Investigation of synoptic patterns of fire occurrence in the forests of the western Alborz Mountains

Forest fire is considered as a natural disaster and major potential threat in many parts of the world. Due to the lack of a comprehensive study in terms of the synoptic conditions of the fire incident in the studied area, the present study was conducted in order to identify the predominant synoptic patterns of fire occurrence in the western Alborz Mountains. To this end, first, the days of fire were obtained from the Department of Natural Resources of Gilan Province and the product (MCD14) Modis sensor (2007–2020). In order to determine atmospheric synoptic patterns, atmospheric maps were obtained from the NCEP site on all fire days. Totally, 240 fires occurred. Among the months of the year, July, August, and December had the highest incidence of fires. Based on the fires that occurred, three predominant synoptic patterns had the highest frequency of fires, including (1) Saudi-African high pressure dominant in the hot and cold seasons of the year, with three forms of omega blocking (16.5%), ridge (24.8%), and intrusion (22.2%), in total with a frequency of 63.5%; (2) European Migrant high-pressure system intrusion dominant in the hot period of the year, with a frequency of 21.7%; and (3) subpolar low pressure, which is generally dominant during the cold period of the year and responsible for about 14.8% of the fires in the region. Therefore, the most common occurrence of natural fires in the region is due to the high-pressure influence of Arabia and Africa in the hot and cold periods of the year.


Introduction
Mountain systems play an important role in their surrounding changes.The different components of the mountains modify and increase the intensity of atmospheric elements as well as phenomena.Mountain systems play an essential role in the formation of atmospheric phenomena such as katabatic (mountain to plain), anabatic (plain to mountain), and Foehn (warm and dry) winds.Forest fire with natural and human origin is considered as one of the most important threats to forests in northern Iran.Meanwhile, climatic factors are also very influential in the occurrence and spread of fires (Hajj et al. 2017).The importance of atmospheric conditions is not only as a single factor for causing fire, but also it can be stated that the influence of other factors of fire, such as human factors, is itself a function of atmospheric factors.If atmospheric conditions are undesired, fire cannot spread (Farajzadeh et al. 2015).
The increase in the occurrence of frequent fires in the forests of northern Iran in recent years has caused a great deal of damage and loss to the environment, forests, villages, and their inhabitants on a large scale.The compaction of forests in northern Iran, their concentration and interference in the daily life of inhabitants, the accuracy in the statistics of past fires, and the damage caused by them show the importance of this issue and provide the necessary solutions (Mohammadzadeh andFallahi, 2007: 2, quoted by Eskandari 2015).Thus, it is necessary to prevent and deal with this crisis.In order to minimize the damage to the forest due to fire, it is necessary to have complete knowledge of the process of past fires, and after fully understanding the temporal and spatial processes, it is necessary to spatially analyze the occurrence of fires in each region to design protective strategies (Ishaqi and Shatai Joybari, 2016).
Given the importance of forest fires, various studies have been conducted in this field in the forest regions of Iran and the world.Keeley (2004) investigated the role of climatic factors and southern fluctuation index in the California coastal fire regime and stated that in autumn fires, Foehn wind plays a key role.A study by Beverly and Martell (2005) found that in Canada, wildfires were far more widespread in the western part of the Bural Forests than in the east due to the severe droughts that dominated the region.Pereira and Trigo (2005) studied the temporal and spatial distribution of fire features (between 1980 and 2000) using comprehensive Portuguese forest fire data.The results revealed that meteorological conditions play a key role in both combustion and fire spread.Reinhard et al. (2005) attributed the increase in fires in southern Switzerland to rising temperatures and declining humidity in response to climate change.
A study by Hayasaka et al. (2006) on the rate of increase in Alaska forest fires in relation to climatic factors such as lightning, Foehn wind, and droughts found a difference between an increase in fires and elevation in temperature each year.In 2004 and 2005, a correlation was found between drought in August and the occurrence of Foehn wind.Hawbaker et al. (2008) in the USA investigated the percentage of fires detected using MODIS sensor images.Using Terra and Aqua images simultaneously, they were able to identify 82% of the fires studied.A study by Morgan et al. (2008) found that wildfires in the North Rocky Mountains occurred in the twentieth century during the years with hot spring and dry and less rainy summer.
