Temperature determining larger wildland fires in NE Spain

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TAAC-D-14-00118R2 Temperature determining larger wildland fires in NE Spain JOURNAL: Theoretical and Applied Climatology

Temperature determining larger wildland fires in NE Spain D.M.Molina-Terrén 1,*Phone+34 973 70 [email protected] A.Cardil 1 1School of Agrifood and Forestry Science and EngineeringUniversity of LleidaAv. Rovira Roure 19125198LleidaSpain Abstract Significant relationships were found between high-temperature days and wildland fire occurrence in the 1978–2011 period in Aragón (NE Spain). Temperature was analyzed at 850 hPa to characterize the low troposphere state, avoiding problems that affect surface reanalysis and providing regional coverage. A high-temperature day was established when air temperature was higher than 20 °C at 850 hPa. The number of these days increased significantly in the study period, increasing the frequency of adverse weather conditions that could facilitate extreme fire behavior. Specifically, these high-temperature days are more frequent in June than they used to be. The effects of those high-temperature days in wildland fire patterns were significant in terms of burned area, number of wildland fires, and average size. Fires larger than 60 ha were the subject of this study. These wildland fires have been increasing in number and size in the last years of the series. Abstract AQ2 ᅟ

1. Introduction Heat waves are usually renowned to damage agriculture, forests, and economic activities and also can play a key role also in terms of human health issues (Kuglitsch et al. 2010; Trigo et al. 2006; Mills 2005). Southern European countries like Spain have many wildland fires each year (Salis et al. 2012; Pereira et al. 2011). Fire has always been part of the traditional Mediterranean agrarian land management, occasionally evolving into unwelcome wildfires (Molina et al. 2010; Millán et al. 1998). Nevertheless, over the past 40 years, wildland fires have turned

into more dangerous, with fire behavior often exceeding firefighting capabilities (Miralles et al.2010; Molina et al. 2010) and wildland fire agencies are having difficulties in suppressing extreme-behavior fires while providing safety for both firefighters and citizens, as reviewed in Werth et al. (2011). The social environment has changed dramatically, and wildfires regularly obtain significant attention from the media in summer in Spain. Agricultural abandonment is a major cause of an increased fuel load (Millán et al. 1998), and wildland fuel homogeneity and continuity are also major facilitators of fast fire propagation (Molina et al. 2010; Vega-García and Chuvieco 2006). Moreover, climate and weather are two of the key factors influencing fire regimes (Trouet et al. 2009) and climate change could have a significant impact on ecosystems due to increases in area burned and fire intensity/severity (Flannigan et al. 2000). Regato (2008) and Giannakopoulos et al. (2009) showed that climate change could provide an increase in the intensity and frequency of summer heat waves (short periods with very hot days, with very low air humidity, and frequently with strong winds) that increase the probability of main wildland fire (MWF). Main wildland fires in the Mediterranean Basin are defined in this work as those over 60 ha that accounted approximately for 85 % of the total area burned in NE Spain in the 1978–2011 period (i.e., Aragón). Typically, few MWFs cause the majority of the damage to the vegetation structure (Ganteaume and Jappiot 2012; Alvarado et al. 1998) because they account for a very high percentage of the total burned area (Stocks et al. 2003) and their severity is normally higher (Molina et al. 2010). Additionally, in these MWF events, suppression is often compromised and involved firefighter safety issues. Therefore, MWFs have a significant effect in ecosystems and human safety and properties (Alvarado et al. 1998) and also request massive means to suppress them. It is crucial to discern which factors influence MWF. Several works (Trigo et al. 2006; Mills 2005) have studied high-temperature days (HTDs) and their potential impact on the development of MWF from a point ignition. Preceding studies show that HTD might provide more extreme weather conditions (Montserrat 1998), which have an important role in forest fire behavior (Crimmins 2006) as well as they allow fires to grow larger. A high-temperature day causes a decrease in fuel moisture content and makes more likely extreme fire behavior by convection and mass transfer processes (i.e., crown fires and spotting or long-distance ignition by convection processes). Therefore, a HTD has the potential to increase the probability of having MWF. In a similar way, Mills (2005) indicates that unusually strong temperature gradients at 850 hPa may have the potential to identify remarkably severe fire weather events. It would be extremely profitable to be able to discriminate between the simply “bad” and the “disastrous” fire days with some reasonable lead time (i.e., 24 or 48 h). The five largest MWFs on record in Aragón did develop under HTD. The largest fire in Aragón affected 16,832 ha in Villarluengo (Teruel) in 2 July 1994, and air

