atmosphere

Article Forest Fires in Madeira Island and the Fire Weather Created by Orographic Effects

Flavio T. Couto 1,2,*, Rui Salgado 1,2,3 and Nuno Guiomar 4

1 Instituto de Ciências da Terra—ICT (Polo de Évora), Universidade de Évora, Rua Romão Ramalho, 59, 7000-671 Évora, Portugal; [email protected] 2 Earth Remote Sensing Laboratory (EaRS Lab), Universidade de Évora, Rua Romão Ramalho, 59, 7000-671 Évora, Portugal 3 Departamento de Física, Escola de Ciências e Tecnologia, Universidade de Évora, Rua Romão Ramalho, 59, 7000-671 Évora, Portugal 4 MED—Mediterranean Institute for Agriculture, Environment and Development, Instituto de Investigação e Formação Avançada, Universidade de Évora, 7006-554 Évora, Portugal; [email protected] * Correspondence: [email protected]

Abstract: Understanding the effects of weather and topography on fire spread in specific contexts, such as oceanic islands, is critical for supporting fire prevention and suppression strategies. In this study, we analyse the atmospheric conditions associated with historical forest fires that have occurred over complex terrain in Madeira Island, Portugal. The atmospheric Meso-NH model was used to identify the mesoscale environment during three forest fires events. The model was configured into two nested horizontal domains, the outer domain at 2.5 km resolution and the inner domain at 500 m. The paper brings a comprehensive analysis on the factors favouring the evolution of significant large fires occurring in Madeira Island in August 2010, July 2012 and August 2016. These fire events were



 selected because they are characterized by their large size (between 324.99 ha and 7691.67 ha) that expanded in a short-time period, threatening people and property in the wildland-urban interfaces. Citation: Couto, F.T.; Salgado, R.; The study highlights that local terrain produce orographic effects that enhance the fire danger over Guiomar, N. Forest Fires in Madeira the southern slope during typical summer atmospheric conditions. Island and the Fire Weather Created by Orographic Effects. Atmosphere Keywords: fire weather; orographic effects; Madeira Island; Meso-NH model 2021, 12, 827. https://doi.org/ 10.3390/atmos12070827

Academic Editor: Jason C. Knievel 1. Introduction Received: 19 May 2021 The atmospheric circulation over complex terrain induces several meteorological Accepted: 25 June 2021 phenomena. The orographic effects may be triggered as air flows toward a mountain Published: 28 June 2021 barrier, depending on mountain shape and on its own flow regime. In general, it may be forced to flow upslope on the windward side and descend on the lee side, or still be Publisher’s Note: MDPI stays neutral blockaded or deviated by such an obstacle, depending on the dynamical and thermal with regard to jurisdictional claims in stability. In many mountainous regions, clouds and heavy precipitation development can published maps and institutional affil- be observed as result of complex interactions between air circulation and topography [1,2]. iations. Airflow crossing a mountain ridge may also produce other atmospheric phenomena with significant impacts at surface level. Diurnal mountain winds, dynamic channelling, foehn winds, low level jets or mountain waves are examples of orographic effects on airflow properties that can change their main characteristics (e.g., temperature, relative humidity, Copyright: © 2021 by the authors. wind speed and direction, atmospheric stability) and, in a context of fire propagation, also Licensee MDPI, Basel, Switzerland. change fire behaviour [3]. This article is an open access article In California, extreme fire events quickly spread following strong hot and dry winds, distributed under the terms and such as the Tubbs fire in October 2017 [4]. The fluctuations in climate conditions are another conditions of the Creative Commons factor that may contribute to unexpected wildfires [5]. The High Park wildfire in 2012 was Attribution (CC BY) license (https:// ignited under drought conditions just before an unseasonal downslope wind-storm [6], creativecommons.org/licenses/by/ characterized by extreme gusty surface winds that substantially increased fire spread rate. 4.0/).

Atmosphere 2021, 12, 827. https://doi.org/10.3390/atmos12070827 https://www.mdpi.com/journal/atmosphere Atmosphere 2021, 12, 827 2 of 22

Currently, one of the most relevant scientific challenges is to understand shifts in fire regimes, particularly related with the potential distribution of extreme fire events under the expected climate changes. In Australia, extreme wildfires are expected to be more frequent due to an increase in frequency of more hazardous fire weather conditions in many of the southern regions [7], as well as the expansion of the extreme wildfires season in the spring [8]. The same scenario is documented in several regions of the United States of America [9,10], already showing significant increasing trends of high severely burned areas across the south-west in all types of forest and woodland ecosystems [11]. It is well known that climate factors influence fire activity by determining fuel char- acteristics in the long-term, whereas the weather conditions affect fire behaviour in the short-term. However, the risk assessment of a potential intensification of wildfires from the expected changes in weather conditions is still a challenge worldwide, in particular due to the phenomena triggered by the interaction between fire and atmosphere that can create firestorms and unexpected fire behaviour [12,13]. In recent decades, fire modeling and simulation has evolved considerably, increas- ing its applicability in decision support both in fire prevention and fuel management contexts [14] and in the definition of fire suppression strategies and tactics [15]. Physically- based, empirical and semi-empirical models were developed and applied [16–19], as well as approaches and tools that couple fire surface models with fire-atmosphere models [20–22]. More recently, studies have been conducted to test and validate coupled fire-atmosphere models using real fire data [23] and to increase its operational capacity when integrated in fire spread forecasting systems [24]; to reduce uncertainty in fire spread predictions through real-time adjustments in fire simulation [25]; or to increase understanding on the interactive effects between different drivers on fire spread in high impact fires [26]. Efforts have also been dedicated to the use of convection-permitting simulation with an explicit electrical scheme to assess the current possibility of representing lightning phenomena during the early stages of forest fire development [27]. Lightning is the main natural fire ignition source around the globe [28], which often accumulates conditions for extreme fire propagation, especially after the disintegration of the cells creating local downdrafts characterized by strong and erratic winds. Besides the dry surface conditions, lightning strikes from thunderstorms in the dissipating stage were the dominant fire ignition source during the 2014 fire season in the Northwest regions of Canada [29]. Extreme fire events result in loss of life and property causing damages to the so- ciety [30]. The extensive study of different factors exacerbating extreme fire behaviour is critical to better understand how fire may be influenced by the atmospheric condi- tions, which may rapidly change and affect fire spread and intensity to thresholds above suppression capacity. In 2017, an extreme fire season affected Portugal and Spain. In Portugal, the first deadly event occurred in the region of Pedrógão Grande, causing more than 60 fatalities in June [27,31]. In late June, the forest fires in Southern Spain affected the Doñana Natural Park with a direct impact in biodiversity. The extreme meteorological conditions of temperature, relative humidity, and wind speed induced the rapid fire spread toward the Natural Park affecting many endangered plant and animal species [32]. Months later, on mid-October, extreme wildfires spread again across the Central region of Portugal mainland resulting in 48 fatalities [33]. Such extreme fire events contributed to the creation of the “Iberian Centre for Research and Forest Firefighting” (CILIFO, www.cilifo.eu, last accessed 17 May 2021), which has an operational framework covering the Portuguese regions of Alentejo and Algarve, as well as the Andalusia in Southern Spain. Both surface conditions, as terrain and fuel moisture, and atmospheric conditions, as high temperature and low relative humidity, are recognized as factors favouring forest fire occurrence and propagation [34]. Therefore, under the CILIFO framework, namely in the context of characterization of meteorological environments that favour the evolu- tion of significant large and extreme fires, this study aims to identify the atmospheric conditions associated with forest fires that have occurred in complex terrain landscapes Atmosphere 2021, 12, x FOR PEER REVIEW 3 of 23

