Simulating fire regimes in human-dominated ecosystems: Iberian Peninsula case study

“Although there is a general relationship between human population density and fire activity in some regions, these variables are not necessarily linearly related, being strongly influenced by the environmental setting (Venevsky et al., 2002; Syphard et al., 2007; Li et al., 2009).”

“, 2001), the representation of fire regimes (Venevsky et al., 2002), and the simulation of transient vegetation responses to climate warming (Joos et al.”

“Anthropogenic ignition sources are calculated as an increasing function of population density while assuming that people living in sparsely populated regions interact more with natural ecosystems and therefore produce potentially more ignitions (31).”

“SPITFIRE is a process-based global fire model and a further development of the Reg-FIRM approach (Venevsky et al., 2002) but uses a more complete set of physical representations of spread and fire intensity.”

“The Regional Fire Model (Reg-FIRM: Venevsky et al., 2002) introduced a new approach in fire modelling by simulating burnt area as the product of number of fires and average fire size.”

“We investigated the drivers of years with large burned area and the annual trends by decomposing burned area into the number of ignitions and the size of fires (regional burned area D number of ignitions (cid:2) mean fire size) 11 .”

“We approximate T dew (d) by ( T min (d) − 4), where T min (d) is the daily minimum temperature (Running et al., 1987), the same approach used by Venevsky et al. (2002).”

“…of weather, fuel and management-related variables on the spatio-temporal dynamics of wilfire is a " hot topic " that is increasingly examined through landscape fire models (Venevsky et al., 2002; Thonicke and Cramer, 2006; LaCroix et al., 2008; Cary et al., 2009; Parisien and Moritz, 2009).”

“Several studies have focused on developing methods for incorporating fire into DVMs at global (Thonicke et al., 2001; Venevsky et al., 2002) and landscape scales (Keane et al., 1996; He & Mladenoff, 1999; Rupp et al., 2001, 2002).”

“For example, the effect of changes in wind speed on fire spread rates is currently simulated as a simple linear step-up function [ Venevsky et al., 2002 ].”

“For instance, the LPJ, the SDGVM and the SEIB-DGVM (Sato et al., 2007) use fire models that assume that fire frequency is determined by fuel loads and the moisture content of litter and that fires remove a predefined fraction of biomass (Thonicke et al., 2001; Venevsky et al., 2002).”

“Venevsky et al. (2002) and Arora and Boer (in press) have developed fire models of intermediate complexity that allow for variations in ignition rates associated with human activities.”

“…CLM4, CNDV Oleson et al. (2010) LPJ Sitch et al. (2003) LPJ Sitch et al. (2003) LPJ guess Smith et al. (2001) ORCHIDEE Krinner et al. (2005) MC1 DGVM Bachelet et al. (2001) ased on LPJ Venevsky et al. (2002) Earth Observation and Geoinformation 26 (2014) 64–79 67 s G 2 l g i b 1 t r a d a a 2 C –”

“We further extended the CLM-CN-AB version by an explicit treatment of human ignition following Venesky et al.(2002), for which the probability of human ignition increases with population density.”

“…for commercial use or unauthorized distribution. at Geograph Institute Der on June 20, 2007 http://ppg.sagepub.comDownloaded from considered as one of the major drivers for fire regimes (eg, for the Iberian Peninsula – Venevsky et al., 2002; or many Mediterranean countries – Moreno et al., 1998).”

“…of fire into process-based models, but the applications of these models have primarily been focused on retrospective analyses of carbon dynamics (Peng & Apps, 1999; Amiro et al., 2000; Chen et al., 2000, 2003; Thonicke et al., 2001; Venevsky et al., 2002; Hicke et al., 2003; Balshi et al., 2007).”

“This exercise of aggregation of regional analyses to a global picture could complement top-down approaches using global vegetation models (Lenihan et al. 1998; Thonicke et al. 2001 ).”

“The form of nonlinear function has been tested in peninsular Spain by Venevsky et al. (2002) and on a global scale by Pechony and Shindell (2009).”

“First, in all simulations the climate-dependent fire module was used (Thonicke et al., 2001; Venevsky et al., 2002).”

“While several studies have used fire cycle information to account for recurring fires, they generally do not explicitly consider the history of fire across the landscape [e.g., Thonicke et al., 2001; Venevsky et al., 2002].”

“These changes in behavior are the main factors driving the spatial distribution of people in forest areas and of the increase in ignition events (Badia-Perpinyà and Pallares-Barbera 2006; Venevsky et al. 2002).”

“Most global fire models describe fire as a process that is explicitly limited by the number of human or lightning ignitions (Venevsky et al., 2002; Thonicke et al., 2010; Kloster et al., 2012; Li et al., 2012).”

