In recent decades, an increase in natural (e.g., floods, hurricanes, droughts) and technological disasters (e.g., hazardous material releases) was observed by many researchers (e.g., Pescaroli et al., 2018; Shen & Nam Hwang, 2019; Sankaran et al., 2022). Such an increment can have significant consequences for millions of people all over the world. Indeed, many natural hazards, including meteorological, hydrological and climatological events, may turn into disasters, causing physical impacts like injuries, casualties, and property damages, but also non-physical effects like psychological, mental, and political wounds (Lindell, 2013; Pescaroli et al., 2018). There is a growing body of literature showing that human injuries, causalities, and economic losses caused by natural hazards have been increasing over the past decades, mostly because of the intensification of human pressure on the natural environment (e.g., O’Keefe et al. 1976; Mileti 1999; Dewan 2013; Kelman, 2020; Hamidifar & Nones, 2023). Therefore, for appropriate disaster management, there is a need for a better understanding of what are the key spatio-temporal scales at which natural hazard impact, and what might be the correlations between such hazards (Pescaroli et al., 2018).
Drought is a climatic hazard that occurs in most world climates and can have considerable economic, societal, and environmental impacts (UNISDR, 2015; Naumann et al., 2018,2021). Drought, like other natural hazards, is driven by climate change and human pressure, but compared to other happenings like floods, events connected to such a phenomenon tend to be longer, sometimes in the order of years. Presently, there is various evidence proving that drought can be a major threat in the future, especially in the form of flash drought (Shah et al., 2022). To adequately tackle the increment of droughts events, recognizable in particular at the regional scale (Dhawale et al., 2022; Shahdad & Saber, 2022), more complex and long-lasting management strategies are needed (Sayers et al., 2017; Hall & Leng, 2019). Like all natural hazards, droughts are multidimensional spatial-temporal events, but they are exceptional because of the diversity of geophysical variables needed to characterize droughts, as well as their consequences, such as wildfires.
Past investigations (Scasta et al., 2016) have shown that, recently, the western United States were affected by an increment in wildfire size, extent, seasonality, and severity, which might relate to more prolonged drought periods driven by climate change. In this work, the authors investigated significant wildfire events that happened in 2003 and 2012, pointing out that such years were characterized by below-average precipitation and negative Palmer Drought Severity Index values (namely, dry conditions). Such a result suggests that wildfires do not act independently of drought, but rather they interact with short-term weather and long-term climatic patterns that change over time.
There has been growing concern about the impact of climate change on wildfire events. For example, Marín et al. (2018) studied the relationship between drought and forest fires in Mexico from 2005–2015. They used georeferenced fire records and a multiscale drought index to identify four fire clusters in the study area, and found that the peak in fire frequency occurred in 2011. Also, they assessed how fire activity related to the drought index for both the entire study period and 2011 specifically. Their study revealed a strong correlation between drought severity and forest fires in Mexico, particularly in the northern and central regions during the dry season. Investigating the temporal dynamics of forest fire in India by means of remote sensing methods, Srivastava & Garg (2013) demonstrated that, in this country, fires are positively correlated with the temperature and the dryness of the forested areas.
However, global warming is not the only cause of an increase in wildfires, as humans are generally the main driver of such events. Focusing on a long-term investigation of wildfire events in the conterminous US, Strader (2018) pointed out that, in the period 1940–2010, wildfire exposure has increased substantially, mostly because of the escalating wildfire likelihood and an expanding human-developed footprint.
To address the problem of wildfire events, which are fostered by drought conditions, various strategies have been proposed, including fire suppression and prevention efforts, land management practices, and climate change mitigation measures. Fire suppression and prevention efforts involve reducing the risk of wildfires through measures such as prescribed burning, fuel reduction, and fire breaks (Jazebi et al., 2019; Bertomeu et al., 2022; Lambrechts et al., 2023). Land management practices are generally developed for managing vegetation cover and reducing soil erosion to improve soil moisture retention (Mariani et al., 2022; van Leeuwen and Miller-Sabbioni 2023). Climate change mitigation measures involve reducing greenhouse gas emissions to limit the extent of global warming and its impact on drought conditions (Canosa et al., 2022; Leverkus et al., 2022).
The spatio-temporal variations of the number of events and fatalities in different continents and regions around the world are also of importance when analyzing the relationship between drought and wildfire events. However, there is a lack of comprehensive studies that investigate the long-term trends of both droughts and wildfires. To fill this knowledge gap, the present study focuses on using the Emergency Events Database (EM-DAT, emdat.be) to gather such data and provide valuable insights into this relationship. EM-DAT is a multi-hazard database that has been used as the main source of information by several researchers (e.g., Lesk et al., 2016; Guoqiang & Seong, 2019; Chen et al., 2020; Hamidifar & Nones, 2023) and as validation tool (Winsemius et al., 2013), even if it has some limitations (Petrucci et al., 2019; Saharia et al., 2021).