Lightning is the most important ignition source of natural wildfires worldwide. Lightning-ignited wildfires are an important component of the fire regime in remote and mountainous regions along the globe, such as the boreal forests of Alaska, Canada and Siberia. Despite lightning fires are much less frequent than human-caused fires in many regions, natural fires can still be an essential component of the summer fire regime (e.g., the western USA and the Alps) and extreme fire seasons (e.g., Australia and Spain).
The holdover phenomenon is a particular characteristic of some lightning fires. Lightning fires may present a survival phase between the ignition and discovery of the fire. This phase is sometimes known as holdover or smouldering phase, and is characterized by the smoldering combustion (i.e., slow, low-temperature, flameless burning) of the soil organic layers surrounding the base of the tree hit by the lightning strike. Given that the existence and duration of the survival phase of lightning fires is unknown in almost all the cases, holdover time is simply defined as the time between lightning-induced fire ignition and fire detection.
In order to improve our limited understanding on the initial behavior of lightning fires, a database on holdover times was built by an international and interdisciplinary group of researchers interested in lightning fires. The database is freely available from the open repository Zenodo, and is part of the research project FIRESKY (Fire from the sky: understanding lightning fires in the Pyrocene), supported by a postdoctoral fellowship funded by the government of Asturias (Spain). A complete description of the database has been published in the journal Earth System Science Data.
The first version of the database contains 42 frequency distributions of holdover time built with data collected from 29 different studies and more than 152,375 lightning fires. The data come from 13 countries in five continents: North America (United States and Canada), South America (Brazil), Europe (Spain, Italy, Switzerland, Austria, France, Portugal, Greece and Finland), Asia (Russia) and Oceania (Australia), covering a time span of a century (from 1921 to 2020). The data are harmonized and ready to be used in different ways to investigate and model lightning fires.
Moris JV, Álvarez-Álvarez P, Conedera M, Dorph A, Hessilt TD, Hunt HGP, Libonati R, Menezes LS, Müller MM, Pérez-Invernón FJ, Pezzatti GB, Pineda N, Scholten RC, Veraverbeke S, Wotton BM, Ascoli D. 2022. Database on holdover time of lightning-ignited wildfires. Zenodo [Dataset]. https://doi.org/10.5281/zenodo.7352172
Moris JV, Álvarez-Álvarez P, Conedera M, Dorph A, Hessilt TD, Hunt HGP, Libonati R, Menezes LS, Müller MM, Pérez-Invernón FJ, Pezzatti GB, Pineda N, Scholten RC, Veraverbeke S, Wotton BM, Ascoli D. 2023. A global database on holdover time of lightning-ignited wildfires. Earth System Science Data 15: 1151-1163. https://doi.org/10.5194/essd-15-1151-2023