Atmosphere 2021, 12, 827 3 of 22 as follows: Section 2 presents the study region and case studies, as well as the data used and numerical modelling aspects. In Section 3 the results are presented, which are sum- marizedof Madeira in IslandSection using 4 jointly convection-permitting with the conclusions. simulations. The paper is organized as follows: Section2 presents the study region and case studies, as well as the data used and 2.numerical Study Region, modelling Case aspects. Studies In Section and 3Numerical the results areModelling presented, which are summarized in Section4 jointly with the conclusions. 2.1. Study Region 2. StudyMadeira Region, is Casea Portuguese Studies and island Numerical located Modelling in the North Atlantic Ocean at 32°75 N and 2.1. Study Region 17°00 W (Figure 1). It is the largest island of the archipelago with approximately 740 km², ◦ withMadeira an east-west is a Portuguese elongated island form, located and a in central the North mountain Atlantic chain Ocean characterised at 32 75 N and by deep 17◦00 W (Figure1). It is the largest island of the archipelago with approximately 740 km 2, valleys, cliffs, and peaks up to above 1800 m in the eastern region. Such geography con- with an east-west elongated form, and a central mountain chain characterised by deep tributesvalleys, cliffs,to Madeira’s and peaks climate, up to defined above 1800 by dry m in summers the eastern and region. wet winters Such geography [35]. The precipi- tationcontributes is strongly to Madeira’s correlated climate, with defined the local by dryorography, summers as and observed wet winters in studies [35]. The during the winterprecipitation [36] and is strongly autumn correlated seasons with [37,38]. the localWhen orography, extreme, as the observed precipitating in studies events during may have athe significant winter [36 impact] and autumnat surface, seasons resulting [37,38 in]. flash When floods extreme, and thelandslides precipitating [39–41]. events In addition, themay mountains have a significant favour impact the development at surface, resulting of orogra inphic flash fogs floods throughout and landslides the year [39–41 [42–44],]. as wellIn addition, as dense the vegetation mountains [45]. favour Forest the developmentfires may be of observed orographic in fogsthe island throughout during the the sum- mertime.year [42–44 Forest], as well stands as dense cover vegetation 45% of [Madeira45]. Forest (34,044 fires may ha), be while observed shrubland in the island and natural during the summertime. Forest stands cover 45% of Madeira (34,044 ha), while shrubland grasslands cover 25% (24,255 ha), and extreme fire events pose a threat to these ecosystems and natural grasslands cover 25% (24,255 ha), and extreme fire events pose a threat to these andecosystems to local and economy to local economy[46]. [46].

Figure 1.1.Meso-NH Meso-NH configuration configuration and and Madeira Madeira island island location location with orography with orography obtained obtained from the from the SRTM database.database. (a ()a Outer) Outer domain domain at 2.5 at km2.5 resolution;km resolution; (b) Inner (b) domainInner domain at 500 m at resolution. 500 m resolution. 2.2. Case Studies (Historical Events) 2.2. Case Studies (Historical Events) In the last 15 years, the island was affected by several wildfires, some of them resulting in largeIn the burned last areas.15 years, Figure the2 islandshows thewas annual affected distribution by several of wildfires, the number some of fires of andthem result- ingburned in large areaaffecting burned forestareas. stands Figure and 2 shrublandshows the between annual 2000distribution and 2016. of The the years number 2010, of fires and2012 burned and 2016 area stand affecting out clearly forest from stands the remainingand shrubland years, between with more 2000 than and 6000 2016. ha ofThe years 2010,burnt forests2012 and and 2016 shrubland stand ([out47], clearly and Paulo from Fernandes—see the remaining acknowledgments). years, with more Thesethan 6000 ha ofthree burnt years forests were and then shrubland selected to ([47], be analysed and Paulo in terms Fernandes—see of fire weather acknowledgments). conditions. The These threeevents years occurred were in thethen following selected periods: to be 12analysed and 13 August in terms 2010; of18 fire and weather 19 July2012; conditions. and The 08–10 August 2016. events occurred in the following periods: 12 and 13 August 2010; 18 and 19 July 2012; and 08–10 August 2016. The satellite images presented in Figure 3 were obtained from the MODIS Aqua sat- ellite observations available in the NASA’s observatory website (accessed in December 2020). In each satellite image displayed in Figure 3, the active fires can be easily identified through the smoke being transported southward. The red line contour in Figure 3a shows that in Period 1 the forest fires occurred mainly in the Madeira highlands, namely over the central part of the island in the eastern peak. Figure 3b shows forest fires occurring in the extreme west and southern slope regions during Period 2, and in larger extension in

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the extreme east of the island. In Period 3, Figure 3c shows the fires on August 2016 in the southern slope. For this third period, Figure 3d shows the dimension of the burned areas which also affected the foothills of the island, namely the wildland-urban interface near Atmosphere 2021, 12, 827 4 of 22 the Funchal city in the south-eastern region, causing three fatalities, more than 300 houses destroyed, a thousand displaced people, and ~61 million EUR of damages [46].

FigureFigure 2. 2. AnnualAnnual distribution distribution of of the the number number of of fires fires and and burned burned area area affecting affecting forest forest patches patches and and shrublandshrubland between between 2000 2000 and and 2016. 2016. The The official official statisti statisticalcal data data presented presented here here did did not not count count the the total total burnedburned area, area, only only the the area area affected by firefire coveredcovered by by forest forest stands stands and and shrubland. shrubland. Data Source: source: [47] based for theon period official between statistics 2006 published and 2016; in [47 and] for Paulo the period Fernandes between for the 2006 period and 2016; between and Paulo2000 and Fernandes 2005 (see for acknowledgments).the period between 2000 and 2005 (see acknowledgments).

InThe fact, satellite these years images can presented be characterized in Figure by3 were a small obtained number from of large the MODIS and atypical Aqua satel-fires thatlite contributed observations to available most of in the the burned NASA’s area observatory (Table 1), website as can (accessedbe seen in in Figure December 4. These 2020). firesIn each spread satellite very image quickly displayed over a short in Figure period3, the of activetime, some fires can of which be easily resulted identified from through more thanthe smokeone ignition being (e.g., transported fire H in southward. Figure 4). The red line contour in Figure3a shows that in Period 1 the forest fires occurred mainly in the Madeira highlands, namely over the central part of the island in the eastern peak. Figure3b shows forest fires occurring in the extreme west and southern slope regions during Period 2, and in larger extension in the extreme east of the island. In Period 3, Figure3c shows the fires on August 2016 in the southern slope. For this third period, Figure3d shows the dimension of the burned areas which also affected the foothills of the island, namely the wildland-urban interface near the Funchal city in the south-eastern region, causing three fatalities, more than 300 houses destroyed, a thousand displaced people, and ~61 million EUR of damages [46]. In fact, these years can be characterized by a small number of large and atypical fires that contributed to most of the burned area (Table1), as can be seen in Figure4. These fires spread very quickly over a short period of time, some of which resulted from more than one ignition (e.g., fire H in Figure4).

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Figure 3. Satellite observations for each period considered in the study available in the NASA’s Figure 3. Satellite observations for each period considered in the study available in the NASA’s Atmosphere 2021, 12, x FOR PEER REVIEWobservatory website: (a) 13 August 2010 [48]; (b) 19 July 2012 [49], and (c) 08 August7 of 23 2016 [50]. observatory website: (a) 13 August 2010 [48]; (b) 19 July 2012 [49], and (c) 08 August 2016 [50]. (d) The(d burned) The burned area on area11 August on 11 2016 August [51]. 2016 [51].

The hotspots data from the MODIS and VIIRS sensors allowed dividing the target fires into periods (Table 1) and estimating the expansion rates in each of them. Addition- ally, we added some descriptive data for the Fire Radiative Power for each day, separating the measurements from the two sensors, since there are considerable differences between them. This previous assessment allowed the selection of the following periods to conduct the further analysis: (1) 12 and 13 August 2010 (Figure 3a); (2) 18 and 19 July 2012 (Figure 3b); (3) 08 to 10 August 2016 (Figure 3c). The satellite images presented in Figure 3 were obtained from the MODIS Aqua satellite observations available in the NASA’s observa- tory website (accessed in December 2020).

Figure 4. 4. Spatial distribution of the large fires occurred in 2010, 2012 and 2016. Source: Authors, Spatial distribution of the large fires occurred in 2010, 2012 and 2016. Source: Authors, based on on data data provided provided by by Paulo Paulo Fernandes Fernandes (see (seeacknowledgements); acknowledgements); Hillshade Hillshade was calculated was calculated us- using ing the SRTM 90 m DEM version 4. the SRTM 90 m DEM version 4. 2.3. Numerical Simulations and Model Validation The numerical simulations were performed using the Meso-NH, a non-hydrostatic model able to represent the atmospheric environments in different time and spatial scales, with a wide range of parametrization schemes for several physical processes observed in the Earth’s atmosphere [52,53]. Here, it was configured into two domains as shown in Figure 1. The outer domain was configured with 200 × 200 grid points and 2.5 km resolu- tion. To access the effects of the rugged local surface, an inner domain was designed with a resolution of 500 m (500 × 500 grid points), capable of better representing the complex terrain characteristic of the mountainous island. The vertical grid was calculated automat- ically by the model with a total of 50 levels following the terrain. The simulations were performed in a two-way interactive mode, initialized and forced using the European Cen- tre for Medium-Range Weather Forecasts (ECMWF) analysis updated each 6 h. In the present study, the convection-permitting simulations were performed with a parametrization configuration similar to those successfully used in previous studies over the island [37]. Namely, the radiation parametrization is based on the Rapid Radiative Transfer Model [54], whereas for the turbulence the 1D scheme [55] was used in the larger domain and the 3D scheme [56] in the smaller domain. The deep convection was assumed to be explicitly resolved and the shallow convection was parametrized only for the 2.5 km coarser domain [57]. The parametrization of cloud microphysics was made using the one- moment ICE3 scheme [58], which is able to represent five hydrometeor species for the water substance. Finally, the surface variables were obtained from the externalized SURFEX model coupled to the Meso-NH [59]. This configuration was applied for the three periods mentioned in Section 2.2. Each simulation starts on the day when the fires were ignited. For the first 12 h of each simula- tion, the model was run only over the larger domain, whereas in nested mode until the end of the experiment, i.e., 36 h for August 2010 and July 2012, and 60 h for August 2016.