According to a study by Sharples et al. (2010) in the Australian Alps in southeastern Australia, Foehn wind caused sudden changes in climate variables and increased the risk of fire.A study by Slocum et al. (2010) found that wildfires in Florida are often controlled by rapid changes in seasonal precipitation.Wastl et al. (2012) found that in recent years, the effect of rising temperatures and changing rainfall patterns on the likelihood of fires in different parts of the Alps has been variable.Pollina et al. (2013) explored synoptic patterns of fires in the northern USA and concluded that Appalachian high pressure in the center and south winds combined with thermal low pressure played an important role in forest fires in North America.
In a study on the role of climate systems in controlling the magnitude and severity of wildfires in the Mediterranean region, Hernandez et al. (2015) showed that at the time of wildfires at the middle atmospheric level, blocking played a major role in the temporal and spatial spread of fires.Duane et al. (2016) introduced the MedSpreadda model to test fire performance.Using this model, they studied fires affected by convection, topography, and wind.They found that for each of the three patterns of fire spread, some factors have a greater impact on fire simulation than others, and studies indicate a strong relationship between climate information, fire spread, and simulation of fire states.
Elsewhere, Hayasaka et al. (2016) evaluated Alaska wildfires to investigate climate conditions on a synoptic scale.The results showed that following wildfires, climatic conditions typically lead to two peaks of the center, before and after the movement of high-pressure systems from south to north across Alaska.Duane and Brotons (2018) analyzed fire spread spatially.They found that classifying the prevailing climatic conditions on large continental scales is a good alternative to integrating climate-related factors and fire state features on a regional scale.Hayasaka et al. (2019) inspected climate conditions for wildfires in the northern forests.The results showed that the fire was very active in all periods since hot air masses approached the four study areas from the south.These movements of hot air masses are mainly related to the circulation of westerly winds and mean, while strong winds occur when hot and dry air masses approached the area.Tariq et al. (2021a), on spatio-temporal analysis of forest fire events in the Margalla Hills, consider both environmental factors (altitude, precipitation, forest type, terrain, and humidity index) and socioeconomic (population density, distance from roads and urban areas).The results showed that the fires were mainly distributed in urban areas and their probability of occurrence was related to accessibility and human behavior/activity.Tariq et al. (2021b) analyzed spatial patterns of danger of forest fire at Margalla Hills.They did this using data on burnt areas using Landsat data to classify forest fire severity with different parameters (climatic, vegetation, topography, and human activities).The results showed that the burned areas have increased at a rate of 25.848 ha/day (R 2 = 0.98) if the number of total days since the start of the fire has increased.As a result, forest density, distance to roads, average quarterly maximum temperature, and average quarterly mean wind speed were highly correlated with the fire severity.Tariq et al. (2021c), on quantitative analysis of forest fires in Southeastern Australia using SAR data, reached this conclusion.The VV polarization shows some potential to detect burned areas under wet conditions.

The study area
The natural geography of the studied area is influenced by two major factors: the Caspian Sea as the largest lake in the world and the Alborz mountain range, which is part of the Alpine-Himalayan orogenic belt.Each of these geographical factors alone can affect the climate of the region and create its own landscape.Figure 1 depicts the location (48 to 50° east longitude and 36 to 38° north latitude) of the study area.

Materials and methods
In this study, in order to investigate the synoptic patterns leading to a fire in the western Alborz Mountains, first, the days of fire were obtained from the Department of Natural Resources of Gilan Province and the product (MCD14) Modis sensor (2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018)(2019)(2020).The longitude and latitude of the affected regions were added to GIS, and the fire spatial database was prepared during the statistical period (Fig. 1).In order to determine atmospheric synoptic patterns, atmospheric maps were obtained from the NCEP/NCAR site on all days of the fire with a spatial resolution of 2.5 * 2.5 degrees (Kemp et al. 2012).These data include air temperature at 850 hPa; this level is about 1500 m above the ground, and many authors (Duane and Brotons 2018;Cardil et al. 2014;Ruffault et al. 2017) have emphasized the importance of this level in the spread of fire.The sea level pressure map shows the low-and high-pressure regions on the ground surface.The degree of stability and instability of the atmosphere at this level affects the spread of fire, the intensity of fire, and the movement of smoke (Haines 1988;Potter 1996;Potter and Anaya 2015;Tatli and Türkeş 2014).The meridian (v) and orbital (u) winds at 500 hPa, 755 hPa, 850 hPa, and 925 hPa show flow maps used to indicate wind flow at different levels.The wind is the main stimulus for the spread of fire (Rothermel 1983).Specifically, 925 hPa was selected as the representative of the troposphere (the layer closest to the ground surface).The geopotential levels of 850 hPa and 925 hPa are used to investigate the synoptic patterns that lead to ridge as well as cyclone and anticyclone intrusion and expansion (Keikhosravi 2019;Keikhosravi 2021), where geopotential levels of 500 hPa and 700 hPa are used to select omega blocking systems (Wiedenmann et al. 2002).Figure 1 displays the location of fires that occurred over the 14-year period.The flowchart of Fig. 2 shows all the research steps.