“The procedures used to estimate fire activity differ and are based on topsoil layer moisture content and dead fuel amount[112] on fuel availability and fuel moisture, and presence of an ignition source (anthropogenic or natural by lightning)[113] or on fire danger indices such as the Nesterov fire danger index.[114] F…”

“The RegFIRM fire model (Venevsky et al., 2002), originally developed as an embedded module within the Lund-Potsdam-Jena DGVM (LPJ, Sitch et al., 2003), was one of the first global fire models that contained explicit representations of climatic fire danger and lightning- and human-caused wildfire…”

“When field-collected fire records are unavailable, fire occurrence can be estimated from remote sensing sources such as burned area products or hotspots (Venevsky et al. 2002; Vadrevu et al. 2006; Maingi and Henry 2007; Chuvieco et al. 2008; Garcia-Gonzalo et al. 2012; Marques et al. 2012; Zhang et al. 2013; Li et al.…”

“Human ignition probability was accounted for following a relationship given by Venevsky et al.(2002), which assumes that an average person is more likely to cause a fire in sparsely populated regions, as they interact more with the natural ecosystems, compared to persons living in densely populated…”

“With the advent of fully dynamic vegetation-fire models (Lenihan and Neilson, 1998; Thonicke et al., 2001; Venevsky et al., 2002; Prentice et al., 2007), exploration of the relative importance of different mechanisms in driving changes in fire regimes through comparing carefully-designed…”

“In short, wildfire models (e.g., NWGC 2002, Venevsky et al. 2002, CFS 2007) involve multiple components (i.e., ignition and propagation submodels) comprising numerous parameters that still need to be adapted and calibrated to the biophysical characteristics of the diverse Amazon landscapes.”

“Published fire models (Kloster et al., 2012; Li et al., 2012; Pechony and Shindell, 2009; Venevsky et al., 2002) generally include ignitions from lightning and human sources, together with explicit or implicit human suppression of fires.”

“This approach, based on Venevsky et al. (2002), always leads to an increase in burned area if ignitions increase, all else being equal.”

“Following previously used approximations (Venevsky et al., 2002; Thonicke et al., 2008), we set the dew point temperature which is required to calculate the Nesterov Index to the daily minimum temperature minus 4 K (Running et al.”

“Venevsky et al. [2002] suggested a model that uses the Nesterov fire danger index,whichrelies onthedew-pointdeficit andprecipitation, to estimate the number of fires in a region.”

“Moreover, the combination of drier and warmer climate and more flammable vegetation may result in novel disturbance regimes (Venevsky et al. 2002), leading to autosuccesional dynamics and contingent dynamics (Zavala, Espelta & Retana 2000; Carri on et al. 2001a).”

“However, those models that explicitly include anthropogenic fire generally focus on human impacts on ignitions and furthermore employ either a universal population density value as a threshold for anthropogenic fire ignitions [47], or single-peaked global function of population density [48].”

“, urbanization, described as the ratio of rural to total population (RUR) (higher rural population is a major source of pyrogenic activity with longer contact with flammable vegetation); and (3) combined fire suppression and management, a proxy being the distance to human settlements (cities) (DIS; km), which is also…”

“From this dataset, we calculated the daily Nesterov index NI(d) (Nesterov 1949) which is summed for all days with ≤3 mm precipitation and calculated from daily maximum and minimum temperatures Tmax(d) and Tmin(d) as in Venevsky et al (2002): NI(d) = ∑ Tmax(d) ∗ [Tmax(d)− (Tmin(d)− 4)].”

“The Nesterov Ignition Index is widely used in forest fire research (e.g. Viegas et al. 1999; Venevsky et al. 2002), but it did not perform well in our study region.”

“Anthropogenic ignitions are estimated as a function of population density with the maximum ignition being obtained at ca. 16 indkm−2 (Venevsky et al., 2002; Thonicke et al., 2010).”

“At regional or global scale, fires are determined by climate variability, human activities and vegetation distribution, and in turn they feed back on vegetation distribution and structure, the carbon cycle, and climate (Venevsky et al. 2002; Pausas and Keeley 2009; Bowman et al. 2009).”

“Venevsky et al (2002) introduced the concept that each person, on average, starts a given number of fires per unit time.”

“DTR has been long used as predictor for fire weather conditions because it is sensitive to stable weather conditions that are usually associated to low humidity and are supportive for fire activity (Bistinas et al., 2014; Venevsky et al., 2002).”

“In this ignition mode, anthropogenic ignition and suppression depends on population density (PD), as proposed by Venevsky et al. (2002).”

“In many areas fire is the most important type of natural (and/or human) disturbance affecting biogeochemical cycles and we have many examples of researchers incorporating fire modules in DGVMs (e.g. Thonicke et al. 2001, Venevsky et al. 2002).”

“The oscillations at high FWI may be due to a lack of data, but could also arise from human behaviour: during heatwaves, (hence, extreme FWI), human activity will be reduced and so fewer fires will be started (Venevsky et al. 2002).”