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Table 1. Main characteristics of fire propagation on the target-days analysed. TBA: Total burned area by the large fires analysed; %ABA (F+S): Percentage of annual burned area covered by forest stands and shrubland (in relation to the official statistics provided in Figure2); FRP: Fire Radiative Power. Note: The daily expansion rates were estimated based on the fire hotspots data of MODIS and VIIRS sensors, and adjusted for each day.

FRP %ABA Daily Expansion Rate (ha/h) Year TBA MODIS (VIIRS) (F+S) Day Mean Max. N Mean P95 Max. 13/08 244.80 745.01 1234-1411UTC 75 144.2 680.1 1488.1 2010 8016.66 89.84% 14/08 165.80 324.48 0215-0353UTC 17 155.4 297.6 297.6 - - - - 16/07 2.46 7.61 0000-0359UTC (4) (2.7) (4.5) (4.5) 10 84.9 372.0 372.0 17/07 24.86 16.99 0340-1318UTC (9) (9.2) (15.3) (15.3) 38 102.4 364.8 432.3 18/07 82.09 102.70 0321-1440UTC (74) (18.4) (47.0) (142.8) 69 113.1 586.6 847.3 2012 6045.64 69.04% 19/07 172.95 290.37 0303-1421UTC (136) (31.1) (91.2) (157.0) 3 58.2 81.2 81.2 20/07 35.00 93.71 0000-0244UTC (90) (7.2) (41.4) (51.3) 7 60.7 264.5 264.5 21/07 17.20 18.80 0225-1343UTC (16) (4.0) (10.6) (10.6) 2 22.8 29.0 29.0 22/07 8.79 22.58 0206-0346UTC (11) (5.9) (13.4) (13.4) 22 101.6 265,1 554.4 8/08 60.80 88.61 1455-2400UTC (5) (30.9) (127.9) (127.9) 25 111.5 321.5 398.6 9/08 76.65 139.38 1436-2400UTC (101) (20.5) (146.0) (95.7) 54 80.9 204.5 293.6 2016 6246.25 91.79% 10/08 131.72 203.26 0259-1417UTC (185) (14.9) (55.7) (136.4) 17 98.3 519.5 519.5 11/08 29.92 40.86 0000-0240UTC (59) (15.1) (49.0) (69.8) 2 34.9 53.2 53.2 12/08 12.28 12.28 0000-0401UTC (15) (7.7) (20.3) (20.3)

The hotspots data from the MODIS and VIIRS sensors allowed dividing the target fires into periods (Table1) and estimating the expansion rates in each of them. Additionally, we added some descriptive data for the Fire Radiative Power for each day, separating the measurements from the two sensors, since there are considerable differences between them. This previous assessment allowed the selection of the following periods to conduct the further analysis: (1) 12 and 13 August 2010 (Figure3a); (2) 18 and 19 July 2012 ( Figure3b ); (3) 08 to 10 August 2016 (Figure3c). The satellite images presented in Figure3 were obtained from the MODIS Aqua satellite observations available in the NASA’s observatory website (accessed in December 2020).

2.3. Numerical Simulations and Model Validation The numerical simulations were performed using the Meso-NH, a non-hydrostatic model able to represent the atmospheric environments in different time and spatial scales, with a wide range of parametrization schemes for several physical processes observed in the Earth’s atmosphere [52,53]. Here, it was configured into two domains as shown in Figure1. The outer domain was configured with 200 × 200 grid points and 2.5 km resolution. To access the effects of the rugged local surface, an inner domain was designed with a resolution of 500 m (500 × 500 grid points), capable of better representing the complex terrain characteristic of the mountainous island. The vertical grid was calculated automatically by the model with a total of 50 levels following the terrain. The simulations were performed in a two-way interactive mode, initialized and forced using the European Centre for Medium-Range Weather Forecasts (ECMWF) analysis updated each 6 h. Atmosphere 2021, 12, 827 7 of 22

In the present study, the convection-permitting simulations were performed with a parametrization configuration similar to those successfully used in previous studies over the island [37]. Namely, the radiation parametrization is based on the Rapid Radiative Transfer Model [54], whereas for the turbulence the 1D scheme [55] was used in the larger domain and the 3D scheme [56] in the smaller domain. The deep convection was assumed to be explicitly resolved and the shallow convection was parametrized only for the 2.5 km coarser domain [57]. The parametrization of cloud microphysics was made using the one-moment ICE3 scheme [58], which is able to represent five hydrometeor species for the water substance. Finally, the surface variables were obtained from the externalized SURFEX model coupled to the Meso-NH [59]. This configuration was applied for the three periods mentioned in Section 2.2. Each simulation starts on the day when the fires were ignited. For the first 12 h of each simulation, the model was run only over the larger domain, whereas in nested mode until the end of the experiment, i.e., 36 h for August 2010 and July 2012, and 60 h for August 2016. Such a configuration was chosen in order to assess the prevailing weather conditions encompassing the fire events. The interactions between the fires and the atmosphere were not taken into account in the experiments. The model validation is made from a point to point comparison between observed and simulated time series. The meteorological variables verified were wind gusts, wind direction, air temperature at 2 m, and relative humidity at 2 m. Figure5 shows some plots for three different meteorological stations: Areeiro (latitude: 32.72, longitude: −16.91), Ponta do Pargo (latitude: 32.81, longitude: −17.26) and Funchal (latitude: 32.64, longitude: −16.89). Such a comparison was applied for the three events considered in the study. For the most significant event, which occurred in August 2016, Figure5a shows that the model well captures the wind gusts in the Madeira highlands (Areeiro station), as well as the air temperature behaviour during the period (Figure5b). In the Ponta do Pargo station (Figure5c), the wind gusts are overestimated by the model in the first 24 h of simulation, but the temporal behaviour is well represented. In Funchal station, a similar result is found with a good representation of the wind pattern, but with the wind gusts being somewhat overestimated by the model during the entire period (Figure5d). On the other hand, and despite some discrepancy in the last hours of the simulation, very good results are obtained for the air temperature and relative humidity at 2 m, (see Figure5e,f, respectively for Funchal). The high air temperature in Funchal, above 35 ºC, is slightly overestimated by the model (Figure5e), whereas the very low relative humidity values around 15% are well simulated by the model (Figure5f). The comparisons for the other two episodes also show the ability of the model in reproducing the weather evolution, although the point-by-point comparison revealed greater differences, partially due to local effects, more visible in lighter wind situations. We select two examples. For the episode in 2012, Figure5g indicates that the model well captures the air temperature in the Madeira highlands (Areeiro station). In the same Areeiro station (Figure5h), the model also captures the air temperature behaviour along the 2010 period, but with a significant underestimation of the observed values. The higher observed temperatures may be a consequence of the wildfire that occurred precisely in this region, whose effects were not taken into account by the model. AtmosphereAtmosphere 20212021, 12, 12, x, 827FOR PEER REVIEW 9 of8 of23 22

FigureFigure 5. 5.Time(a)–( seriesh) represent point to time point series comparison point to point between comparison observations between and observations simulations and at 500 simula- m horizontaltions at 500 resolution. m horizontal resolution. 3. Results

3.1. Synoptic Environment The sea level pressure and wind vectors at 1000 mb are shown in Figure6 representing the large scale circulation during the first day of each episode. The fields of sea level pressure and wind vectors at 1000 mb have a uniform latitude-longitude 2.5◦ resolution grid [60] and were used to identify the synoptic situation near the surface. The data was obtained from the 6-hourly NCEP/NCAR Reanalysis Data Composites [61]. On 12 August

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3. Results

3.1. Synoptic Environment The sea level pressure and wind vectors at 1000 mb are shown in Figure 6 represent- ing the large scale circulation during the first day of each episode. The fields of sea level Atmosphere 2021, 12, 827 pressure and wind vectors at 1000 mb have a uniform latitude-longitude 2.5° resolution9 of 22 grid [60] and were used to identify the synoptic situation near the surface. The data was obtained from the 6-hourly NCEP/NCAR Reanalysis Data Composites [61]. On 12 August 2010, corresponding to the first period, Figure 6a shows the Azores’s Anticyclone centred 2010, corresponding to the first period, Figure6a shows the Azores’s Anticyclone centred at 52° N and 20° W. Near the surface, the associated circulation favours north-easterly at 52◦ N and 20◦ W. Near the surface, the associated circulation favours north-easterly winds over the island. The episode that occurred in July 2012 is also linked to the presence winds over the island. The episode that occurred in July 2012 is also linked to the presence of an anticyclone system over the North Atlantic Ocean (Figure 6b). It is centred at around of an anticyclone system over the North Atlantic Ocean (Figure6b). It is centred at around 35° N and 30° W, but still induces north-easterly winds, although northerly winds could 35◦ N and 30◦ W, but still induces north-easterly winds, although northerly winds could rule over the island of Madeira. For the third period, namely in August 2016, a large-scale rule over the island of Madeira. For the third period, namely in August 2016, a large-scale configuration similar to the first episode can be observed in Figure 6c, i.e., the Azores configuration similar to the first episode can be observed in Figure6c, i.e., the Azores anticyclone centred in higher latitudes (53° N and 25° W) which lead to north-easterly anticyclone centred in higher latitudes (53◦ N and 25◦ W) which lead to north-easterly winds affecting the island. winds affecting the island.