Results
According to Table 1, a total of 240 fires occurred during the statistical period whose data were recorded.The year 2010 had the highest frequency of fires (42 days), and 2013 had the lowest frequency of fires (9 days).Among the months of the year, July, August, and December had the highest frequency of occurrence of fires, respectively (38 days, 37 days, and 24 days, respectively).
In order to extract the synoptic patterns of fires in the southwestern Caspian Sea, after investigating the ground surface pressure and the synoptic conditions of the upper levels of the atmosphere on the days of the fire, three synoptic patterns that had the highest frequency were extracted.According to Table 2, the highest occurrence of fires (24.8 and 22.2) has been related to ridge synoptic patterns and the expansion of Saudi-African high-pressure intrusion.

Synoptic patterns of Saudi-African high pressure
At high atmospheric levels, Saudi Arabia-Africa high pressure (Lashkari et al. 2017) is the most important climate control system in Iran.This system covers different levels of the year from sea level to high atmospheric levels.The main feature of this high-pressure system in Iran is that it intensifies the heat of the surface layer through the heating resulting from the adiabatic phenomenon in the region.This system leads to fire in three ways in the study area (Fig. 3).
(A) Saudi-African high-pressure blocking: it is a highpressure system extending from the ground surface to the upper atmosphere, which is commonly known as highpressure blocking or omega (Ω).The low-pressure system is drawn to the north and/or slowed in the trough located in   the west and east.The omega blocking system often stays in place for days or weeks (Omidvar 2010).For the blocking phenomenon, most researchers agree on the low-pressure instability of the planetary scale (Austin 1980;Hartmann and Ghan 1980;Namias 1950).The causes of instability are mainly temperature anomaly in the oceans and large seas, land-sea temperature difference, temperature difference in the ground different parts along the orbit, temperature difference in the sea levels along the orbit, and the effect of altitude (Azizi 1999).According to Table 2, 12.4% of fires in the study area have been related to omega synoptic pattern.Also, the frequency of occurrence in hot seasons (spring and summer) has been 64% and 36% in cold seasons (autumn and winter).In the cold seasons of the year, subpolar low pressure at the lower troposphere levels and the intrusion of Saudi high-pressure omega at 500 hPa and 700 hPa; and in the hot seasons, Pakistan and Central Iran low pressure at 850 hPa plus the intrusion of Saudi high-pressure omega led to fires in the region.(B) Saudi-African high-pressure ridge: as atmospheric upper-level winds move from west to east like a string, they take on a north-wavy pattern.In this wave pattern, sinking is trough and the bulge is called ridge.In the waveform pattern, the waves facing north are called trough while the waves facing south are called ridge.In the northern hemisphere, the flow inside the ridge is clockwise and the ridge line indicates The ground surface high-pressure systems are formed under high-level ridge.In the northern hemisphere, the clockwise motion of high-level ridge amplifies the clockwise motion of surface high pressure.When a surface high pressure is formed under a high-level ridge, the air moves at surface high pressure at a rate between one-third and one-half of the wind speed of the high level.In the event of a fire, this pattern causes the flames to spread by wind to the surrounding regions.In this synoptic pattern, the occurrence of fire in the region is about 24.8%.This synoptic pattern often occurs in the cold months of the year in two ways: (1) In the first pattern from the surface to the level of 850 hPa, Siberian high pressure is dominant, and at 500 hPa and 700 hPa, Saudi Arabia-Africa high-pressure ridge penetrates into the region; (2) in the second pattern, Siberian and European migrant high pressure would merge at 850 hPa, and at 500 and 700 hPa, Saudi-African high-pressure ridge dominates the study area.These two patterns often provide the conditions for Foehn wind (Keikhosravi et al. 2020a(Keikhosravi et al. , 2020b)).