temperature at 850 hPa and at 00:00 UTC in the Aragón region was higher than 22.5 °C, during the day of the fire and also in the two previous days. In this circumstance, the synoptic weather pattern that triggered the HTD was a hot air mass inlet (south advection from the Sahara desert). The examination for original causes and observable patterns of MWF is instrumental to both predict extreme fire behavior and plan the best suppression strategies. In this study, we have investigated HTD in Aragón (NE Spain) and their liaison to the MWF official records both in terms of amount and cumulative area burned, and number and average size. Also, for those days having at least one MWF from June to September, we have compared the following parameters of wildfire activity in HTD and non-HTD: (i) average daily number of MWF, (ii) average daily area burned per MWF, and (iii) percentage of days with MWF. 2. Methods 2.1. Study area

Aragón is located in NE Spain. The region has 1.34 million inhabitants and comprises the provinces of Huesca, Teruel, and Zaragoza, and it is politically divided in 33 counties. It is the fourth largest region in Spain (47,719 km2). Aragón has diverse ecosystems because there is a high altitudinal gradient. There is a major river (Ebro) bordered by two mountain chains, the Pyrenees (maximum altitude 3404 m, Aneto) and the Iberian System (maximum altitude 2314 m, Moncayo). Aragón climate, it is generally regarded as a Mediterranean with continental tendencies but the complex topography influences it and generates diverse local climates. The environment varies from the high mountains of the north-central Pyrenees, with perpetual ice (glaciers) to semi-desert areas such as Monegros’ steppe. The mean annual temperature ranges from 5 °C in the highest areas of Pyrenees to 22.5 °C in the Ebro valley, and the average annual rainfalls also ranges from 300 mm in the valley to 1800 mm in the highest mountains (AEMET 2011). Wildland vegetation types are the result of topography and climate. In the Ebro valley, oaks and junipers are the most frequent trees and there are degraded areas covered by grasslands and shrubs. In upland areas, there are several tree species (pine, fir, beech, oak), meadows, and shrubs. AQ3 2.2. High-temperature days in Aragón

Reanalysis data from the National Centers for Environmental Prediction (NCEP) were used to characterize the high-temperature days (Kalnay et al. 1996) as in other works (Bedia et al. 2012). We examined daily air temperature maps (850 hPa at 00Z) to assess whether there was a HTD condition in the study area. We decided

that there was a HTD when air temperature at 850 hPa was equal or higher than 20 °C in at least two thirds of the Aragón region because it is approximately in the 90th percentile in the summer season (June–September). We selected the temperature at 850 hPa because it is commonly used to examine past fire weather and to forecast fire weather (García-Ortega et al. 2011; Trigo et al. 2006; Millán et al. 1998). At this air pressure (850 hPa), we obtained a regional reportage of the temperature and it is adequately close to the Earth surface to characterize the low troposphere state. Additionally, at this air pressure, we avoided some of the problems that affect near-surface reanalysis variables (Trigo et al. 2005; Ogi et al. 2005). An air temperature at 850 hPa equal or higher than 20 °C is commonly correlated with heat waves, and this state provides both high air temperatures and low relative humidity in the Earth surface (Montserrat 1998). Every day from 1978 to 2011 from June to September (included, i.e., summer season), weather conditions were characterized. We studied HTD number, frequency, and periods as a proxy for potential fire behavior. We defined “HT periods” as the number of continuous times that a HTD happened. 2.3. Main wildland fires