FigureFigure 6. 6. SeaSea level level pressure pressure and and wind wind vectors vectors at at 1000 1000 mb mb at at 1200 1200 UTC UTC on on ( (aa)) 12 12 August August 2010; 2010; ( (bb)) 18 18 JulyJuly 2012 2012 and and (c (c) )08 08 August August 2016. 2016. Source: Source: [61]. [61].

3.2.3.2. Mesoscale Mesoscale Environment Environment and and Fire Fire Weather Weather Conditions Conditions ForFor each each period, period, simulations simulations at 500 mm horizontalhorizontal resolutionresolution were were conducted conducted to to identify iden- tifythe the meteorological meteorological conditions conditions that that influenced influenced the developmentthe development of the of abovethe above mentioned men- tionedlarge fires. large Each fires. section Each section begins begins with the with results the forresults the airflowfor the affectingairflow affecting the island, the followed island, followedby the analysis by the ofanalysis the air of temperature the air temperat and relativeure and humidity relative humidity fields at 2fields m. at 2 m.

3.2.1.3.2.1. Period Period 1: 1: 12 12 and and 13 13 August August 2010 2010 TheThe north-easterly north-easterly flow flow affecting affecting the the island island identified identified in in Figure Figure 6 was analysed for eacheach period period aiming aiming to to determine determine the the wind wind in intensitytensity from from the the high-resolution high-resolution simulations. simulations. TheThe vertical vertical profiles profiles in in Figure Figure 7 were obtainedobtained at the points A, B and C indicated in the bottombottom of of the the Figure Figure 77.. OnOn thethe firstfirst day,day, the the winds winds affecting affecting the the Point Point A A present present an an intensity inten- weaker than 11 m/s in the lower troposphere (Figure7a) and are less intense as they sity weaker than 11 m/s in the lower troposphere (Figure 7a) and are less intense as they approach the island (Point B; Figure7b). At Point A, the vertical profiles in Figure7d,g approach the island (Point B; Figure 7b). At Point A, the vertical profiles in Figure 7d,g show an intensification of the airflow during the night and following day, respectively. show an intensification of the airflow during the night and following day, respectively. The airflow around 1500 m present velocities around 15 m/s (Figure7d) and 16.5 m/s The airflow around 1500 m present velocities around 15 m/s (Figure 7d) and 16.5 m/s (Fig- (Figure7g ). The mountain effect over Point B (Figure7e,h) is also evident, with weak winds ure 7g). The mountain effect over Point B (Figure 7e,h) is also evident, with weak winds near the surface rapidly increasing in magnitude up to the top of the island around 1500 m. near the surface rapidly increasing in magnitude up to the top of the island around 1500 On the lee side of the island, Point C, there is a stagnation of large-scale circulation m. close to the surface, with a minimum in wind speed at about 800 m (Figure7c,f,i). This On the lee side of the island, Point C, there is a stagnation of large-scale circulation stagnation creates conditions for the development of a local thermal circulation, a sea close to the surface, with a minimum in wind speed at about 800 m (Figure 7c,f,i). This breeze that is maintained even during nighttime, which increases the wind speed towards stagnation creates conditions for the development of a local thermal circulation, a sea the island in the first several hundreds of meters close to the surface.

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Atmosphere 2021, 12, 827 10 of 22 breeze that is maintained even during nighttime, which increases the wind speed towards the island in the first several hundreds of meters close to the surface.

Figure 7. Vertical profile of horizontal wind velocity simulated at 500m resolution for Period 1. Figure 7. Vertical profile of horizontal wind velocity simulated at 500m resolution for Period 1. (a,d,g) for Point A (latitude: 33.05, longitude: −16.65), whereas (b,e,h) for Point B (latitude: 32.87, (longitude:a,d,g) for Point−16.87), A (latitude:and (c,f,i) 33.05,for Point longitude: C (latitude:−16.65), 32.58, whereas longitude: (b, e−,17.15).h) for Point B (latitude: 32.87, longitude: −16.87), and (c,f,i) for Point C (latitude: 32.58, longitude: −17.15). As a consequence of such circulation affecting the island, weak wind gusts were sim- As a consequence of such circulation affecting the island, weak wind gusts were ulated over a large part of Madeira (<15 m/s) during the afternoon of 12 August (Figure simulated over a large part of Madeira (<15 m/s) during the afternoon of 12 August 8a). The condition intensified overnight (Figure 8b) with wind gusts higher than 22 m/s in (Figure8a). The condition intensified overnight (Figure8b) with wind gusts higher than the mountains top. The situation remains during the second day with wind gusts higher 22 m/s in the mountains top. The situation remains during the second day with wind than 20 m/s over the highlands in the central part of the island (Figure 8c). Such a condi- gusts higher than 20 m/s over the highlands in the central part of the island (Figure8c). tion favoured fire spread in the Madeira highlands over the eastern peak (see Figure 3a). Such a condition favoured fire spread in the Madeira highlands over the eastern peak Additionally, the figures reveal the establishment of two low-level tip-jets, near the east (see Figure3a ). Additionally, the figures reveal the establishment of two low-level tip-jets, near the east and west flanks of the island, which is a frequent feature during the summer atmospheric flow over Madeira Island [62]. The figure also shows vectors representing the

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Atmosphere 2021, 12, 827 and west flanks of the island, which is a frequent feature during the summer atmospheric11 of 22 and west flanks of the island, which is a frequent feature during the summer atmospheric flow over Madeira Island [62]. The figure also shows vectors representing the wind at 500 flow over Madeira Island [62]. The figure also shows vectors representing the wind at 500 m altitude, which indicate that below 1 km altitude the north-easterly flow was forced to m altitude, which indicate that below 1 km altitude the north-easterly flow was forced to windgo around at 500 mthe altitude, island. whichIt was indicate determined that belowthere 1was km a altitude decrease the in north-easterly wind intensity flow as was the goairflow around approached the island. the It island,was determined extending therovere thewas ocean a decrease near to in the wind northern intensity coastal as zonethe airflowforced toapproached go around the the island, island. extending It was determined over the thereocean was near a decreaseto the northern in wind coastal intensity zone as the(smallest airflow arrows). approached The mountain the island, effect extending on the over airflow the oceancan also near be toseen the over northern the ocean coastal to (smallest arrows). The mountain effect on the airflow can also be seen over the ocean to zonethe south-westward (smallest arrows). corresponding The mountain toeffect a decrease on the in airflow wind intensity can also beand seen the overinversion the ocean of its the south-westward corresponding to a decrease in wind intensity and the inversion of its todirection the south-westward close to the surface, corresponding due to the to devel a decreaseopment in of wind the sea intensity breeze, and as theseen inversion in Figure direction close to the surface, due to the development of the sea breeze, as seen in Figure of7c,f,i. its directionThese effects close at to the the lowest surface, levels due we tore the maintained development throughout of the sea the breeze, period, as and seen even in 7c,f,i. These effects at the lowest levels were maintained throughout the period, and even Figurefollowed7c,f,i. slight These changes effects in at flow the lowest direction. levels were maintained throughout the period, and followed slight changes in flow direction. even followed slight changes in flow direction.

FigureFigure 8.8. (Winda)–(c) representgusts at 10 wind m simulated gusts at 10by m the simulated inner domain by the during inner domain Period during1 (filled Period contours). 1 (filled The Figureline contours 8. Wind over gusts the at 10island m simulated represent by the the elevat innerion domain in each during 500 m Pealtitude.riod 1 (filledThe arrows contours). represent The contours). The line contours over the island represent the elevation in each 500 m altitude. The linethe contours mean wind over at the500 islandm altitude represent (m/s). the elevation in each 500 m altitude. The arrows represent thearrows mean represent wind at the500 meanm altitude wind (m/s). at 500 m altitude (m/s).

