Researchers at the European Severe Storms Laboratory (ESSL), Munich Re, the Ludwig-Maximilians University Munich (LMU) and the German Aerospace Centre (DLR) could show that the number of thunderstorms and the frequency of large hail events have significantly increased in central Europe during past three and a half decades.
A new statistical method (AR-CHaMo) was developed which allows to predict probabilities of local severe convective hazard occurrence (e.g. hail, severe wind gusts or tornadoes) based on large-scale observational data (reanalysis data). Severe convective hazards are local and small-scale phenomena and can therefore not be resolved by common meteorological variables and sizes used in weather or climate models. With AR-CHaMo, the probability of thunderstorm initiation and severe weather occurrence can be determined as a function of parameters such as instability, moisture and wind shear. The method was evaluated using severe weather observations from ESSL’s European Severe Weather Database (ESWD) and EUCLID lightning measurements.
The application of AR-CHaMo to reanalysis data from the European Centre for Medium-Range Weather Forecasts for the time period 1979 to 2016 yielded a significant increase in thunderstorm occurrence, large hail and severe wind events. As an example, the map below shows the trends for severe weather events with hail of 2 cm or larger, according to ERA-Interim and the AR-CHaMo model.
Rädler, A.T., P. Groenemeijer, E. Faust, and R. Sausen, 2018: Detecting Severe Weather Trends Using an Additive Regressive Convective Hazard Model (AR-CHaMo). J. Appl. Meteor. Climatol., 57, 569–587, https://doi.org/10.1175/JAMC-D-17-0132.1