Thunderstorm hazards include lightning, heavy rainfall, hail, thunder-snow, strong winds and tornadoes. This hazardous weather can cause flooding; damage to property, infrastructure and crops; disrupt transport and outdoor maintenance; cause injury; and pose a risk to life. Thunderstorm climatologies provide valuable information for decision-makers, the public and experts on how to reduce the risk of exposure to thunderstorm hazards. Information on the spatio-temporal distributions of lightning and thunderstorms as well as their characteristics such as direction of travel, duration and intensity helps avoid unnecessary exposure to thunderstorm hazards. However, as there are such a wide variety of reasons that this information might be required, for example scheduling drain clearance for heavy rains; hikers avoiding high-risk areas once a thunderstorm has formed; and avoiding scheduling wind farm maintenance at times when there is an increased risk of lightning, it is difficult to provide general information on distributions using one approach. This research explores a) the different datasets available, b) the spatio-temporal distributions of thunderstorms and lightning using a lightning climatology approach, c) the spatio-temporal distributions and characteristics of thunderstorms and their movement using a thunderstorm tracking approach, and d) the effect of topography on these distributions and characteristics through combining lightning climatology with thunderstorm tracking. The varied approaches provide high-resolution information that is to be made available on an open-access basis for numerous end users. Key findings include a) the benefit of using multiple lightning location systems’ lightning flash data to establish potential areas of uncertainty in a lightning climatology. This approach identifies where there is a difference between the datasets and therefore where they may reflect dataset temporal/spatial inhomogeneity rather than a real change in lightning distribution. b) The lightning climatology identified seven regions within the UK and Ireland where there is a distinct temporal distribution of lightning, providing regional level information to assist people in scheduling high-risk outdoor activities at low-risk times. c) Thunderstorm tracking using lightning flash data produced a dataset of thunderstorms (with at least 3 lightning flashes) occurring between 2008 and 2018 inclusive. This dataset includes thunderstorm characteristics such as a shapefile of thunderstorm area, start/stop date and time, duration, distance travelled, bearing (direction) of travel, and lightning flash intensity. This provides information on thunderstorm behaviour and severity as well as differentiating between thunderstorm initiation points and their probable tracks and therefore, higher risk areas, once formed. Lastly, d) both lightning climatology and thunderstorm track data were applied to four case study areas with varied elevation profiles to provide detailed information on how thunderstorms behave around topographic features. This shows that the response of lightning and thunderstorm density varies between different case study regions of the UK, as well as being variable within case study regions themselves. This supports the compilation of regional specific data for topographic areas to help outdoor users avoid exposure to these hazards. Employing both lightning climatology and thunderstorm track methods gains insight into the extent of these hazards (thunderstorm severity/duration) alongside thunderstorm density and flash density information which provides further information on why distributions between regions may vary. This can be important because the user may wish to know for example, whether the increased flash density in a region is the result of frequent low flash thunderstorms or infrequent severe thunderstorms. It is, therefore recommended that future work, where possible, includes multiple datasets and approaches to gain a full understanding of both the implications and limitations of the findings.
Thunderstorm and Lightning Climatologies of the UK, Ireland and Northwest Europe: Employing Multiple Datasets and Methodologies to Improve Understanding of and Mitigate Exposure to Storm Hazards
Hayward, L. E. (Author). 29 Aug 2023
Student thesis: Doctoral Thesis