Abstract
Abstract. Understanding city residents' collective geotagged behaviors (CGTBs) in response to hazards and emergency events is important in disaster mitigation and emergency response. It is a challenge, if not impossible, to directly observe CGTBs during a real-time matter. This study used the number of location requests (NLR) data generated by smartphone users for a variety of purposes such as map navigation, car hailing, and food delivery to infer the dynamics of CGTBs in response to rainstorms in eight Chinese cities. We examined rainstorms, flooding, and NLR anomalies, as well as the associations among them, in eight selected cities across mainland China. The time series NLR clearly reflects cities' general diurnal rhythm, and the total NLR is moderately correlated with the total city population. Anomalies of the NLR were identified at both the city and grid scale using the Seasonal Hybrid Extreme Studentized Deviate (S-H-ESD) method. Analysis results demonstrated that the NLR anomalies at the city and grid levels are well associated with rainstorms, indicating that city residents request more location-based services (e.g., map navigation, car hailing, food delivery, etc.) when there is a rainstorm. However, the sensitivity of the city residents' collective geotagged behaviors in response to rainstorms varies in different cities as shown by different peak rainfall intensity thresholds. Significant high peak rainfall intensity tends to trigger city flooding, which leads to increased location-based requests as shown by positive anomalies in the time series NLR.
Highlights
Global climate change is making rainfall events heavier and more frequent in many areas
This study explored the urban anomalies and their variations in response to rainstorms using the number of location requests (NLR) from smartphone users
This study shows the potential of the NLR data to reflect city residents’ collective geotagged behaviors
Summary
Global climate change is making rainfall events heavier and more frequent in many areas. Inundation of cities’ critical infrastructure and populated communities tends to disrupt urban residents’ social and economic activities and even cause dramatic loss of life and property (Papagiannaki et al, 2013; Spitalar et al, 2014; Liao et al, 2019). According to the released survey in the Bulletin of Flood and Drought Disasters in China, more than 104 cities were struck by floods in 2017, affecting a population of up to 2.18 million and causing over USD 2.46 billion in direct economic losses (China National Climate Center, 2017). The impacts of a rainstorm are usually evaluated with respect to the interactions among rainfall intensity, population exposure, urban vulnerability, and the society coping capacity (Spitalar et al, 2014; Papagiannaki et al, 2017). Nowadays the peak rainfall intensity is widely used to determine the critical rainfall threshold for issuing flash flood warnings (Cannon et al, 2007; Diakakis, 2012; Miao et al, 2016)
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