Figure 9a show the air temperature field at 2 m with values above 32◦ °C along the FigureFigure 99aa show the air temperature fieldfield at 2 mm withwith valuesvalues aboveabove 3232 °CC along along the the southernsouthern slopesslopes andand aboveabove 3434 ◦°CC inin otherother areas,areas, namelynamely wherewhere thethe wildfireswildfires occurred.occurred. southernNotice that slopes the atmosphericand above 34 model °C in doesother not areas, take namely fire effects where into the account. wildfires At night,occurred. tem- NoticeNotice that that the atmospheric modelmodel does does not not take take fire fire effects effects into into account. account. At At night, night, tempera- tem- peratures above◦ 26 °C were simulated on the southern slopes, namely in the landscapes peraturestures above above 26 C26 were °C were simulated simulated on the on southern the southern slopes, slopes, namely namely in the landscapesin the landscapes located atlocated the middle at the elevations middle elevations (Figure9b). (Figure On the 9b). second On day,the second the temperatures day, the temperatures were milder thanwere locatedmilder atthan the themiddle first elevationsday, with maximums(Figure 9b). on On the the southern second day,slopes◦ the around temperatures 32 °C (Figure were milderthe first than day, the with first maximums day, with on maximums the southern on slopes the southern around 32slopesC (Figure around9c). 32 The °C squares(Figure represent9c). The squares the temperature represent the at the temperature meteorological at the stations.meteorological The simple stations. comparison The simple shows com- 9c). The squares represent the temperature at the meteorological stations. The simple com- thatparison the modelshows wellthat representsthe model well the temperature represents the near temperature the surface, near even the with surface, some even punctual with parison shows that the model well represents the temperature near the surface, even with overestimationsome punctual (Figureoverestimation9c). (Figure 9c). some punctual overestimation (Figure 9c).

FigureFigure 9.9. (Relativea)–(c) represent humidity air at temperature 2 meters simulated at 2 m simulated at 500 m atresolution 500 m resolution during the during Period the 1. Period The line 1. FigureThecontours line 9. contoursRelative over the overhumidity island the islandrepresent at 2 meters represent the simulated elevation the elevation atin 500each in m each500 resolution m 500 altitude. maltitude. during The the Thesquares Period squares represent 1. representThe line the contours over the island represent the elevation in each 500 m altitude. The squares represent the theobservations observations at the at themeteorological meteorological stations. stations. observations at the meteorological stations. ConcerningConcerning thethe relative humidity at at 2 2 m m (Figure (Figure 10), 10), values values below below 20% 20% were were deter- de- terminedminedConcerning over over a large a the large partrelative part of the of humidity the island island on at 12 on2 m August 12 (Figure August (Figure 10), (Figure values 10a), 10 belowdecreasinga), decreasing 20% towere ~15% to deter- ~15% near minednearFunchal Funchal over (see a largeFigure (see part Figure 1a forof1 thethea for islandlocation). the location).on 12The August relative The (Figure relativehumidity 10a), humidity remained decreasing remained low to on ~15% the low south- near on Funchaltheern southernslopes (see at Figure night, slopes 1a showing at for night, the valueslocation). showing below The values 25% relative belowin most humidity 25% parts in ofremained most the partsmidlands low of theon (Figure the midlands south- 10b). ern(FigureOn slopes 13 August 10 atb). night, On (Figure 13 showing August 10c), valuesvalues (Figure belowof 10 aroundc), 25% values 20%in most of were around parts simulated 20%of the were midlands over simulated the central(Figure over part 10b). the of Oncentralthe 13 island, August part with of (Figure the some island, 10c),minimums withvalues some aroundof around minimums 15% 20% in the aroundwere southern simulated 15% slope. in theover The southern the comparison central slope. part Thewith of thecomparison island, with with some the minimums meteorological around stations 15% in show the southern a good representation slope. The comparison (Figure 10 witha,b), with an underestimation of the relative humidity near the southern coast in Figure 10c.

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Atmosphere 2021, 12, 827 12 of 22 thethe meteorological meteorological stations stations show show a agood good repr representationesentation (Figure (Figure 10a,b), 10a,b), with with an an underesti- underesti- mationmation of of the the relative relative humidity humidity near near the the southern southern coast coast in in Figure Figure 10c. 10c.

FigureFigureFigure 10. 10. Relative Relative(a)–(c) representhumidity humidity relative at at 2 2m m humiditysimulated simulated at at 2at m500 500 simulated m m resolution resolution at 500 during mduring resolution th the ePeriod Period during 1. 1. theThe The Period line line contours over the island represent the elevation in each 500 m altitude. The squares represent the contours1. The lineover contours the island over represent the island the elevation represent in the each elevation 500 m inaltitude. each 500 The m squares altitude. represent The squares the observations at the meteorological stations. observationsrepresent the at observationsthe meteorological at the meteorologicalstations. stations.

FigureFigureFigure 11 1111 shows showsshows a a avertical vertical vertical cross-section cross-section cross-section (displayed (displayed (displayed in in Figure Figure Figure 11b) 11b)11b) of of of the the the vertical vertical vertical wind wind wind speedspeedspeed over over over the the the eastern eastern eastern part part part of of of the the the island. island. island. Figure Figure Figure 11a 11a11 aindicates indicates indicates that that that the the the dominant dominant dominant effect effect effect of of thethethe island island island in in in deviating deviating deviating the the the airflow airflow airflow was was was not not not the the the unique unique unique effect effect effect and, and, and, around around around 1km 1km 1km altitude, altitude, altitude, the the the airflowairflowairflow was was was forced forced forced to to to go go go over over over the the the island island island through through through the the the highlands highlands highlands of of the the the northern northern northern slopes. slopes. This This This effecteffecteffect reinforced reinforced reinforced the the the noteworthy noteworthy noteworthy intense intense intense downward downward downward motion motion in in the the southern southern southern slopes slopes and and the the the effecteffecteffect of of of the the the gravity gravity gravity waves waves waves extending extending extending southward. southward. southward.

Figure 11. South-west to north-east vertical cross section of vertical velocity (coloured areas) cross- FigureFigure 11. 11. South-westSouth-west to to north-east north-east vertical vertical cross cross section section of of vertical vertical velocity (coloured areas)areas) crossingcross- ing the eastern part of the island and potential temperature (black lines) (a) 0400 UTC-13 August ingthe the eastern eastern part part of of the the island island and and potential potential temperature temperature (black (black lines) lines) (a) 0400(a) 0400 UTC-13 UTC-13 August August 2010, 2010,2010, ( b(b) )0000 0000 UTC-19 UTC-19 July July 2012, 2012, and and ( c()c )0000 0000 UTC-09 UTC-09 August August 2016. 2016. The The localization localization of of the the cross cross (b) 0000 UTC-19 July 2012, and (c) 0000 UTC-09 August 2016. The localization of the cross section is sectionsection is is indicated indicated in in the the inner inner figure figure in in (b (b). ). indicated in the inner figure in (b). 3.2.2. Period 2: 18 and 19 July 2012 3.2.2.3.2.2. Period Period 2: 2:18 18 and and 19 19 July July 2012 2012 Figure 12 displays the vertical profile of the wind module at three points over the FigureFigure 12 12 displays displays the the vertical vertical profile profile of of the the wind wind module module at at three three points points over over the the ocean (Points A, B and C at the bottom of the Figure 7) for the selected hours of Period 2. oceanocean (Points (Points A, A, B Band and C Cat atthe the bottom bottom of of the the Figure Figure 7)7 )for for the the selected selected hours hours of of Period Period 2. 2. TheTheThe maximum maximum maximum wind wind wind speed speed of of almost almost 11 11 m/ m/sm/s swas was was simulated simulated simulated between between between 500 500 500 m m m and and and 1500 1500 1500 m m altitudealtitudealtitude during during during the the the afternoon afternoon afternoon of of ofthe the the 18 18 July 18 July July (F (Figureigure (Figure 12a). 12a). 12 Closea). Close Close to to the the to northern thenorthern northern part part of part of the the of island,island,the island, still still over stillover the over the ocean ocean the ocean (Point (Point (Point B), B), the the B), vertical vertical the vertical profile profile profile of of the the of wind wind the windmodule module module shows shows shows a ade- de- a creasecreasedecrease in in the inthe theintensity intensity intensity of of the ofthe theairflow airflow airflow as as asit it approached itapproached approached the the the island, island, island, with with with winds winds of of 2.5 2.52.5 m/s m/sm/s belowbelowbelow 500 500 500 m m maltitude altitude altitude (Figure (Figure (Figure 12b). 12b). 12 Thereb). There There was was a was aslight slight a slight intensification intensification intensification of of this this ofcondition, condition, this condition, with with windswindswith of winds of 11 11 m/s m/s of at 11 at 800 m/s800 m m ataltitude, altitude, 800 m at altitude, at 0000 0000 UTC UTC at 0000 (Figure (Figure UTC 12d). 12d). (Figure At At Point Point12d). B, B, Atwinds winds Point reached reached B, winds a a minimumminimumreached alesser minimumlesser than than 2.5 lesser 2.5 m/s m/s than near near 2.5 the the m/s surface surface near (Figure the (Figure surface 12e). 12e). (Figure On On 19 19 12July, July,e). Onthe the 19wind wind July, intensity intensity the wind affectingaffectingintensity the affectingthe island island thedecreased decreased island decreased and and during during and th duringthe eafternoon afternoon the afternoon (Figure (Figure (Figure12g); 12g); for 12for g);example, example, for example, the the maximummaximumthe maximum wind wind windintensity intensity intensity at at 600 600 atm m 600was was m below below was below10 10 m/s. m/s. 10 Close Close m/s. to to Closethe the isla isla tond thend (Point (Point island B; B; (PointFigure Figure B; 12h),12h),Figure a adecrease decrease12h), a decreaseof of airflow airflow of intensity airflowintensity intensity was was noticed, noticed, was noticed,mainly mainly near mainlynear the the nearsurface. surface. the surface.

