A reassessment of the history of the temporal resolution of rainfall data at the global scale

• Available rainfall data are characterized by different time resolution, “ta” • An updated database involving metadata from many geographic areas is presented. • The “ta” history of rainfall data in a variety of rain gauges is reconstructed. • The registration methods of the rainfall data changed over the years. • Currently about 50% of the stations provide rainfall data at any time-resolution. The availability of rainfall data is of paramount importance in most hydrological studies and is directly dependent on the type of sensors used as well as the recording systems adopted. In fact, these elements have a crucial influence on the temporal resolution (t a ) of stored rainfall data, which in turn affects the types of analysis that can be conducted, making knowledge of t a on a global scale of particular interest to the entire scientific community and also for engineers. For rain gauges installed more than 70–80 years ago the earliest recordings were manual with coarse temporal resolution. Instead, mechanical recordings on paper rolls began in the early decades of the last century, while digital recordings began only in the last four decades, making analyses requiring long time series of sub-hourly rainfall data impossible. This paper presents a significant update of a previous historical analysis of the time-resolution of t a ( Morbidelli et al., 2020 ) by which 126,438 stations, located in 77 different geographical areas, were collected into a database, quintupling the number of stations of the previous database and including areas not considered before. It was found that a high percentage of rain gauge stations currently provides useful data at any time-resolution, but there is an increasing development of rainfall networks characterized by very inexpensive, volunteer-operated stations that acquire one data per day (t a = 1440 min), allowing only limited rainfall-related analyses. The invitation for all rain gauge network operators to contribute additional data to the database remains open.