In this work, main wildland fires (MWFs) are defined as those over 60 ha. MWFs were 2.5 % of the total number of fires and accounted approximately for 85 % of the total area burned. We have examined trends in the number of MWFs, MWF area burned, and average MWF size under both HTD and non-HTD. We used the historical fire data (1978–2011 period) from Wildland Fire National Statistics (EGIF) of the Agency for Protection against Forest Fires (ADCIF) of the Ministry (MMAMRM) of Environment and Rural and Marine Affairs. This comprises the Wildland Fire Reports sent to the MMAMRM by the Fire-Fighting and Forest Management Services of all the Spanish regions. This Spanish National Administration is in charge for compiling statistics, backup regional firefighting actions, and coordinating fire suppression at the national level. Nevertheless, fire prevention and suppression activities are carried out autonomously by regions (i.e., Aragón in NE Spain). This database has a record from each fire, regardless of size, and contains the same fields of information for each fire. We did not use the first years of this database (1968–1977), because areas burned in private properties were usually underreported in those years (Cardil and Molina 2013). Most fire sizes recorded were obtained from fire perimeters acquired from GPS follow-up either by helicopter or by terrestrial ground checks. In this period, there were 216 wildland fires in Aragón (NE Spain) larger than 60 ha that burned approximately 130,000 ha approximately from June to September. Each of them might have affected forest and agricultural areas, roads, and people. Wildland fires are mostly happening from June to September. Therefore, this work focused on the June–September season. In many Mediterranean ecosystems, a

restricted number of large wildland fires accounts for a large amount of the total burned area (Salis et al. 2012; Molina et al. 2010). We examined MWF considering different size classes in relation to the percentage of burned area with respect to total burned area (Table 1): MWF60 (i.e., fires larger than 60 ha), MWF100, MWF250, and MWF500.

Table 1

Historical relationship between fire MWF classes and percentage of fire number and burned areas in Aragón, from

MWF classes Percentage of the total burned area (%) Percentage of t

MWF60 84.7 2.5

MWF100 80.8 1.8

MWF250 71.4 0.9

MWF500 61.3 0.5

MWF60 (fires larger than 60 ha), MWF100 (fires larger than 100 ha), MWF250 (fires larger than 250 ha), MWF500 (fires l

2.4. Statistical analysis

The relationship between HTD and MWF was assessed in the period up to 2 days immediately before MWF occurrence date and analyzed according to the following four HTD categories over the study period: Category A: MWFs that start on a HTD (day 0), HTD (day 1), and HTD (day 2). Therefore, MWF under a very strong HT period. Category B: MWFs that start on a HTD (day 0), HTD (day 1), and non-HTD (day 2). Therefore, MWF under a strong HT period. Category C: MWFs that start on a HTD (day 0), non-HTD (day 1), and HTD or non-HTD (day 2). Therefore, MWF under a weak HT period. Category D: MWFs that start on a non-HTD (day 0), HTD or non-HTD (day 1), and HTD or non-HTD (day 2). Therefore, these were wildland fires in which HTD conditions were negligible. Only 2 days before all MWFs have been used in this analysis. Several days before each MWF were analyzed (5 days) but they did not influence the results, and additional previous days (day 3, day 4, and day 5) did not supply more information than HT categories used (above). We evaluated the influence of HTD on MWF in three consecutive days by using an ANOVA analysis and group comparison by the

Fisher method with a 95 % confidence interval. The meeting of ANOVA assumptions was confirmed. We also quantified how many MWFs were conditioned by HTD (only in the day that the fires started), and we summarized statistics in the studied period. We established the number of MWFs, burned area swept by them, and the average size and percentage of MWF under HTD and non-HTD. We determined if there were significant changes (decrease, increase, no difference) in the studied variables (number of MWFs, area burned by MWF, and number of HTD) from 1978 to 2011 with a linear regression analysis on annual raw data. To study the relationship between HTD and main wildland fires (MWFs), we defined the next indicators: (1) number of HTD with at least one MWF, as a percentage of the total HTD; (2) normalized MWF average number per HTD with MWF; (3) normalized MWF average area burned per HTD with MWF; and (4) area burned by MWF under HTD, as a percentage of the total area burned by MWF. In this context, “normalized” is to represent an equivalent 10,000 ha area. To assess significant differences among HTD and non-HTD, we perform the same calculations on non-HTD. HTDs were mostly in the June–September time frame; therefore, we compare the HTD versus non-HTD in those months (i.e., summer season thereafter). 3. Results 3.1. HTD trends