Foehn wind is the dry and hot air that occurs under special conditions on the slopes behind the mountain wind.When air masses hit a mountain and are forced to ascend, this will be adiabatic (the adiabatic process is the process in which a hypothetical air package ascends or descends without interacting with the surrounding air) once the humid air ascends and cools, latent heat released accelerates the process of ascending the mountain and reaching the top of the mountain.Here, some humidity is released by rain or snow.
Thus, when this air mass descends from the other side of the mountain, due to low humidity and compaction, it heats up earlier in the hot seasons, when Pakistan low pressure spreads to the level of 850 hPa and the intrusion of Saudi-African in the upper troposphere (500 and 700 hPa) provide the ground for fire.
(C) Saudi-African high-pressure intrusion: the percentage of fires in this pattern in the region is 22.2%.However, its frequency is higher in cold seasons (66%) than in hot seasons (34%).In this pattern, in the hot and cold seasons of the year, the expansion of Siberian high pressure and Pakistan low pressure to the level of 850 hPa and the intrusion of Saudi-African high pressure at the levels of 500 hPa and 700 hPa, respectively, provide the ground for fires in the region.This synoptic pattern also provides the conditions for Foehn wind in the cold seasons of the year.

Ridge synoptic pattern (study sample March 9, 2009)
In this synoptic pattern, Saudi-African high-pressure ridge intrusion has caused the fire (Fig. 3b). Figure 4a displays the sea level synoptic conditions on March 9, 2009.On this day, at the time of the fire occurrence, a low-pressure system with an isothermal curve of 1000 hPa at 55° northern latitude and 20° eastern longitude was closed, and a co-pressure system of 1010 hPa also covers the southwestern Caspian Sea plus its shores.Concurrent with these conditions, the high-pressure center with the co-pressure curve of 1034 hPa entered Iran from the northeast as well as east and covered the center and south, Zagros, and northwestern heights of Iran.As shown, the Siberian high-pressure system entered Iran from the east-west along the eastern border and then spread to the southern slopes of Alborz.The pressure created in northwestern Iran and on both sides of the western Alborz heights between the two cyclone systems of the Caspian Sea as well as the Siberian anticyclone system leads to a strong wind with a speed of more than 20 knots on both sides of the western Alborz heights.
The dominant synoptic pattern at 925 hPa is very similar to that of the sea level, as indicated in Fig. 4b, due to hot advection through the southern flows of the western slope, cyclone to the west coast of the Caspian Sea, tropical cyclone due to subpolar cold advection through the northern flows and due to an increase in temperature, anticyclone on the Caspian Sea causing the hot air advection of the southern latitudes to the western Alborz so that the mean temperature of this day at the level reaches more than 290 degrees Kelvin.This pattern follows up to 850 hPa (approximate boundary of the boundary layer).Figure 5a reveals a flow pattern of 700 hPa.At 700 hPa, the Siberian cyclone has disappeared, and instead, the deep ridge covers Iran.Due to the predominance of hot and humid southern flows, meridian flows, and proper injection, the eastern Mediterranean trough has been completely strengthened, and as shown, this trough has expanded to a width of 20 degrees (northern Sudan).This trough southward expansion and suitable temperature advection from the southern latitudes in the border layer through the trough forward flows provide very suitable conditions for instability in northwestern Iran and the windward slopes of the western Alborz.
The thermal and compressive pattern resulting from the dominance of the south flows has caused the wind speed in front of the trough to exceed 30 knots.At 500 hPa (Fig. 5b), trough and ridge are in very good agreement with the lowerlevel trough and ridge.The flows in the middle layer provided very good conditions for strengthening the instability in the front of the trough and the subsidence of hot air in the ridge.Saudi high pressure with east-south movement is located on the hot seas of Oman and the Indian Ocean, causing the air to settle and subside on the surface of the seas; also, with its clockwise rotation, it has caused the transfer of humidity to the front of the trough.The flows in front of the trough and the region are completely southwestern, and with the strengthening of the meridional and vortex flows, the resulting instability on the heights would increase.Thus, at this level, the advection flow from the southern latitudes is associated with hot advection on the region.