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Atmosphere 2021, 12, 827 As in Period 1, Figure 12c,i together with the vertical profile of horizontal wind13 of di- 22 rections (Figure S1a,b of the Supplementary material) show the existence of a sea breeze circulation during the afternoon.

Figure 12. As Figure 77,, butbut forfor PeriodPeriod 2.2.

TheAs insimulated Period 1, wind Figure gusts 12c,i at together10m reached with values the vertical around profile 15 m/s of at horizontal the top of wind the islanddirections in the (Figure central S1a,b area of (Figure the Supplementary 13a) and were Material) slightly stronger show the at existence 0000 UTC of (Figure a sea breeze 13b). Thecirculation model duringrevealed the a afternoon.gradual decreasing of the wind gusts during 19 July (Figure 13c). However,The simulated it is noteworthy wind guststhat the at 10mmodel reached simulated values wind around gusts 15above m/s 17 at m/s the in top the of east- the ernisland and in especially the central in area the western (Figure 13 regions,a) and wereassociated slightly with stronger the low-level at 0000 tip-jets. UTC (Figure These 13 rel-b). ativelyThe model higher revealed gusts occurred a gradual in decreasingthe areas most of the affected wind by gusts wildfires during (see 19 Figure July (Figure 3b). Figure 13c). 13However, also shows it is noteworthythat the airflow that reaching the model the simulated island was wind predominantly gusts above 17 from m/s the in thenorth-east eastern and especially in the western regions, associated with the low-level tip-jets. These relatively along the period throughout the lower troposphere. In this case, the mountain effect was higher gusts occurred in the areas most affected by wildfires (see Figure3b). Figure 13 more evident in the lowest levels where the airflow was deviated by the island (Figure also shows that the airflow reaching the island was predominantly from the north-east 13). The decreasing of the airflow as it approached and go around the island was seen along the period throughout the lower troposphere. In this case, the mountain effect was over the ocean along the northern coastal region. Concerning the vertical speed, Figure more evident in the lowest levels where the airflow was deviated by the island (Figure 13). The decreasing of the airflow as it approached and go around the island was seen over the ocean along the northern coastal region. Concerning the vertical speed, Figure 11b shows relatively strong downward motion in the southern slopes and upward motion in Atmosphere 2021, 12, x FOR PEER REVIEW 15 of 23

11b shows relatively strong downward motion in the southern slopes and upward motion in the northern ones above 800 m altitude, also indicating that the airflow tends to go around the island at the lowest levels.

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Atmosphere 2021, 12, 827 14 of 22

11b11b showsshows relativelyrelatively strongstrong downwarddownward motionmotion inin thethe southernsouthern slopesslopes andand upwardupward motionmotion in the northern ones above 800 m altitude, also indicating that the airflow tends to go inthe the northern northern ones ones above above 800 m800 altitude, m altitude, also indicatingalso indicating that the that airflow the airflow tends to tends go around to go aroundaroundthe island thethe at islandisland the lowest atat thethe levels. lowestlowest levels.levels.

Figure 13. As Figure 8, but for Period 2.

Figure 14a shows air temperatures at 2 m above 30 °C on the southern slopes, as well as maximum temperatures above 34 °C in the south-eastern part of the island. At night, milder temperatures around 25 °C were simulated in the highlands of the southern slopes, as well as 30 °C in the south-eastern foothill of the island (Figure 14b). In the early after- noon, at 1400 UTC, temperatures above 30 °C and a maximum of 34 °C in the south-east- FigureFigure 13. 13. As Figure 8, but for Period 2. Figureern part 13. of As the Figure island 88,, butbut were forfor Period Periodsimulated, 2.2. but in a lesser extension (Figure 14c). The model well Figurerepresents 14a the shows spatial air temperaturesdistribution of at the 2 mtemperature above 30 ◦ Cnear on surface the southern when compared slopes, as FigureFigure 14a14a showsshows airair temperaturestemperatures atat 22 mm aboveabove 3030 °C°C onon thethe southernsouthern slopes,slopes, asas wellwell wellwith asthe maximum observations temperatures available during above the 34 ◦period.C in the south-eastern part of the island. At asas maximummaximum temperaturestemperatures aboveabove 3434 °C°C inin thethe south-easternsouth-eastern partpart ofof thethe island.island. AtAt night,night, night,For milder the relative temperatures humidity around field 25 at◦ C2 m, were we simulated obtained invalues the highlands below 30% of theover southern a large mildermilder temperaturestemperatures around around 2525 °C°C werewere simulated simulated inin thethe highlandshighlands of of thethe southern southern slopes,slopes, partslopes, of the as wellsouthern as 30 slopes◦C in (Figure the south-eastern 15a), with foothillno changes of the during island the (Figure night (Figure14b). In 15b). the asas wellwell asas 3030 °C°C inin thethe south-easternsouth-eastern foothillfoothill ofof thethe islandisland (Figure(Figure 14b).14b). InIn thethe earlyearly after-after- Figureearly afternoon, 15c shows at a 1400 decrease UTC, of temperatures relative humidi abovety in 30 the◦C andsecond a maximum day, with of values 34 ◦C below in the noon,noon, atat 14001400 UTC,UTC, temperaturestemperatures aboveabove 3030 °C°C andand aa maximummaximum ofof 3434 °C°C inin thethe south-east-south-east- 20%south-eastern in the central part part of the of the island island were and simulated, a minimum but lesser in a than lesser 10% extension in the south-eastern (Figure 14c). ernern partpart ofof thethe islandisland werewere simulated,simulated, butbut inin aa lesserlesser extensionextension (Figure(Figure 14c).14c). TheThe modelmodel Theregion. model In general, well represents the comparisons the spatial with distribution observations of show the temperature that the model near well surface represents when wellwell representsrepresents thethe spatialspatial distributiondistribution ofof thethe temperaturetemperature nearnear surfacesurface whenwhen comparedcompared thecompared relative with humidity the observations field near surface. available during the period. withwith thethe observationsobservations availableavailable duringduring thethe period.period. ForFor thethe relativerelative humidityhumidity fieldfield atat 22 m,m, wewe obtainedobtained valuesvalues belowbelow 30%30% overover aa largelarge partpart ofof thethe southernsouthern slopesslopes (Figure(Figure 15a),15a), withwith nono changeschanges duringduring thethe nightnight (Figure(Figure 15b).15b). FigureFigure 15c15c showsshows aa decreasedecrease ofof relativerelative humidihumidityty inin thethe secondsecond day,day, withwith valuesvalues belowbelow 20%20% inin thethe centralcentral partpart ofof thethe islandisland andand aa minimumminimum lesserlesser thanthan 10%10% inin thethe south-easternsouth-eastern region.region. In In general, general, the the comparisons comparisons with with observ observationsations show show that that the the model model well well represents represents thethe relativerelative humidityhumidity fieldfield nearnear surface.surface.

Figure 14. As Figure 9, but for Period 2. Figure 14. As Figure9, but for Period 2.

For the relative humidity field at 2 m, we obtained values below 30% over a large part of the southern slopes (Figure 15a), with no changes during the night (Figure 15b). Figure 15c shows a decrease of relative humidity in the second day, with values below 20% in the central part of the island and a minimum lesser than 10% in the south-eastern region. FigureIn general, 14. As theFigure comparisons 9, but for Period with 2. observations show that the model well represents the Figurerelative 14. humidity As Figure field 9, but near for Period surface. 2.