In Aragón, the annual number of HTD increased significantly (p value = 0.035) in the study period (1978–2011). It rose from 8 HTDs in 1981 to 15 in 2008 in terms of 7 year average values. The number of HT periods also increased (p value = 0.025). Therefore, in latest years, we have more HTD periods. However, HT periods had the average length of 2.2 days and did not change along the study period. Most HTD events happened in mid-summer (July and August) accounting for more than 80 % of the total HTD. June has 11.5 % of HTD and September 5.8 % of HTD. June rose significantly the number of HTD from 0.7 days in 1981 to 2.7 in 2008 in terms of 7 year average. In July, August, and September, no significant trends were observed. 3.2. Large wildland fires

In Aragón, there was a decrease in the total annual number of MWFs (p value = 0.004). It declined from 12 MWFs in 1981 to 3 MWFs in 2008 (reported as 7-year average values). The annual number of MWF under non-HTD also decreased significantly (p value < 0.001). It contracted from 8 MWFs in 1981 to 1

MWF in 2008 in expressions of 7-year average values. By contrast, the annual number of MWFs under HTD did not decline. Neither total annual area burned nor annual area burned under HTD changed in the study period. However, a significant shrinkage was found in the annual area burned under non-HTD (Table 2). It diminished from 1854 ha in 1981 to 641 ha in 2008 in 7-year average values.

Table 2

Trends in annual number of main wildland fires (MWFs), annual area burned, and annual number of high-tempe June to September (1978–2011)

Variable Total HTD

Number of MWFs − (<0.004) ns (0.293)

Area burned ns (0.896) ns (0.684)

HTD + (<0.035)

Values in parenthesis are the p statistic

+ significantly increased, − significantly decreased at p < 0.05, ns not significant

HTD also influenced the average MWF size (Table 3) in all MWF classes (MWF60, MWF100, MWF250, MWF500). Figure 1 shows all fires (under HTD and non-HTD) larger than 60 ha in Aragón from 1978 to 2011. Additionally, when using the influence of previous days, HTD categories explain also the variable average magnitude of the MWF (p = 0.006). Table 4 lists the number of MWF, area burned, and average dimension of MWF in each HTD category. The HTD category examination exhibited that there was a significant difference between both A and B categories and D category. Average MWF size in D category was a third that of those in both A and B categories (Table 4). There is not a significant difference among C category and other categories. Additionally, the influence of HTD in the largest fires in Aragón is clear. The 74.2 % of the area burned in fires larger than 500 ha were under HT conditions. This value increased to 81.5 % in the area burned in fires larger than 1000 ha. This is a clear contrast to the 22.3 % in the total area burned under HTD in fires between 60 and 100 ha (Table 5).

Table 3

Comparison between high-temperature days (HTDs) and non-high-temperature days (non-HTDs), in those days fire (MWF) from June to September (1978–2011) in terms of (i) average daily number of MWF, (ii) average da average MWF size

MWF class MWF average daily number per HTD/non-HTD with MWF

MWF average daily area burned per HTDHTD with MWF

MWF60 Significant difference (0.001) Significant difference (<0.001)

MWF100 Significant difference (0.014) Significant difference (0.002)

MWF250 Significant difference (0.033) Significant difference (0.006)

MWF500 No significant difference (0.446) Significant difference (0.032)

Values in parenthesis are the p statistic. MWF60 (fires larger than 60 ha), MWF100 (fires larger than 100 ha), MWF250 ( MWF500 (fires larger than 500 ha)

Fig. 1 Fires larger than 60 ha (LWF60), 100 ha (LWF100), 250 ha (LWF250), 500 ha (LWF500), and 1000 ha (LWF1000) under high temperature condition (HTD) and non-high temperature days (non-HTDs) in Aragón from 1978 to 2011

Table 4

Number of main wildland fires (MWF), area burned, and average size in high-temperature (HT) categories from J

Categories Numberof fires

Averagesize (ha)

Areaburned (ha)

Annual number of fires

1978–1994

Annual number of fires

1995–2011

An burn

A 30 1195 35,837 1.12 0.65 1499

B 30 1157 34,716 1.12 0.65 1015

C 25 612 15,310 1.18 0.29 696

D 131 340 44,492 6.24 1.47 1919

Total 216 603 130,354 9.65 3.06 5130

A: MWFs that start on a HTD (day 0), HTD (day 1), and HTD (day 2). B: MWFs that start on a HTD (day 0), HTD MWFs that start on a HTD (day 0), non-HTD (day 1), and HTD or non-HTD (day 2). D: MWFs that start on a non-H (day 1), and HTD or non-HTD (day 2)

