The interdependence of weather and human behavior is critical for understanding their mutual impacts and the broader implications of climate change on daily life. In this study, we introduce the Human Mobility Perturbation Index (HMPI) to quantify the degree of influence on human mobility caused by external factors, with a primary focus on rainfall and a brief illustrative example of an earthquake. HMPI is derived from nationwide DOCOMO Mobile Spatial Statistics (MSS) data for all of Japan during June and July 2018, encompassing a typhoon passage, an extreme heavy rain condition in Western Japan, and the Osaka earthquake. HMPI is then spatially and temporally matched with radar-rain-gauge analyzed precipitation data provided by Japan Meteorological Agency (JMA) to investigate rainfall’s influence on HMPI. Since MSS provides hourly population estimates on a 500 m × 500 m grid, we can focus only on residential mobility to avoid the redundancy of tracking both trip origins and destinations. Deviations of HMPI from a zero baseline indicate the severity of perturbation. Negative HMPI values represent reduced mobility, while positive values represent increased mobility. Cross-correlation of HMPI with rain intensity shows high correlation and indicates the population’s delayed response to rainfall in most prefectures which experience higher rain intensity. Linear regression of daily averaged HMPI and rain intensity further confirm that HMPI effectively captures heavy-rainfall-induced mobility reduction, with increasing rain intensity corresponding to lower HMPI values. This study confirms and quantifies the influence of rainfall on human mobility. The intensity and timing of these behavioral responses differ across prefectures in Japan.
Yoongsomporn et al. (Thu,) studied this question.