Quantifying the dynamics of migration after Hurricane Maria in Puerto Rico

Abstract

Population displacement may occur after natural disasters, permanently altering the demographic composition of the affected regions. Measuring this displacement is vital for both optimal postdisaster resource allocation and calculation of measures of public health interest such as mortality estimates. Here, we analyzed data generated by mobile phones and social media to estimate the weekly island-wide population at risk and within-island geographic heterogeneity of migration in Puerto Rico after Hurricane Maria. We compared these two data sources with population estimates derived from air travel records and census data. We observed a loss of population across all data sources throughout the study period; however, the magnitude and dynamics differ by the data source. Census data predict a population loss of just over 129,000 from July 2017 to July 2018, a 4% decrease; air travel data predict a population loss of 168,295 for the same period, a 5% decrease; mobile phone-based estimates predict a loss of 235,375 from July 2017 to May 2018, an 8% decrease; and social media-based estimates predict a loss of 476,779 from August 2017 to August 2018, a 17% decrease. On average, municipalities with a smaller population size lost a bigger proportion of their population. Moreover, we infer that these municipalities experienced greater infrastructure damage as measured by the proportion of unknown locations stemming from these regions. Finally, our analysis measures a general shift of population from rural to urban centers within the island. Passively collected data provide a promising supplement to current at-risk population estimation procedures; however, each data source has its own biases and limitations.

Keywords: Hurricane Maria; Puerto Rico; passively collected data; population displacement.

Fig. 1.

Population estimates for each data source.

Fig. 2.

Small municipalities lost a larger portion of their population compared with large ones. (A) Relative change in the population of Facebook cohort members per municipality. Each curve corresponds to a different municipality. Population size in July 2017 is denoted by color. (B) Average percentage change in population at the end of the study period, relative to baseline, compared with the ACS population size of the municipality at baseline. The geographical regions are presented in SI Appendix, Fig. S5. We fitted a linear model to each population curve and computed the average percentage change using the first and last fitted values. The vertical line corresponds to the day when Hurricane Maria made landfall in Puerto Rico.

Fig. 3.

Immigration of Puerto Rican Facebook (FB) cohort members within and outside of Puerto Rico. (A) Top six municipalities in Puerto Rico in terms of influx of FB cohort members who were located elsewhere before Hurricane Maria. (B) Top five destinations of FB cohort members after Hurricane Maria. The “Others” curve corresponds to the influx of all other destinations together. The vertical lines correspond to the day when Hurricane Maria made landfall in Puerto Rico.

Fig. 4.

Facebook users with unknown locations. (A) Percentage of individuals whose location was unknown by municipality. The vertical line denotes the day Hurricane Maria made landfall. Baseline population size is denoted in color. (B) Percentage of individuals with unknown location relative to San Juan for the week of 2 October 2017, the week after Hurricane Maria. The municipality in white represents Las Marias, the one municipality for which we had no data.