Table 5

Percentage of fires and burned area under high-temperature days (HTDs) in several fire size categories from June

Fire size class (ha) Percentage of fires under HTD of the total fire number in the corresponding fire size class

Percentage of burned area under H corresponding

60–100 22.0 22.3

100–250 38.2 37.2

250–500 43.3 44.0

>500 54.7 74.2

>1000 72.0 81.5

The study period was split in two equal length intervals (1978–1994 and 1995–2011). In the first half period, most MWFs were under D category with 9.65 MWFs and 1919 ha burned per year. In the second half period, outcomes were different, the annual number of MWFs was 1.47, and the area burned per year was 698 ha (Table 4). On the other hand, in HTD categories (A, B, and C), neither annual number of MWF nor annual area burned decreased significantly among the two time halves. The percentage of MWF number under HTD versus total MWF number

was 51.9 %, and the MWF area burned under HTD versus total MWF area burned was 72.5 % in 1995–2011 period. From 1978 to 2011, the ratio of MWF number under HTD versus total number of MWFs rose from 0.30 in 1981 to 0.65 in 2008. In a similar way, the ratio of MWF area burned under HTD versus total area burned also increased from 0.49 in 1981 to 0.85 in 2007. These ratios are in 7-year moving average. The HTD influence in MWF augmented during the study period with two ratios that indicate that most MWFs happen under HTD in recent years. Note that that was not the case in the 1980s and 1990s. In Aragón, there were significant differences among HTD and non-HTD in terms of both MWF daily area burned and MWF daily number in all MWF categories excluding MWF500 category in terms of LWF daily number (Table 3). The average daily area burned per HTD with MWF in MWF60 category was significantly higher (1393 ha day −1) than that in non-HTD (541 ha day −1) (Table 6). The same was detected with the average daily number of MWF in HTD and non-HTD (1.4 ha day−1 vs. 1.1 ha day−1 respectively) (Table 6). In the other MWF categories, similar results were obtained (Tables 3 and 4). Furthermore, the probability of having a MWF is higher under HTD than in other non-HTDs. While the percentage of HTD with MWF60 was 15.0 %, this percentage under non-HTD was 3.1. Equivalent facts were observed in the other MWF categories, with higher differences among HTD and non-HTD in larger MWF categories (Table 3).

Table 6

Relationships between main wildland fire (MWF) classes and days classified as high-temperature days or non- HTDs) in Aragón from June to September (1978–2011)

MWF60 MWF100

HTD AQ4

Number of days classified as HTD 407

HTD with MWF (%) 15.0 12.8

MWF average number per HTD with MWF 1.4 ± 0.12 1.4 ± 0.12

MWF average daily area burned per HTD with MWF (ha, day 1) 1393 ± 361 1604 ± 416

Average MWF size (ha) 1010 ± 250 1149 ± 268

Table 6

Relationships between main wildland fire (MWF) classes and days classified as high-temperature days or non- HTDs) in Aragón from June to September (1978–2011)

MWF60 MWF100

MWF area burned during HTD/MWF total area burned (%) 63.3 64.9

Non-HTD

Number of days classified as non-HTD 3741

Non-HTD with MWF (%) 3.1 2.1

MWF average number per non-HTD with MWF 1.1 ± 0.03 1.1 ± 0.04

MWF average daily area burned per non-HTD with MWF (ha, day 1) 541 ± 91 507 ± 75

Average MWF size (ha) 383 ± 57 451 ± 56

MWF area burned during non-HTD/MWF total area burned (%) 36.7 35.1

Regarding area burned by MWF, the worst years were 1994 and 2009 with 32,600 and 21,925 ha, respectively. In these 2 years, more than 90 % of the total burned area was burned under HTD conditions. These years also have a very high annual number of HTD, 27 HTDs in 1994 and 23 in 2009. The average number of HTDs is 12 per year in study period. 4. Discussion Key components for adverse fire weather projections are high temperatures, low humidity, and strong winds near the ground surface. Weather-related indexes planned to assess spatial and temporal variations in those main elements are not frequently used or available by all fire meteorological prediction agencies (Charney and Keyser 2010; Crimmins 2006). For that very reason, we highlight the importance of discerning between HTD and non-HTD defined by 850 hPa synoptic conditions in planning pre-suppression efforts to anticipated large fires. The number of HTDs increased along the years, and this agrees with Rodriguez-Puebla et al. (2010). This intensification might be related mainly to the weather regime that transports warm, desiccated air masses from North of Africa

