A thunderstorm climatology of Romania (1941―2022)

Thunderstorms and their associated hazards pose a significant threat to society and the economy. In Europe, between 1980 and 2022, thunderstorms caused an estimated EUR 190 billion in economic losses. In Romania, the rate of cloud-to- ground (CG) lightning fatality is one of the highest in Europe. This study aims to reevaluate the risk of lightning in Romania by updating the CG lightning climatol- ogy for the period 2010–2022 and analysing long-term changes (1941-2022) in the frequency of thunderstorm environments. Data were obtained from the Arrival Time Difference Lightning Network (ATDnet) and the ERA5 reanalysis. On average, ap- proximately 760,000 flashes occurred each year in Romania during the study period, with a maximum mean annual flash density of approximately 6.5 flashes km−2 yr−1 over the Southern Carpathians. Approximately 75% of all flashes were detected in June–August, with a peak in the afternoon hours. There is a general decrease in flash density in Romania, but this trend is statistically significant only in western Romania. The highest number of hours with thunderstorm environments (270–390 hours yr−1) was predominantly observed in the mountainous regions of central and western Ro- mania. There is a significant increase in the number of hours with thunderstorms per decade, especially in eastern and southern Romania (>4 hours per decade). The re- sults of this study allow for a better understanding of the risk posed by CG lightning in Romania, improved forecasting of thunderstorms, and serve as a basis for developing mitigation strategies to reduce the impact of CG lightning.