studies of long-term migration, these results challenge the common assumption that flooding, precipitation extremes and high temperatures will consistently increase temporary migration. Instead, our results are consistent with a livelihoods interpretation of environmental migration in which households draw on a range of strategies to cope with environmental variability.

Climate Variability and Inter-Provincial Migration in South America, 1970-2011

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 inter-province 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.

The Environmental Dimensions of Migration

Research on the environmental dimensions of human migration has made important strides in recent years. However, findings have been spread across multiple disciplines with wide ranging methodologies and limited theoretical development. This article reviews key findings of the field and identifies future directions for sociological research. We contend that the field has moved beyond linear environmental "push" theories towards a greater integration of context, including micro-, meso-, and macro-level interactions. We highlight findings that migration is often a household strategy to diversify risk (NELM), interacting with household composition, individual characteristics, social networks, and historical, political and economic contexts. We highlight promising developments in the field, including the recognition that migration is a long-standing form of environmental adaptation and yet only one among many forms of adaptation. Finally, we argue that sociologists could contribute significantly to migration-environment inquiry through attention to issues of inequality, perceptions, and agency vis-à-vis structure.