(Rodriguez-Puebla et al. 2010). This rise in HTD could be associated to an increase of air temperature in NE Spain because of recent climate change (Moreno 2005; Giannakopoulos et al. 2009, and Kettunen et al. 2007). Giannakopoulos et al. (2009) advised that the number of hot days (Tmax > 30 °C) and heat wave days (Tmax > 35 °C) will rise in Spain. Giannakopoulos et al. (2009) projected that, in Spain, we will face one to three added hot weeks per year. Mega-heat waves are forecasted to increase by a factor of 5 to 10 within the next 40 years (Barriopedro et al. 2010). It has been predicted that mean annual temperature will rise and the greatest warming up rate is advised for Southern Europe (Moreno 2005; Kettunen et al. 2007). In the same direction, fire weather index will rise in summer; (i.e., increasing fire risk) as stated by Van Wagner and Pickett (1985). As a result, HTD will become more numerous, and adverse fire behavior will be enhanced. These HTD conditions are able to decrease wildland fuel moisture and, therefore, to provide for a hostile wildland fire scenario. Our data showed that whereas fires from 60 to 100 ha, under HTD, were 22.3 % of the total burned area in this size class, fires larger than 500 ha under HTD account for the 74.2 % of the total burned area. Moreover, this value rose to 81.5 % in fires larger than 1000 ha. In the future, as our data illustrates, we might be expecting larger fires and could face extreme-behavior wildland fires beyond our firefighting capacity. This is in agreement with what other papers have suggested (Molina et al. 2010; Miralles et al. 2010). It is also in agreement with Bedia et al. (2012) when they state that NCEP data is useful for the identification of extreme fire danger events. (e.g., those above the 90th percentile value) and for the definition of danger levels/classes. AQ5 Another major fact related to HTD is that the increase of the fire season length might be happening already. The number of HTD in June increased in the last years of series, and therefore, in the next years, the fire season could start earlier. Both the total annual number of MWFs and the annual number of MWFs under non-HTD decreased in Aragón from 1978 to 2011. Nevertheless, the annual number of MWFs under HTD did not decrease in the same period. The total annual area burned did not decrease due to the area burned by MWF under HTD. However, a decrease in the annual area burned under non-HTD conditions was observed. Similar results were obtained in other studies in Europe (Cardil et al. 2014). Additionally, the percentage of both MWF occurrence and area swept by MWF under HTD also increased. Three main reasons could explain this. First, the number of HTDs was greater at the end of the time series and it is more likely to have a MWF under HTD (15 % of HTD had a MWF vs. 3 % under non-HTD) and both the daily area burned and the daily number of MWFs was higher under HTD than non-HTD. Second, in the last years, fire suppression resources have improved in technology and training and, therefore, MWF under non-HTD can be suppressed more efficiently because the fuel moisture content is higher (than in HTD) and fires

