1. Introduction
Nowadays, wildfires have become one of the most significant disturbances worldwide [
1,
2,
3,
4,
5,
6]. The combination of a longer drought period and a higher woody biomass and flammability of dominant species creates an environment conducive to fire spread [
7,
8]. Furthermore, vegetation pattern changes with the abandonment of traditional rural activities plays a direct role in the increase of fire severity and ecological and economic fire impacts [
1,
9]. Fire behavior exceeds most frequently firefighting capabilities and fire agencies experience difficulties in suppressing flames while providing safety for both firefighters and citizens [
10].
Climate change would have an essential influence on fire regime and ecosystem dynamics [
3]. Therefore, long-term projections were carried out using general circulation models (GCMs) [
11]. However, projections of extreme events, such as droughts and heatwaves, must be analyzed from studies at regional o local scales [
11,
12,
13]. GCMs involve statistical “downscaling” or an empirical relationship between the general circulation variables and local variables, such as convection process and topography [
13,
14]. All CGMs results would fluctuate depending on the assumptions of one or another Special Report on Emission scenarios (SREs) based on the economic and technological development and demographic change (A1, A2 and B1 scenarios) [
15]. These SREs were superseded by Representative Concentration Pathway scenarios (RCPs) [
16]. The four RCPs scenarios, namely RCP2.6, RCP4.5, RCP6 and RCP8.5 were labeled after a possible range of radioactive forcing values in the year 2100 [
16].
The last decade in the northern hemisphere has been the hottest since meteorological records began [
16]. A temperature increase entails a greater risk of large fires because of the lower fuel moisture content (FMC) and the greater fuel availability [
17]. All GCMs show increases in future temperatures, mainly in summer temperatures [
18]. Temperature increases to a greater or lesser degree are based on the selected SREs or RCPs. According to the temperature differences, both scenarios can be used to estimate the decrease on FMC. Therefore, a change in fire intensity and severity [
1,
19], the frequency of large fires [
4,
20] and the annual area burned [
1,
19,
20,
21,
22] can be assumed. This expected fire regime change would lead to higher economic impacts [
6,
23,
24,
25] and to larger fire suppression difficulties [
10,
26], and as a consequence, to higher suppression costs [
27,
28,
29]. The increase of suppression difficulties entails the incorporation of a greater number of firefighting resources in order to mitigate fire-line spread. The suppression difficulties index has a strong relation with the energy release from the fire [
26]. In this sense, we can affirm that the fire virulence and the suppression difficulty conditions will increase under the different climate change scenarios, and as a consequence, also suppression costs.
The aim of this study was to identify economic fire susceptibility of tangible assets and suppression costs under projected climate change (period 2041–2070). A general increase in temperatures and decrease in relative humidity was estimated using a downscaling technique. Given the uncertainty of anthropogenic influences, three future scenarios were proposed based on the modified fuel moisture content and fire behavior over the surface and canopy fuels. Fire behavior was modified unevenly under three future scenarios, increasing the economic impacts and suppression costs of forest fires. Therefore, fire susceptibility under the three future scenarios was estimated integrating tangible assets valuation and potential fire behavior, and as a consequence, net value change of the forest resources [
30]. Finally, we included a comparative analysis of suppression costs in the study area between different periods. Knowledge of future changes in economic susceptibility and suppression costs is needed for constructing adaptation strategies and for developing efficient fire suppression resources allocation for fire prevention and mitigation activities.
4. Discussion
The climate scenarios generated for the first seven decades of the century present robust estimates for temperature [
13,
16]. RCP 2.6 changes are much lower than the rest of the RCPs because it includes the option of using policies to achieve net negative carbon dioxide emissions before the end of the century [
16,
36]. Geostatistical methods using GIS play an important role for extrapolating the climate scenarios to any territory [
33,
34,
35]. Results for our study area shows an increase in the summer temperatures similar to those obtained in other Mediterranean studies [
8,
16,
18,
46]. In recent summers, field inventories in Mediterranean basin have shown values generally smaller than standard values observed for FFMC and LFMC [
47,
48]. According to our results, FFMC and LFMC could decrease between 0% and 2% and between 8% and 18%, respectively. The decrease in FMC has an important effect on fire behavior, and as a consequence, in the large fires’ occurrence [
1,
3,
4,
19,
20,
21,
22]. The integrated use of GIS and fire spread simulators allows us to analyze fire behavior under different FMC scenarios [
39,
40,
41]. Our FMC scenarios showed more severe fire behavior in a similar way than other studies [
1,
19,
20]. Flame length increased from 4.60% to 15.69%, and as a consequence, fire-line intensity increased considerably, ranging from 9.81% to 21.31%. Finally, climate change would raise spread rate between 4.45% and 24.07%. Some studies have shown the effects of climate change in fire intensity and difficulties in suppression flames [
10] and, therefore, in an increase in the economic impacts from wildfires [
6,
9,
24,
25].
The goal of this manuscript has not been to make a dissertation on the consequences of climate change on the socioeconomics of potentially affected Mediterranean ecosystems. However, we consider that the effects of climate change in increasing the intensity and severity of forest fires, imply a greater demand for budgets to increase the contracting of resources from suppression activities. It also implies an increase in the duration of contracts over the months. The effects are of a reduction in the same proportion of the budget allocated to fire prevention and management activities in the fuel treatment. The administrations and departments of prevention and extinction of forest fires have difficulties to obtain increases of budgets to extinction and fire suppression without affecting in reductions in the budgets of prevention. This circumstance is today a reality verified throughout the last 50 years. In addition, and as already demonstrated in the manuscript, the increase in the difficulty of suppression actions is generating a progressive increase in suppression costs.
