Experiences with >50,000 Crowdsourced Hail Reports in Switzerland

Barras, Hélène; Hering, Alessandro; Martynov, Andrey; Noti, Pascal-Andreas; Germann, Urs; Martius, Olivia (2019). Experiences with >50,000 Crowdsourced Hail Reports in Switzerland. Bulletin of the American Meteorological Society, 100(8), pp. 1429-1440. American Meteorological Society 10.1175/BAMS-D-18-0090.1

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Crowdsourcing is an observational method that has gained increasing popularity in recent years. In hail research, crowdsourced reports bridge the gap between heuristically defined radar hail algorithms, which are automatic and spatially and temporally widespread, and hail sensors, which provide precise hail measurements at fewer locations. We report on experiences with and first results from a hail size reporting function in the app of the Swiss National Weather Service. App users can report the presence and size of hail by choosing a predefined size category. Since May 2015, the app has gathered >50,000 hail reports from the Swiss population. This is an unprecedented wealth of data on the presence and approximate size of hail on the ground. The reports are filtered automatically for plausibility. The filters require a minimum radar reflectivity value in a neighborhood of a report, remove duplicate reports and obviously artificial patterns, and limit the time difference between the event and the report submission time. Except for the largest size category, the filters seem to be successful. After filtering, 48% of all reports remain, which we compare against two operationally used radar hail detection and size estimation algorithms, probability of hail (POH) and maximum expected severe hail size (MESHS). The comparison suggests that POH and MESHS are defined too restrictively and that some hail events are missed by the algorithms. Although there is significant variability between size categories, we found a positive correlation between the reported hail size and the radar-based size estimates.

Item Type:

Journal Article (Original Article)


10 Strategic Research Centers > Oeschger Centre for Climate Change Research (OCCR) > MobiLab
08 Faculty of Science > Institute of Geography > Physical Geography > Unit Impact
10 Strategic Research Centers > Oeschger Centre for Climate Change Research (OCCR)
08 Faculty of Science > Institute of Geography
08 Faculty of Science > Institute of Geography > Physical Geography

UniBE Contributor:

Barras, Hélène Christine Louise, Martynov, Andrey, Romppainen-Martius, Olivia


500 Science > 550 Earth sciences & geology
900 History > 910 Geography & travel




American Meteorological Society


[245] Mobiliar Lab für Naturrisiken Official URL




Hélène Christine Louise Barras

Date Deposited:

18 Sep 2019 15:03

Last Modified:

16 Feb 2023 09:54

Publisher DOI:






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