“, 2007) and simulate the occurrence and effects of fire (Venevsky et al., 2002; Scheiter & Higgins, 2009; Thonicke et al., 2010).”

“A fire ignition model has been implemented within PESERA, using simplified versions of algorithms developed and tested independently (Venevsky et al., 2002) for the Iberian Peninsula.”

“…as Ia ¼ PDαk PDð Þ (5) where PD is population density (person km 2); α is the daily potential anthropogenic ignitions (1.3 × 10 4, count person 1 d 1); and k(PD) is a population density-related parameter for adjusting anthropogenic ignition potential (=6.8PD 0.6) [Venevsky et al., 2002].”

“Such linkages make the simulations of AABmore complicated if both FS and number of fire occurrences are modeled jointly (e.g. Venevsky et al 2002, Westerling et al 2011, Veraverbeke et al 2017).”

“The index derived as an empirical function reflecting the relationship between fire and weather based on historical data (Venevsky et al., 2002).”

“…litter drying rate is described by the cumulative Nesterov fire danger index (NI; Nesterov, 1949) as described by Running (1987), and a fuel-specific drying rate parameter ( α xhr ; Venevsky et al., 2002) which was tuned to provide the best results against fire observations (Thonicke et al., 2010).”

“Among the most used indices in these systems or in experimental studies, we can cite McArthur index (FFDI) [23], Canadian Fire Weather Index (FWI) [19], Swedish Angstrom index (I) [24], Keetch–Bryam Drought Index (KBDI) [20], Russian Nesterov Index (NI) [25], Russian Modified NI (MNI) [26], Zhdanko index (Zh) [27], Au…”

“SPITFIRE quantifies human-caused fire ignitions based on a simple approximation of ignition scaling with human population density [Venevsky et al., 2002], an approach that is now widely used in other global fire models [e.g., Arora and Boer, 2005; Kloster et al., 2010] and confirmed to be…”

“Models of transient vegetation and fire dynamics (Lenihan et al. 1998; Thonicke et al. 2001) are currently being applied (Bachelet et al. 2000; Venevsky et al. 2002; Bachelet et al. 2005) to evaluate regional responses of fire regime to projections of future climate change.”

“In RETRO, the Regional fire model (Reg-FIRM) is used to provide estimates of the burned area variability based on the climate data (Venevsky et al., 2002).”

“Like most fire models, ignitions are also based on global-scale relationships of population density (Hantson et al., 2016), developed by early fire modelling studies (e.g., Mangeon et al., 2016; Venevsky et al., 2002).”

“Anthropogenic effects on fire most commonly are modeled as dependent solely on population density, not land use (e.g., Venevsky et al., 2002; Arora and Boer, 2005; Pechony and Shindell, 2009; Thonicke et al., 2010; Li et al., 2012; Melton and Arora, 2016; Hantson et al., 2016; Rabin et al., 2016).”

“Human influence is usually included as a function of population density (Venevsky et al., 2002; Pechony and Shindell, 2009), although some authors have noted that such relationships are too simplistic, with the effect of population density actually varying based on biome or amount and type of land…”

“…(4) Where β is defined as: β ¼ max 0;min 1; LF LFlow LFup LFlow (5) [23] The human ignition probability (IP_Ph) is described by using the relationship developed by [Venevsky et al., 2002], further modified by Kloster et al., [2010], which relates fire occurrence to population density (ρ) in terms…”

“Venevsky et al. (2002) showed a logarithmic increase in fire frequency with human population density.”

“Venevsky et al. (2002) used an exponential function to relate the number of ignitions by humans to population density.”

“The fire count in BASE-Fire is modeled as the sum of anthropogenic ignition and natural ignition, where the latter is proportional to lightning density (Prentice and Mackerras, 1977) and the former is determined by population density (Venevsky et al., 2002).”

“, population density) that are constant across vegetation types (Venevsky et al., 2002; Hantson et al., 2016; Rabin et al., 2017).”

“Many studies conducted at local [e.g., Guyette et al., 2002; Martell et al., 1989], regional [e.g., Venevsky et al., 2002; Costa et al., 2011], and global [e.g., Pechony and Shindell, 2009] scales apply an empirical relationship between population density and anthropogenic ignition sources and…”

“Population density (PD) has been considered a good estimator of ignition sources in populated territories, such as peninsular Spain, in previous fire regime modeling efforts (Venevsky et al. 2002).”

“vegetation distribution are the more sensitive drivers of fire [10,11].”

“In addition to allowing for the characteristics of potential fire danger, account must be taken of the influence of local anthropogenic [19] and natural (lightning activity) impacts on the likelihood of fire emergence.”

“SPITFIRE is a process-based global fire model and a further development of the Reg-FIRM approach (Venevsky et al., 2002), but uses a more complete set of physical representations of spread and fire intensity.”