under HTD can propagate faster and stronger. Third, HTD might be more prone to have simultaneous fire events (MWF or smaller fires) that split suppression resources. The average MWF size in all fires increased in the study period (from 532 ha in 1978–1994 period to 830 ha in 1995–2011 period), and this could be related to the major percentage of LWF under HTD in the last years of the series. The average LWF size in both A and B categories was larger than LWF in non-HT conditions or weak HT conditions (categories C and D). The fact that average LWF size increased when resources were better organized and trained than ever reinforces the importance of these HT conditions and their influence on both total and average size per LWF. The largest historical fires in Aragón happened under years with a larger number of HTDs than the average year, i.e., 1994 and 2009. Note that 1994 falls in the first half and 2009 in the second half of our study. The year with highest number of HTDs was 2003 but in Aragón, the burned area was not very high. It is important to note than 2003 had more precipitation than the average year in this period. Specifically, in May, there was 50.63 % more precipitation than average (mean of 27 weather stations in Aragón, AEMET 2011). However, in this year, there were several large wildland fires as in Portugal with extreme fire behavior (Trigo et al. 2006). This supports the statement that HTDs provide more extreme conditions for fire propagation and more difficulties to suppress those fires. This also occurred in other countries (Trigo et al. 2006; Mills 2005) as Russia (2010), Portugal (2003), Australia (different years), Greece (2007), and the USA (2011, 2012). 5. Conclusions There are significant effects of HTD conditions in the number of MWFs, total MWF area burned, and average MWF size in Aragón. If eventually the number of HTDs increases, fire suppression would be compromised. This is likely to happen because our work already shows that the incidence of both the number of HTDs and HT periods has increased significantly. Fire season is starting earlier than in former years because we found more HTDs in June in the second half of this study (an increase in the fire season length). Not all days are equally adverse for wildland fire suppression. There is a need to differentiate among the bad and the “terrible” fire days with some realistic lead time (i.e., 48 h). Following the results of this study, we propose that discrimination be built on forecast of HTD and non-HTD conditions at 850 hPa. In terms of burned area, a decrease was observed only in annual area burned under non-HTD in the studied period. Total area burned is stable in the same period. This may indicate greater fire damage as more area is burned under HTD. Additionally, the daily burned area and percentage of days with MWF under HTD was

significantly higher than in non-HTD. Therefore, days under HT conditions are more likely to produce large fires and, possibly, with an extreme fire behavior. Acknowledgments We are thankful to the Spanish Ministry of Economy and Competitiveness grant named ForBurn Ref: AGL2012-40098-CO3-01. We are also grateful to Pau Costa Foundation and University of Lleida for partially supporting this study. We thank David Merenciano help in several tasks related with this work. References AQ7 AEMET (2011) Iberian climate atlas. Air temperature and precipitation (1971–2000). State meteorological Agency of Spain and Department of Meteorology and Climatology of the Institute of Meteorology, Portugal

Alvarado E, Sandberg DV, Pickford SG (1998) Modeling large forest fires as extreme events. Northwest Sci 72:66–75

Barriopedro D, Fischer EM, Luterbacher J, Trigo RM, García-Herrera R (20101) The hot summer of 2010: redrawing the temperature record map of Europe. Science 332:220–224

Bedia J, Herrera S, Gutiérrez JM, Zavala G, Urbieta IR, Moreno JM (2012) Sensitivity of fire weather index to different reanalysis products in the Iberian Peninsula. Nat Hazards Earth Syst Sci 12:699–708

Cardil A, Molina DM (2013) Large wildland fires in three diverse regions in Spain from 1978 to 2010. For Syst 22(3):526–534

Cardil A, Salis M, Spano D, Delogu G, Molina DM (2014) Large wildland fires and extreme temperatures in Sardinia (Italy). iForest 7:162–169

Charney JJ, Keyser D (2010) Mesoscale model simulation of the meteorological conditions during the 2 June 2002 Double Trouble State Park wildfire. Int J Wildland Fire 19:427–448

Crimmins MA (2006) Synoptic climatology of extreme fire–weather conditions across the southwest United States. Int J Climatol 26:1001–1016

Flannigan MD, Stocks BJ, Wotton BM (2000) Climate change and forest fires. Sci Total Environ 262:221–229

Ganteaume A, Jappiot M (2012) What causes large fires in Southern France. For Ecol Manag. doi: 10.1016/j.foreco.2012.06.055

García-Ortega E, Trobajo MT, López L, Sánchez JL (2011) Synoptic patterns associated with wildfires caused by lightning in Castile and Leon, Spain. Nat Hazards Earth Syst Sci 11:851–863

Giannakopoulos C, Le Sager P, Bindi M, Moriondo M, Kostopoulou E, Goodess CM (2009) Climatic changes and associated impacts in the Mediterranean resulting from a 2 °C global warming. Glob Planet Chang 68:209–224

Kalnay E et al. (1996) The NCEP/NCAR 40-year reanalysis project. Bull Am Meteorol Soc 77:437–471

