Resilience Patterns of Human Mobility during Extreme Urban Floods Unveiled by New Study

Resilience can be explained as the overall ability of a system to prepare for, absorb, and recover from external or internal perturbations and shocks. In the context of human mobility, resilience refers to the ability of people’s movements within and between cities to handle and adapt to disruptive events, such as natural disasters.

On July 20, 2021, record-breaking rain fell in Zhengzhou District, Henan Province, China, a densely populated inland area with a total area of ​​7,600 km2.², 12.7 million residents, and the urbanization rate is 79.1%. The region is located in a semi-arid region and is known for its relatively low average annual rainfall.

Unexpectedly heavy rainfall led to severe flooding in urban areas, causing massive injuries to the public and losses to critical infrastructure systems, with 380 deaths; Nearly two million people were affected. Very quickly, this horrific event in central China drew widespread attention worldwide.

Using 1.32 billion mobile phone signal records generated by 4.35 million people during the Zhengzhou “720” flood event, researchers from Peking University, Henan University, and China’s National Geomatics Key Center analyzed how people’s mobility responded to the severe urban flood disaster during the 2021 summer.

said Professor Pengjun Zhao, lead author of the study and dean of the School of Urban Planning and Design of Peking University.

Who is most vulnerable to the impact of this flood?

By grouping data based on the gender and age of the traveler, the study found that there were significant differences in movement flexibility in the different groups, with females and adolescents under 18 years of age and elderly people over 60 years of age showing relatively less flexibility and therefore more grasping. likely to be affected by floods.

The study highlights the importance of considering demographic data in disaster planning and response efforts, as specific groups may require targeted support and resources to effectively mitigate the impact of disasters.

“The result demonstrates quantitatively that the probability of maintaining the usual rate of travel in these population groups is much lower than in other groups during the event, which explains their low level of resilience and insufficient recovery,” said Professor Zhao.

Unexpected flexibility patterns in human mobility

In addition, by analyzing changes in mobility at various geographic scales, the study revealed four distinct patterns of human mobility. Among these patterns, three abnormalities were found, namely the ‘inverted bathtub curve’, the ‘continuously decreasing curve’, and the ‘continuously increasing curve’. Together, these abnormal patterns account for about 50% of the total area.

These abnormal resilience patterns indicate unusual mass mobility behaviors in response to this extreme catastrophe. “Taking inflow as an example, the inverted bathtub pattern confirms that this flood disaster stimulates inflow motion rather than suppressing it in those places,” said Dr. Junqing Tang, first author of this study and assistant professor in the College of Urban Planning. and design.

“Meanwhile, in the recovery phase, the elevated mobility flow dissipates to a lower level. This may reflect disaster avoidance behaviors in which people temporarily change their travel route choices to cluster in certain new areas during a flood, but after the event, shift back to their usual routes.”

Are these patterns of abnormal flexibility related to traveler characteristics?

The research team also explored the relationship between heterogeneous flexibility patterns and traveler gender and age traits. The results indicate that normal and abnormal locomotor flexibility patterns are not primarily associated with sex or age.

This particular finding indicates that on a collective scale whether dynamic human movements in response to urban flooding follow a normal or abnormal pattern of resilience that cannot be explained by gender or age traits, suggests a universal behavioral mechanism for disaster avoidance responses across populations.

Given the common association between travel behaviors and traveler sociodemographic characteristics, the evidence here provides a potential ‘nudge’ for the investigation of unusual human mobility during flood emergencies.

The study has been published in the journal National Science Review.