Friday, July 24, 2020

Our Recent Research on Human Migration Networks, Climate Change, and Covid-19

The New York Times yesterday published an article, "The Great Climate Migration,"  which stated: As with much modeling work, the point here is not to provide concrete numerical predictions so much as it is to provide glimpses into possible futures. Human movement is notoriously hard to model.

I have been working on the modeling for human migration networks for over 20 years and, in the past year, with collaborators, I have returned to this important topic. Our research was motivated by real-world events. According to the United Nations Department of Economic and Social Affairs, Population Division, by the end of 2019 the number of people forcibly displaced due to war, conflict, persecution, human rights violations, poverty and economic inequality but also climate change and natural disasters, had grown to 79.5 million. Furthermore, the vulnerability of millions of international migrants may be exacerbated in crisis situations, as actually is the case now with the COVID-19, and, of course, by climate change.

In addition,  migration interactions will be the key to achieving the 2030 Sustainable Development Goals (SDGs) adopted by the member states of the United Nations. In the 2030 Agenda, 9 out of the 17 goals contain targets and indicators that are related to migration or mobility.

In the series of papers, we first set out to include the impacts of regulations on migratory flows and utilities, and took the perspective of migrants behaving in a user-optimizing manner, that is, choosing their locations, subject to the differential between the destination location utility and that in the origin location minus the migration cost. This led us to publishing the paper, "International human migration networks under regulations,"  in the European Journal of Operational Research:

This paper we then extended to include multiple paths between origin and destination nodes, with each path possibly consisting of multiple links. The paper, "Refugee migration networks and regulations: A multiclass, multipath variational inequality framework," was published in the Journal of Global Optimization:

We also introduced, for the first time, a system-optimized perspective for human migration, in which a central authority allocates migrants to locations in a way that is optimal from a societal perspective. In the paper, published in the International Transactions in Operational Research (ITOR):  "Human migration networks and policy interventions: Bringing population distributions in line with system optimization," we demonstrated how, through policy interventions, in the form of subsidies, a governmental body could ensure that, once imposed the migratory flows (and associated population distributions) would generate a system optimum, although migrants were behaving in a user-optimizing manner.  Those of you well-versed in transportation science can see the analogues.

Subsequently, we included capacities associated with the population locations of the multiclass migrants in the paper, "Capacitated human migration networks and subsidization." The paper has been accepted in the volume:  Dynamics of Disasters - Impact, Risk, Resilience, and Solutions, I.S. Kotsireas, A. Nagurney, and P.M. Pardalos, Editors, Springer International Publishing Switzerland, 2020. This paper shows that the results for the  policy interventions in ITOR also hold in the capacitated case.

And, in our most recent paper on human migration, "A system-optimization model for multiclass human migration with migration costs and regulations in the Covid-19 pandemic," also co-authored with Professor Patrizia Daniele of the University of Catania in Italy and her PhD student, Giorgia Cappello, we proposed novel utility functions associated with origin an destination nodes and also considered regulations as in the above work. The COVID-19 pandemic has dramatically  affected global mobility in the form of blockages, restrictions, and travel disruptions, as risk mitigation measures are being implemented by numerous countries. Indeed, the International Organization for Migration (IOM) reports that between 11 March 2020, when the World Health Organization (WHO) declared COVID-19 a pandemic, and 20 April 2020, the total number of movement restrictions implemented around the world has increased to more than 48,000! This paper is now under review in a special issues of a journal.

People since time immemorial have sought to identify better locations for themselves and their families. As The New York Times also noted,  our model offers something far more potentially valuable to policymakers: a detailed look at the staggering human suffering that will be inflicted if countries shut their doors.

Research on human migration networks will continue.