Kettunen M. Terry A, Tucker G, Jones A (2007) Guidance on the maintenance of landscape features of major importance for wild flora and fauna—Guidance on the implementation of Article 3 of the Birds Directive (79/409/EEC) and Article 10 of the Habitats Directive (92/43/EEC). Institute for European Environmental Policy

Kuglitsch FG, Toreti A, Xoplaki E, Della-Marta PM, Zerefos CS, Türkeş M, Luterbacher J (2010) Heat wave changes in the eastern Mediterranean since 1960. Geophys Res Lett 37:L04802. doi: 10.1029/2009GL041841

Millán MM, Estrela MJ, Badenas C (1998) Meteorological processes relevant to forest fire dynamics on the Spanish Mediterranean coast. J Appl Meteorol 37:83–100

Mills GA (2005) A re-examination of the synoptic and mesoscale meteorology of ash Wednesday 1983. Aust Meteorol Mag 54:35–55

Miralles M, Kraus D, Molina DM, Loureiro C, Delogu G, Ribet N, Vilalta O (2010) Improving suppression fire capacity. Research report—European Forest Institute (EFI), pp 203–215

Molina DM, Castellnou M, Garcia-Marco D, Salgueiro A (2010) Improving fire management success through fire behaviour specialists. Research report—European Forest Institute (EFI), pp 105–119

Montserrat D (1998) Situaciones sinópticas relacionadas con el inicio de grandes incendios forestales en Cataluña. NIMBUS 1-2:93–112

Moreno JM (2005) Impactos sobre los riesgos naturales. Riesgo de incendios forestales. Evaluación preliminar de los impactos en España por Efecto del Cambio climático. Spanish Ministry of the Environment, pp. 581–615

Pereira MG, Malamud BD, Trigo RM, Alves PJ (2011) The history and characteristics of the 1980–2005 Portuguese rural fire database. Nat Hazards Earth Syst Sci 11:3343-3358

Regato P (2008) Adapting to global change: Mediterranean forests. IUCN Centre for Mediterranean Cooperation, Malaga, Spain

Rodriguez-Puebla C, Encinas AH, García-Casado LA, Nieto S (2010) Trends in warm days and cold nights over the Iberian peninsula: relationships to large-scale variables. Clim Chang 100:667–684

Salis M, Ager AA, Arca B, Finney MA, Bacciu V, Duce P, Spano D (2012) Assessing exposure of human and ecological values to wildfire in Sardinia, Italy. Int J Wildland Fire. doi: 10.1071/WF11060

Stocks BJ et al (2003) Large forest fires in Canada, 1959–1997. J. Geophys. Res. D Atmos 108:1-12

Ogi M, Yamazaki K, Tachibana Y (2005) The summer northern annular mode and abnormal summer weather in 2003. Geophys Res Lett 32:L04706, doi: 10.1029/2004GL021528

Trigo RM, García-Herrera R, Díaz J, Trigo IF, Valente MA (2005) How exceptional was the early August 2003 heatwave in France?. Geophys Res Lett 32:L10701. doi: 10.1029/2005GL022410

Trigo RM, Pereira JM, Mota B, Calado T, Dacamara C, Santo F (2006) Atmospheric conditions associated with the exceptional fire season of 2003 in Portugal. Int J Climatol 26:1741–1757

Trouet V, Taylor AH, Carleton AM, Skinner CN (2009) Interannual variations in fire weather, fire extent, and synoptic-scale circulation patterns in northern California and Oregon. Theor Appl Climatol 95:349–360

Van Wagner CE, Pickett TL (1985) Equations and FORTRAN program for the Canadian Forest Fire Weather Index System. Can For Serv For Tech Rep 33

Vega-García C, Chuvieco E (2006) Applying local measures of spatial heterogeneity to Landsat–TM images for predicting wildfire occurrence in Mediterranean landscapes. Landsc Ecol 21:595–605

Werth PA, Potter BE, Clements CB, Finney M, Goodrick SL, Alexander ME, Cruz MG, Forthofer JA, McAllister SS (2011) Synthesis of knowledge of extreme fire behavior: volume I for fire managers. Gen. Tech. Rep. PNW-GTR-854. Portland, OR: USDA, Forest Service, Pacific Northwest Research Station