The form and evolution of international migration networks, 1990-2015.

Presently, there is no agreed upon data-driven approach for identifying the geographic boundaries of migration networks that international migration systems are ultimately manifested in. Drawing from research on community detection methods, we introduce and apply the Information Theoretic Community Detection Algorithm for identifying and studying the geographic boundaries of migration networks. Using a new set of estimates of country-to-country migration flows every 5 years from 1990 to 1995 to 2010-2015, we trace the form and evolution of international migration networks over the past 25 years. Consistent with the concept of dynamic stability, we show that the number, size and internal country compositions of international migration networks have been remarkably stable over time; however, we also document many short-term fluctuations. We conclude by reflecting on the spirit of our work in this paper, which is to promote consensus around tools and best practices for identifying and studying international migration networks.

Evacuees and Migrants Exhibit Different Migration Systems After the Great East Japan Earthquake and Tsunami.

Research on the destinations of environmentally induced migrants has found simultaneous migration to both nearby and long-distance destinations, most likely caused by the comingling of evacuee and permanent migrant data. Using a unique data set of separate evacuee and migration destinations, we compare and contrast the pre-, peri-, and post-disaster migration systems of permanent migrants and temporary evacuees of the Great East Japan Earthquake and Tsunami. We construct and compare prefecture-to-prefecture migration matrices for Japanese prefectures to investigate the similarity of migration systems. We find evidence supporting the presence of two separate migration systems-one for evacuees, who seem to emphasize short distance migration, and one for more permanent migrants, who emphasize migration to destinations with preexisting ties. Additionally, our results show that permanent migration in the peri- and post-periods is largely identical to the preexisting migration system. Our results demonstrate stability in migration systems concerning migration after a major environmental event.

Population recovery in New Orleans after Hurricane Katrina: Exploring the potential role of stage migration in migration systems.

In this research brief, we explore how places affected by natural disasters recover their populations through indirect, or "stage," migration. Specifically, we consider the idea that post-disaster impediments (e.g., housing and property damage) in disaster-affected areas spawn migration flows toward and, over time, to disaster-affected areas through intermediary destinations. Taking as our case Orleans Parish over a five-year period after Hurricane Katrina, we show that stage migration accounted for up to about one-fourth of population recovery. We close by discussing the implications, limitations, and potential extensions of our work.

Recovery Migration to the City of New Orleans after Hurricane Katrina: A Migration Systems Approach.

Hurricane Katrina's effect on the population of the City of New Orleans provides a model of how severe weather events, which are likely to increase in frequency and strength as the climate warms, might affect other large coastal cities. Our research focuses on changes in the migration system - defined as the system of ties between Orleans Parish and all other U.S. counties - between the pre-disaster (1999-2004) and recovery (2007-2009) periods. Using Internal Revenue Service county-to-county migration flow data, we find that in the recovery period Orleans Parish increased the number of migration ties with and received larger migration flows from nearby counties in the Gulf of Mexico coastal region, thereby spatially concentrating and intensifying the in-migration dimension of this predominantly urban system, while the out-migration dimension contracted and had smaller flows. We interpret these changes as the migration system relying on its strongest ties to nearby and less damaged counties to generate recovery in-migration.