Due to the dynamic conditions in northwestern Iran, appropriate humidity advection and the release of non-adiabatic heat from the condensate increased the air temperature in the region, especially in the slope back to the wind, and intensified the condition of Foehn as well as subsequent fires in the region.Keikhosravi et al. (2020a), in investigations on the synoptic maps of 35 Foehn events in the Western Alborz mountain range, reported that three groups of anticyclone or high-pressure centers were affected by the synoptic pattern of the region in the days involved.The first group is the Siberian high-pressure tabs, the second group is the anticyclone of Saudi Arabia, and the third group is a combination of African anticyclones, European immigrant high-pressure tongue, and Siberian high pressure.
Synoptic patterns leading to the intrusion of the European immigrant high pressure (study sample: August 14, 2010) This synoptic pattern occurs only in the hot seasons of the year and leads to fires.At the lower troposphere levels (sea level up to 850 hPa), the migrant high pressure dominates the region, and at 700 hPa and 500 hPa, the expansion of the Saudi-African high-pressure system causes subsidence and stable air and finally provides the necessary conditions for fire in the region.Specifically, 21.7% of fires in the region occur due to the formation of this synoptic pattern (Fig. 6).
Figures 6 and 7 display synoptic conditions of August 14, 2010, as an example of a pattern of European migrant highpressure system intrusion, in which a high-pressure thermal center is at sea level with a central core of 1028.3 hPa at latitudes of 60-65 ° N and longitudes of 50-55 ° E (Fig. 7a).This high-pressure system in the southeastern direction covered the western and northwestern Alborz in the country.In contrast, a low-pressure thermal center with a central pressure of 999 hPa has been formed on the deserts of Saudi Arabia and Pakistan, with this low-pressure center system covering most of the country except the northwest of the country.The pressure difference between the migrant high pressure and Pakistan-Saudi Arabia low pressure has caused strong winds in the southwestern slopes of Alborz Mountain, so the wind speed is more than 10 knots in the northeastsouthwest direction from the Caspian coast to Central Iran.At 925 hPa (Fig. 7b), the ground surface conditions are also such that the core of the cyclone migrant center is displaced westward to its original position (45° east longitude) and lower latitudes.Saudi cyclone with a central core of 705 geopotential meters with good clockwise rotation causes the hot air of the southern latitudes to move forward and the Fig. 6 Location of fires occurred in the patterns leading to the intrusion of the European immigrant high pressure migrant cyclone so that in the western Alborz, the day mean temperature has reached more than 300 degrees Kelvin.The air is very slow and tends to inertia.This relative inertia of the air in this layer has increased the heat intensification in the lower layer.This pattern governs the entire lower layer of the troposphere at 850 hPa (Fig. 8a).
The synoptic conditions of 700 hPa level do not change to the lower levels (Fig. 8b), such that the anticyclone migrant system shifts to the west and moves parallel to the eastern longitude of 30° and northern latitude of 54°, with this high-pressure system covering only the northern half of the Caspian Sea.In contrast, cyclone Saudi Arabia with a central core of geopotential level of 3195 m covers most of Iran and the study area.As shown, the wind speed in the middle layers is very low and almost calm, as well as motionless.This vertical arrangement indicates the stability of the atmosphere in the middle layer.These synoptic conditions have increased the heat of the layer and the lower levels of the atmosphere.At the level of 500 hPa, the same conditions are observed.Thus, the heat transduced from the lower layer and stability and subsidence of the air in the middle layer of the atmosphere caused a strong heat wave on the western Alborz, plus an unexpected rise in temperature.

