  Diversity of physical encounters and social interactions in urban
environments are known to spur economic productivity and innovation in cities,
while also to foster social capital and resilience of communities. However,
mobility restrictions during the pandemic have forced people to substantially
reduce urban physical encounters, raising questions on the social implications
of such behavioral changes. In this paper, we study how the income diversity of
urban encounters have changed during different periods throughout the pandemic,
using a large-scale, privacy-enhanced mobility dataset of more than one million
anonymized mobile phone users in four large US cities, collected across three
years spanning before and during the pandemic. We find that the diversity of
urban encounters have substantially decreased (by 15% to 30%) during the
pandemic and has persisted through late 2021, even though aggregated mobility
metrics have recovered to pre-pandemic levels. Counterfactual analyses show
that while the reduction of outside activities (higher rates of staying at
home) was a major factor that contributed to decreased diversity in the early
stages of the pandemic, behavioral changes including lower willingness to
explore new places and changes in visitation preferences further worsened the
long-term diversity of encounters. Our findings suggest that the pandemic could
have long-lasting negative effects on urban income diversity, and provide
implications for managing the trade-off between the stringency of COVID-19
policies and the diversity of urban encounters as we move beyond the pandemic.
