A global database on holdover time of lightning-ignited wildfires

Abstract

Abstract. Holdover fires are usually associated with lightning-ignited wildfires (LIWs), which can experience a smoldering phase or go undetected for several hours, days or even weeks before being reported. Since the existence and duration of the smoldering combustion in LIWs is usually unknown, holdover time is conventionally defined as the time between the lightning event that ignited the fire and the time the fire is detected. Therefore, all LIWs have an associated holdover time, which may range from a few minutes to several days. However, we lack a comprehensive understanding of holdover times. Here, we introduce a global database on holdover times of LIWs. We have collected holdover time data from 29 different studies across the world through a literature review and datasets assembled by authors of the original studies. The database is composed of three data files (censored data, non-censored data, ancillary data) and three metadata files (description of database variables, list of references, reproducible examples). Censored data are the core of the database and consist of different frequency distributions reporting the number or relative frequency of LIWs per interval of holdover time. In addition, ancillary data provide further information to understand the methods and contexts in which the data were generated in the original studies. The first version of the database contains 42 frequency distributions of holdover time built with data on more than 152 375 LIWs from 13 countries in five continents covering a time span from 1921 to 2020. This database is the first freely available, harmonized and ready-to-use global source of holdover time data, which may be used in different ways to investigate LIWs and model the holdover phenomenon. The complete database can be downloaded at https://doi.org/10.5281/zenodo.7352172 (Moris et al., 2022).

Comparing ground-based lightning detection networks near wildfire points-of-origin

“…The second, more-strict approach, applied a simple quality-control filter to remove strokes between −10 kA and 10 kA because these weaker IC strokes can be mis-classified as CG lightning (Abatzoglou et al 2016;Schultz et al 2019). The more-strict approach reduced the holdover time to three days before the fire report date as the majority of lightning fires are observed within this period (Schultz et al 2019;Moris et al 2023), and this is a common period during which operational forecasters have access to lightning data. For both comparisons, we also counted CG lightning strokes in the day after the reported discovery date to account for potentially misreported dates (Schultz et al 2019).…”

“…In fire-prone environments, lightning detection informs wildfire managers about the potential for ignitions (Schultz et al 2019). Lightning-ignited wildfires are an important component of the natural fire cycle in the western United States (wUS) and worldwide (Moris et al 2023). In the wUS, lightning-ignited wildfires are associated with approximately 69% of burned area (Abatzoglou et al 2016).…”

On the Role of Continuing Currents in Lightning‐Induced Fire Ignition

“…For these reasons, we used the proximity index A proposed by Larjavaara et al. (2005) to search for the most probable lightning candidates and to find the parent thunderstorm of each fire, $$$A=\left(1-\frac{T}{{T}_{\max }}\right)\times \left(1-\frac{D}{{D}_{\max }}\right),$$$ where D is the distance between the reported fire location and the lightning flash or group, and T is the time between fire ignition and detection, also known as holdover time (Moris et al., 2023; Wotton & Martell, 2005). Parameters ( T max ) and ( D max ) correspond to the maximum holdover time and distance between a fire and a lightning discharge to consider the latter as the potential cause of ignition.…”

“…where D is the distance between the reported fire location and the lightning flash or group, and T is the time between fire ignition and detection, also known as holdover time (Moris et al, 2023;Wotton & Martell, 2005).…”

“…The survival and arrival phases account for the emergence and spread of the fire, which are determined by the meteorological conditions and the fuel availability and moisture. Wildfires ignited by lightning are reported only when the arrival phase is reached and they become detectable by local fire alarm/monitoring systems or satellite‐based instruments (Justice et al., 2002; Moris et al., 2023). Therefore, research focused on the ignition phase is scarce.…”