Figure 15. As Figure 10, but for Period 2.

3.2.3. Period 3: 08 to 10 August 2016 In Figure 16a, the vertical wind profile at Point A shows that the airflow approaching the island reached an intensity above 15 m/s on 08 August. The results show that the

FigureFigure 15. 15. AsAs FigureFigure 10,10,10, butbut for for Period Period 2. 2. 3.2.3. Period 3: 08 to 10 August 2016 3.2.3.3.2.3. PeriodPeriod 3:3: 0808 toto 1010 AugustAugust 20162016 In Figure 16a, the vertical wind profile at Point A shows that the airflow approaching InIn FigureFigure 16a,16a, thethe verticalvertical windwind profileprofile atat PointPoint AA showsshows thatthat thethe airflowairflow approachingapproaching the island reached an intensity above 15 m/s on 08 August. The results show that the winds thethe islandisland reachedreached anan intensityintensity aboveabove 1515 m/sm/s onon 0808 August.August. TheThe resultsresults showshow thatthat thethe start to decrease in intensity from the morning of 09 August. The wind intensity around 12 m/s were verified in the afternoon at 1000 m altitude (Figure 16d), and decreasing

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winds start to decrease in intensity from the morning of 09 August. The wind intensity around 12 m/s were verified in the afternoon at 1000 m altitude (Figure 16d), and decreas- ingin intensity in intensity and and altitude altitude on on 10 10 August August (Figure (Figure 16 16g),g), showing showing wind wind speed speed of of 10 10 m/s m/s in thethe afternoon afternoon and and below 500 m altitude (Figure 16g).16g). At Point B, the mountain effect in lowestlowest levels levels of of the the wind wind field field is is evident evident in in a allll the the vertical vertical profiles profiles during during the the entire entire period, period, with weak winds being simulated up to 500 m al altitudetitude (Figure 16b,e,h)16b,e,h),, but with no effect or even a slight increase betweenbetween 1 and 2 km aboveabove seasea surface.surface. Contrary to what was identifiedidentified in in Periods Periods 1 1 and and 2, 2, Figure Figure 16c,e,f, 16c,f,ii dodo notnot containcontain aa signaturesignature ofof the occurrence of a local sea breeze near the south coast, certainlycertainly linked to the fact that the mountain downward flow flow extends along the entire slope to near the coast (Figure 1111c).c).

Figure 16. AsAs Figure Figure 77,, butbut forfor PeriodPeriod 3.3.

The wind gusts at 10 m are shown in Figure 1717a–f.a–f. Figure 17a–c17a–c show extreme gusts over the the island island with with speeds speeds above above 25 25 m/s m/s and and maximum maximum above above 30 m/s, 30 m/s, mainly mainly in the in cen- the tralcentral region region and andthe thesouth-eastern south-eastern part partof the of island. the island. Maximums Maximums exceeding exceeding 25 m/s 25 were m/s observedwere observed in the insouthern the southern slopes slopes near Funchal near Funchal where where one of one the of large the largefires firesoccurred occurred (See (See Figure3c,d ). Wind loses intensity along the day (Figure 17d,e); however, intense wind gusts were still simulated in the west and south-eastern parts of the island. During

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Figure 3c,d). Wind loses intensity along the day (Figure 17d–e); however, intense wind gusts were still simulated in the west and south-eastern parts of the island. During 10 August, there were no records of significant wind gusts over the island, except in the ex- Atmosphere 2021, 12, 827 treme west and east of the island where a punctual maximum above 20 m/s was simulated16 of 22 inside the low-level western jet (Figure 17e,f). Figure 17 shows that the airflow affecting the island at lower troposphere varies between north-easterly and almost easterly along the period. In this case, Figure 11c shows that the downward motion created by orography was10 August,more intense there than were the no upward records motion of significant simulated wind in guststhe top over of the island island, which except ex- in tendsthe extreme up to the west lowlands and east of ofthe the south-eastern island where region. a punctual maximum above 20 m/s was simulatedThe same inside behaviour the low-level was shown western by jet [63] (Figure using 17 AROMEe,f). Figure (Application 17 shows thatof Research the airflow to Operationsaffecting the at islandMesoscale) at lower model troposphere forecasts variesfor the between same day north-easterly at Madeira Island. and almost The authors easterly arguedalong thethat period. the strong In thisdownward case, Figure winds 11 inc showsthe layer that below the downward4 km were caused motion by created the ver- by ticallyorography propagating was more mountain intense wave, than the which upward may motionbe classified simulated as moderate in the top by ofthe the Interna- island which extends up to the lowlands of the south-eastern region. tional Civil Aviation Organization (ICAO) guidelines.

Figure 17. As Figure 8, but for Period 3. Figure 17. As Figure8, but for Period 3.

OnThe 08 same August, behaviour temperatures was shown above by34 °C [63 were] using simulated AROME near (Application the surface ofin Researchthe low- landsto Operations on the southern at Mesoscale) slopes (Figure model 18a), forecasts and forstill the above same 32 day°C during at Madeira the night Island. (Figure The 18b).authors In the argued following that the day, strong there downward was an intensification winds in the of layer this belowhot condition 4 km were (Figure caused 18c). by Onthe 10 vertically August, propagatingthe simulated mountain temperatures wave, were which lower may than be classifiedin the previous as moderate days, around by the 30International °C on the southern Civil Aviation slopes Organizationduring the afternoon (ICAO) and guidelines. below 25 °C in the early night (not shown).On The 08 August,simulated temperatures air temperature above is clos 34 ◦eC to were the observed simulated ones, near except the surface at midnight, in the whenlowlands the model on the tends southern to overestimate slopes (Figure the temperature 18a), and still at the above south 32 coast.◦C during the night (FigureRelative 18b). humidity In the following below 30% day, on the there southern was an slopes intensification was simulated of this in the hot afternoon condition of(Figure 08 August, 18c). with On 10 minimums August, thebelow simulated 20% (Fig temperaturesure 19a). The weredecrease lower in humidity than in the at night previ- wasous intensified days, around by 30 the◦C model on the with southern values slopes belo duringw 15% the in afternoonthe southern and half below of 25the◦ Cisland, in the Atmosphere 2021, 12, x FOR PEER REVIEW 18 of 23 whichearly nightis not (notshown shown). by observations The simulated (Figure air temperature 19b). There was is close a slight to the increase observed in ones,the relative except humidityat midnight, throughout when the the model day, tendsbut not to exceeding overestimate 25% the in temperaturethe southern at slopes the south (Figure coast. 19c). At this moment, the model well represented the spatial distribution of the relative humid- ity over the island. The increase in the relative humidity values over the island gradually occurred along the rest of the period, with the minimums still simulated along the central part of the island (Figure 19d).

FigureFigure 18. 18. AsAs Figure Figure 99,, but for Period 3.3.

Figure 19. As Figure 10, but for Period 3.

4. Summary and Conclusions A set of numerical simulations have been used to explore the atmospheric conditions during three periods of large fire events in Madeira Island. The summer season, charac- terized by low precipitation over the island [35], is a critical fire weather period, and the atmospheric conditions jointly with the complex local terrain are the main factors increas- ing the fire danger and probably influencing the fuel availability, namely in the southern slopes. Concerning the synoptic situation, the Azores Anticyclone was the typical synoptic system over the North Atlantic Ocean inducing the north-easterly airflow towards the island in its coastal zones (eastern side). As it remains almost stationary, the fair weather was maintained over the region for several days. The simulations showed that the atmospheric conditions in the southern slopes are driven by the local orography, which intensified the effects of typical anticyclone condi- tions prevailing over the North Atlantic Ocean. Under a north-easterly flow at lower lev- els, the island shape and orientation may produce a mountain blocking and orographic lifting or flow deflection effects depending on the wind vertical profile [38]. However, the orographic lifting mechanism was not predominant in this study and the relatively weak winds at lower levels were deviated as they approached the island. In general, the winds slow down in the northern region over the ocean and between the ocean surface and the top of the island. Such a configuration, in which the air is forced to flow over the top of the island and around at the lowest atmospheric levels, is consistent with the conceptual

Atmosphere 2021, 12, 827 17 of 22 Atmosphere 2021, 12, x FOR PEER REVIEW 18 of 23

Relative humidity below 30% on the southern slopes was simulated in the afternoon of 08 August, with minimums below 20% (Figure 19a). The decrease in humidity at night was intensified by the model with values below 15% in the southern half of the island, which is not shown by observations (Figure 19b). There was a slight increase in the relative humidity throughout the day, but not exceeding 25% in the southern slopes (Figure 19c). At this moment, the model well represented the spatial distribution of the relative humidity over the island. The increase in the relative humidity values over the island gradually occurred along the rest of the period, with the minimums still simulated along the central Figurepart 18. of As the Figure island 9, but (Figure for Period 19d). 3.

