Assessment of urban human mobility perturbation under extreme weather events: A case study in Nanjing, China

Abstract

Extreme weather events (EWEs), due to their high uncertainty, massive scale, irreversibility and destructiveness, may significantly impact cities, including causing notable perturbation to urban human mobility. Recent research has substantially advanced the knowledge on general human mobility patterns in cities, primarily about the spatiotemporal characteristics of trajectories of urban population, but has rarely examined the perturbation of these mobility patterns during EWEs. To quantitatively assess human mobility perturbation, this study proposes to measure both the instantaneous perturbation at any given moment during an EWE, and the accumulated perturbation over the entire timespan of the EWE. Using two metrics that are developed for the above purpose, a case study is conducted in Nanjing, a major city in China, which recently experienced record-breaking rainstorm and snowstorm events. Based on trajectories of all taxies and buses in Nanjing during these events, the case study quantitatively assesses the perturbation of human mobility in the city, compares it between two EWEs and between two modes of transport, and analyzes the geographical distribution of the perturbation within the city boundary. Based on the results, further insights into the impacts of EWEs on urban human mobility are discussed in the paper.