Unquestionably, the increase in the intensity and severity of forest fires due to climate change [
1,
9,
40] and the high availability of forest fuels (abandonment of the rural environment and decrease in population density) would increase natural resources impacts. In this sense, disturbances and negative effects affect the income of populations when resources such as leisure and recreation are damaged by the strong alteration of the landscape after the fires, in the same way erosion and loss of water quality, are damages in forest landscapes that indirectly imply negative effects on the socioeconomics of the populations affected. On the other hand, one might think that forest restoration work on landscapes affected by fires can be a positive consequence from a socioeconomic point of view, increasing the wages and jobs in the rural economy. This is not entirely true for two reasons: first, the strong budgetary decapitalization of governments and administrations makes it difficult to approve budgets in order to address the financing of restoration work on the large areas affected by large forest fires. Consequently, the generation of job opportunities is not clear. Secondly and from the point of view of investigations of the causes of the forest fires over more than 50 years, important efforts have been made to avoid relating forest fires to the socio-economic benefit of increasing wages for extinction, prevention and the restoration. These control actions are aimed at reducing the arson fires causes. From our point of view, it is difficult to find positive socio-economic effects of climate change on forest fires. Perhaps it could be indicated as a positive effect, the change in the combustibility that occurs in the landscapes affected by large fires, decreasing of high intensity fires in the following decades, so the slow recovery of damaged resources. It will be guaranteed in one way or another, as well as the protection and defense of populations located in forest areas.
The economic susceptibility of the forest resources in the study area is about 918 million Euros according to the baseline period. Fire impacts pointed to the importance role that carbon storage (22.10% of the total loss), timber (21.34%) and firewood (20.67%) resources play in the rural study area. The effect of climate change on individual resources is uneven. For example, while acorn production impact increases considerably (
Table 6), chestnut production impact is slightly affected, due in part to its location in humid areas filled with debris and isolated understory. Some resources, such as cork oak, pasture production and game, have shown few changes under the favorable and intermediate scenarios (S2 and S3 scenarios), but larger changes for the most unfavorable scenario (S1 scenario). As an example, a livestock exclusion is needed in pasture production resource for the highest fire intensity levels [
41,
44]. It can be observed in the differences between baseline period, S2 and S3 scenarios and S1 scenario (an increase of 46% of the economic impacts). In general, climate change would increase the economic susceptibility of the study area between 63,632,966€ or 6.05% (baseline period-S3 scenario) and 255,087,946 or 25.99%€ (baseline period-S1 scenario) (
Table 9).
Climate change has accentuated the virulence and the suppression of difficulties of large fires leading to an increase of suppression costs [
27,
28,
29,
49]. Although there is a wide burned area range according to the standard deviation, an upward trend can be seen in the last decade in relation to burned area (6167 ha compared with 2984 ha) and burned area per unit time (88.56 ha/h compared with 59.60 ha/h) (
Table 6). These burned area trends and the significant statistical difference found in the control time (95.75 h compared with 49.25 h) seem to suggest that there is an increase in suppression difficulties [
26]. Significant statistical differences were found between 1990–2005 large fires and 2005–2015 large fires from total suppression costs and suppression costs per unit time. The comparative analysis confirmed a general increase in cost per unit area (86.73%) and cost per unit time (65.67%), mainly in relation to the increase in aerial resources cost (818,348€ compared to 110,706.01€). This increase in aerial firefighting operations responds both to the number of aircraft and to the number of hours worked between the two time periods considered. According to fire size costs, we found an average rate of 1.41-fold increased suppression costs between the two time periods considered. It is an interesting outcome that suppression costs have increased in recent years in association with a decrease on FMC was induced by an increase in temperature and a decrease in relative humidity.
Suppression costs are based on the real data and official prices for the study area. In this sense, our findings highlight the increase of suppression costs in the last decade. The average suppression cost per fire size [
49] can offer the possibility to study in depth the behavior of the suppression costs over time based on fire size. Measuring techniques would have most likely greatly improved for the time period considered (2041–2070). Although fire suppression techniques have improved from 1990 to 2019, fire suppression costs have increased as reported in this and other studies [
27,
28,
29,
49]. However, increase fire suppression efficiency has not been demonstrated in part due to the generalized decision to send more and more fire suppression resources to fires without knowledge of the resources’ efficiency [
50,
51]. This practice is more evident in high-intensity large wildfires increasing fire suppression costs without a corresponding increase in suppression activities efficiency.
At present, fire suppression costs for the study area in general represent about 65% of the total fire management budget [
52]. The increase in fire intensity leads to higher economic impacts and suppression difficulties [
6,
10,
24,
25], which if not considered leads to higher suppression costs [
1]. Our research only considered suppression costs’ changes. Further studies should include the prevention costs and the relationship between prevention and suppression efforts and costs. Because the important short- and long-term effects and the higher risk of large fires, the national and regional agencies and/or authorities have requested estimations on fire susceptibility and suppression difficulties of wildfires in relation to climate change. Our approach identifies sectors and resources with the highest future economic susceptibility for the considered period (2041–2070). This strategic information plays an essential role in operational priorities and firefighting resources management to increase the efficiency in the provision of fire services and to mitigate the fire impacts. The use of GIS tools increases the flexibility of this approach to include new forest resources and net value changes enabling a further extrapolation to any study area.