We know that approximately 1000 tornadoes are observed each year in the United States, but how many tornadoes are observed each year in Europe? As part of my current research project (funded by AXA Research Fund) and trying to provide an answer to this question in order to assess the threat of severe convective storms (those producing tornadoes, large hail, severe wind gusts and lightning) over Europe.
Tornado databases are maintained by few European countries and thus is difficult to evaluate the number of tornadoes that occur each year in Europe. Recently, a new pan-European tornado database has become available that will allow a step-change in our ability to observe and understand tornadoes in Europe. Thus, in my research I am using tornado data from the European Severe Weather Database (ESWD), a unique database of severe-weather maintained by European Severe Storm Laboratory (ESSL). The ESWD is a joint effort between National Meteorological and Hydrological Services and voluntary observers. Also, the public can contribute with observations (submitting a severe weather report to ESWD is very easy and it takes around 5 min. and you can make a contribution to science).
Based on the data from ESWD, 2338 tornadoes were reported between 1 January 2004 and 31 December 2013 in Europe (EU countries and Norway, Belarus, Ukraine, Moldova, Serbia, Bosnia and Herzegovina, Cyprus and Turkey). Thus, approximately 233 tornadoes are observed each year in Europe.
Next, we can ask what is the spatial distribution of tornadoes in Europe? To answer this question, I have plotted the annual average number of tornado per square kilometre at NUTS 3 level for EU countries and at the national level for non-EU countries (Fig. 1). Thus, most of the tornadoes are reported over Northern and Central Europe.
The spatial distribution of tornadoes in Fig. 1 depends not only on the meteorological factors associated with the tornado occurrence (e.g., Markowski and Richardson 2014) but also on non-meteorological factors like the population density. Figure 2 shows the average population density between 2004 and 2013 for Europe based on the data from EUROSTAT.
The high population density over Northern and Central Europe, Italy or United Kingdom may result in more tornadoes begin reported since more people are living in those areas. Thus, there is a population influence on tornado reports in Europe. In my next post I will discuss this influence and how to account for the population bias.