Milling time and public perception of Cell Broadcast tsunami alerts tested on the French Mediterranean coast on 19 January 2024[Base de données sur les délais de préparation et la perception d'une alerte tsunami envoyée par diffusion cellulaire lors du test du 19 janvier 2024 le long du littoral méditerranéen français]

There is limited research on public perception, intended responses and message understanding in the situation of Cell Broadcast mobile alerts, especially in France as the Cell Broadcast has been recently developed (since June 2022). This original dataset has been completed during a tsunami trial conducted on 19 January 2024, by using an online questionnaire, with a short URL link directly included in mobile alert messages, displayed along the French Mediterranean coast (with 189 municipalities and 9 departments). The aim is to further evaluate what people do and think upon receiving Cell Broadcast alerts, that deliver an attention-grabbing message directly on the screen of mobile phones of people located in the at-risk zones. The Tsunami Evacuation Zones (TEZ) have been designed as the Cell Broadcast zone, by considering at fine scale all the areas characterized by a height of 0 to 5m above sea level and up to 200m inside river mouths. A first notification was sent in the TEZ from 09:30 to 10:30, and a second from 10:35 to 10:50 to close the test. A total of 9,446 totally-completed answers have been collected during 2 days even if 82.9% (n=7,825 answers) were already collected at 11:00. The sample consists of 24 questions, designed by an interdisciplinary research team (including geographers, designers and psychologists researchers), to respond to a dual challenge: 1) firstly, to evaluate the participants' immediate reactions to the Cell Broadcast messages, displayed with sound tone (that may provoke anxiety, fear or stress, particularly if individuals are confused by such type of alert), and 2) second, to estimate the intended milling time (i.e., the time one person declared before he decides to evacuate) and to measure its influence for evacuation planning. Other variables (age, professional status, location during alert reception) completed the dataset and can be used as socio-demographic parameters as well as explanatory variables in case of more complete statistical analyses. The 9 Prefectures, the French Ministry of Interior and the researchers team were involved before the test (to produce the Tsunami Evacuation Zones and to design the alert messages), during the test (to observe reactions of recipients, but only at local scales) and after the test (to present results to the practitioners and disseminate the scientific lessons that can be addressed with this questionnaire). This original dataset serves as a critical resource for researchers, policymakers, and emergency managers focused on optimizing Cell Broadcast alerts and defining alert messages. It is particularly suited to enhance the effectiveness and understanding of tsunami Cell Broadcast alerts.