FigureFigure 19. As 19. FigureAs Figure 10, bu 10t, for but Period for Period 3. 3. 4. Summary and Conclusions 4. Summary and Conclusions A set of numerical simulations have been used to explore the atmospheric condi- A set of numerical simulations have been used to explore the atmospheric conditions tions during three periods of large fire events in Madeira Island. The summer season, during three periods of large fire events in Madeira Island. The summer season, charac- characterized by low precipitation over the island [35], is a critical fire weather period, terized by low precipitation over the island [35], is a critical fire weather period, and the and the atmospheric conditions jointly with the complex local terrain are the main factors atmospheric conditions jointly with the complex local terrain are the main factors increas- increasing the fire danger and probably influencing the fuel availability, namely in the ing the fire danger and probably influencing the fuel availability, namely in the southern southern slopes. slopes. Concerning the synoptic situation, the Azores Anticyclone was the typical synoptic systemConcerning over thethe Northsynoptic Atlantic situation, Ocean the inducingAzores Anticyclone the north-easterly was the airflowtypical towardssynoptic the systemisland over in itsthe coastal North zonesAtlantic (eastern Ocean side). induci Asng it remainsthe north-easterly almost stationary, airflow thetowards fair weather the islandwas in maintained its coastal zones over the (eastern region side). for several As it remains days. almost stationary, the fair weather was maintainedThe simulations over the showedregion for that several the atmospheric days. conditions in the southern slopes are drivenThe simulations by the local showed orography, that which the atmospheri intensifiedc the conditions effects of in typical the southern anticyclone slopes conditions are drivenprevailing by the local over theorography, North Atlantic which Ocean.intensified Under the aeffects north-easterly of typical flow anticyclone at lower levels,condi- the tionsisland prevailing shape over and orientationthe North Atlantic may produce Ocean. a Under mountain a north-easterly blocking and flow orographic at lower lifting lev- or els, flowthe island deflection shape effects and dependingorientation on may the pr windoduce vertical a mountain profile [38blocking]. However, and orographic the orographic liftinglifting or flow mechanism deflection was effects not predominantdepending on inthe this wind study vertical and profile the relatively [38]. However, weak winds the at orographiclower levels lifting were mechanism deviated was as they not approached predominant the in island. this study In general, and the the relatively winds slow weak down windsin theat lower northern levels region were overdeviated the ocean as they and approached between the the oceanisland. surface In general, and thethe topwinds of the slowisland. down Suchin the a northern configuration, region in over which the theocean air and is forced between to flow the overocean the surface top of and the the island top andof the around island. at Such the lowesta configuration, atmospheric in which levels, the is consistentair is forced with to flow the conceptualover the top models of the island and around at the lowest atmospheric levels, is consistent with the conceptual

Atmosphere 2021, 12, 827 18 of 22

of stably stratified flows crossing three-dimensional obstacles presented by [64] and for situations of slightly faster winds or weaker stability [65]. In the third episode, our results showed an intense downward motion reaching the Madeira foothills in the southern slopes and eastern part of the island. Such a situation indicates that the downslope motion can be associated with a mechanically driven mechanism. Such a mechanism involves the upstream blocking of low-level flow by a mountain barrier, with drier air flowing down to replace it in the lee of the mountains [66]. In addition, as the drier air from above descends the lee slopes it is warmed by adiabatic compression. Over the island, the downward motion created by the local orography at the southern slopes was evident from the simulations, which was represented through the wind gusts field at 10 m. The intense wind gusts at the surface in the southern slopes, namely in the highlands, was observed in all periods, and mainly during the night-time (corresponding to the maximum fire daily expansion showed in Table1). In the first two episodes, the downward motion was restricted to the highlands up to the southern half-slope, while closer to the coast the wind blew from the sea, countering the fire spread to lower altitudes. The combined effect of terrain and atmospheric conditions increased fire danger by leading the maximum temperatures above 35 ◦C and relative humidity around 15%, exacerbated by intense gusts, in particular in the third episode. In this last episode, the first day was characterised by extreme gusts in the southern slopes not thwarted by the sea breeze, produced by the intense north-easterly winds that affected the top of the island. This situation favoured a high temperature during the afternoon, as well as overnight temperatures above 30 ◦C. The warm night probably influenced the fuel moisture, as the relative humidity dropped from levels below 25% in the afternoon to below 15% along the night. The model also showed the generation of local downslope winds, which contribute to intensify fire danger, increasing air temperature, reducing the relative humidity and driving the fire spread. In general, the model represented well the temperature and relative humidity at surface, despite some local over- or underestimation. The evolution of the fires was driven from a combination of factors that led to an enhanced fire danger by also favouring fuel availability. The north-easterly winds are drier due to the orographic effects, and the warm flow gradually decreased fuel moisture. Such environment is a strong indicator of potentially extreme fire behaviour. In addition, the strong wind gusts and the rugged terrain challenges fire suppression, allowing fire to expand over large areas in short time periods. The high-resolution simulations showed fire-prone areas over the island and weather patterns related to high daytime temperatures and sometimes overnight, low humidity, and strong wind gusts that favour fire growth. The absence of precipitation is another factor contributing for this propitious condition to fires over the island. It is noteworthy that sometimes the highest fire danger, based on these elementary meteorological variables, was identified near urban areas in the southern foothills, namely in Funchal city, where one of the August 2016 extreme fire events took place. All of these large fire events analysed in our study showed very high rates of expansion over short periods of time, which, cumulatively with the topographic roughness, challenged the suppression capacity installed on the island and threatened a high number of natural and man-made values. Forest fires are becoming more and more common and destructive, with several factors affecting their behaviour. Identifying fire weather conditions exacerbated by local effects at the surface may be useful for specific regions, mainly for the inhabitants of forested islands, where fire danger can be directly linked to these factors. The study shows an alternative that can identify fire danger and anticipate fire behaviour in Madeira Island. However, the study highlighted just two of the three basic parameters associated with fire behaviour, i.e., the meteorological aspects and terrain effects enhancing fire danger. Therefore, an analysis also including the spatial distribution of fuel types and structure must be conducted in the future, as well as studies addressing the fire danger during the fire season. Additionally, the interactions between fire and atmospheric circulations must also be taken into account. Atmosphere 2021, 12, 827 19 of 22

In summary, the results found in our study may support strategies for reducing the risk posed by the fire danger created by meteorological and terrain aspects. The use of high-resolution simulations is able to indicate the regions more proneness to large fires, namely those affected by the highest near surface temperatures and lowest values of relative humidity. It is suggested for future works the consideration of vegetation characteristics to develop well-suited strategies to prevent the occurrence of large fires and to well suppress fires in these conditions, i.e., through local systems able to compute scenarios of fire growth under a fire forecast context. Such a framework could support the development of better fire management practices, as well as promoting a sustainable development.

Supplementary Materials: The following are available online at https://www.mdpi.com/article/ 10.3390/atmos12070827/s1, Figure S1: Vertical profile of horizontal wind velocity simulated at 500 m resolution and wind direction: (a) 1500 UTC—18th July 2012, (b) 1400 UTC—19th July 2012. Author Contributions: Conceptualization, F.T.C. and R.S.; methodology, F.T.C. and R.S.; software, F.T.C. and R.S.; formal analysis, F.T.C. and R.S.; investigation, F.T.C.; resources, R.S., N.G.; data curation, F.T.C., N.G.; writing—original draft preparation, F.T.C.; writing—review and editing, R.S., N.G.; visualization, F.T.C., N.G.; supervision, R.S.; project administration, R.S.; funding acquisition, R.S. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the European Union through the European Regional Devel opment Fund in the framework of the Interreg V A Spain-Portugal program (POCTEP) through the CILIFO project (Ref.: 0753_CILIFO_5_E), and also by national funds through FCT—Foundation for Science and Technology, I.P. under the PyroC.pt project (Refs. PCIF/MPG/0175/2019) and ICT project (Refs. UIDB/04683/2020 and UIDP/04683/2020). Informed Consent Statement: Not applicable. Acknowledgments: We want to thank Paulo Fernandes (University of Trás-os-Montes e Alto Douro; Collaborative Laboratory ForestWISE; Independent Technical Observatory for Rural Fires) for making available the annual burned areas on Madeira Island and for the spatial distribution of the burned areas. The authors are grateful to the Portuguese meteorological service (IPMA), for providing meteorological data and to the European Centre for Medium-Range Weather Forecasts (ECMWF), for the provided meteorological analysis. Conflicts of Interest: The authors declare no conflict of interest.

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