Subpolar trough (study sample:
November 21, 2009) This synoptic pattern occurs only in the cold seasons of the year, such that the subpolar low-pressure side is formed at 50-55° northern latitude and trough is located on the Caspian Sea.In this synoptic pattern at sea level based on fire samples, Pakistan-Saudi low-pressure and high-pressure migrant prevail, while at high levels (500 hPa, 700 hPa, and 850 hPa), subpolar low-pressure trough dominates the region.The frequency of this pattern during the statistical period is about 14.8% (Fig. 9). Figure 10  entire area, the lower and middle layers of the troposphere are in the west of the western and northwest Caspian.These flows lose their humidity in dealing with the mountainous obstacles of the western sea (from the heights of Talesh and western Alborz) through the erographic flows prevailing in the windward slopes.The non-adiabatic heat released by the wind into the subsidence stream on the lee slopes as well as the heating resulting from the dynamic descent of the air has created the Foehn phenomenon on the lee slopes.The subsidence flow on the slope of the lee has dried up due to the heating created and provided the necessary conditions for intensifying fires in the forests of the west as well as southwest of the Caspian Sea. Figure 10 shows this synoptic pattern at the lower and middle levels of the troposphere.At 925 hPa (Fig. 10b), subpolar low pressure with a central pressure of 690 hPa is formed at 55° northern latitude and 60° eastern longitude, with this trough covering the entire territory of Iran.In contrast, the anticyclone migrant center with a central core of 950 geopotential height is formed at 40° northern latitude and 20° eastern longitude, covering the western part of Iran.The confrontation of these two systems in the northwest of the country has caused the flows in the southwest Caspian Sea and the windward slopes of western Talesh, with the extension of the wind being perpendicular to the slope.The same synoptic conditions are present at 500 hPa, 700 hPa, and 850 hPa.Keikhosravi et al. (2020b), in investigating the Foehn phenomenon in the Western Alborz mountain range and its effect on the amount of thermal stress on vegetation, concluded that Foehn is a common phenomenon in the eastern and northern slopes of the Western Alborz in Iran.
The frequency of Foehn in the cold period of the year grows significantly compared to the warm period of the year.Based on the study sample of September 4, 2015, the influence of the Foehn phenomenon in these areas has increased the radiation received between 600 and 700 W/m 2 .

Constraints and limitations
In this study, two databases were used to investigate the frequency of fire occurrence days in the southwestern region of the Caspian Sea.
The use of the fire product (MCD14) of Modis sensor in the time interval from 2007 to 2020.
Database of the Natural Resources Department: Unfortunately, in some years, the natural resources department of Gilan province did not record fire incidents.
Certainly, if the incidents of fire were recorded by the General Department of Natural Resources of Gilan province during the entire statistical period, the frequency of fire incidents would be more accurate.However, to better investigate the research topic, the fire product (MCD14) of the Modis sensor was used.

Conclusion
In the western Alborz Mountains, the homogeneity of fuels, climatic conditions, and topography throughout the region affect the occurrence and spread of fires.A total of 240 fires occurred during the study period of 2007-2020.Totally, 64% of fires occurred during the cold period of the year and 36% of fires occurred during the hot period of the year.
In order to extract the synoptic patterns of fire, after investigating the surface pressure and synoptic conditions of the upper levels of the atmosphere on the days of the fire, 3 synoptic patterns with the highest frequency were extracted.(A) Synoptic pattern leading to Saudi Arabia and Africa: from high sea level to high atmospheric level.The main feature of this high-pressure system is that it intensifies the heat of the surface layer through heating the adiabatic phenomenon in the region.This system leads to fire in three ways in the study area: (1) Saudi-African high-pressure blocking, with 16.5% of fire occurrences in the study area being related to the omega synoptic pattern.Also, the frequency of occurrence in hot seasons (spring and summer) was 64% and 36% in cold seasons (autumn and winter); (2) Saudi Arabia-Africa high-pressure ridge, in this synoptic pattern, the occurrence of Syrian fire in the region is about 24.8%; (3) intrusion of Saudi-African high pressure, the percentage of fires in this pattern in the region is 22.2%.However, its frequency is higher in cold seasons (66%) than in hot seasons (34%).(B) Synoptic pattern leading to the intrusion of European migrant high pressure: this synoptic pattern occurs only in the hot seasons of the year and leads to fires.At the lower troposphere levels (sea level up to 850 hPa), migrant high pressure dominates the region; at 500 hPa and 700 hPa, the expansion of Saudi-African high pressure causes subsidence and stable air and finally provides the necessary conditions for fire in the region.Specifically, 21.7% of fires in the region occur due to the formation of this synoptic pattern.(c) Subpolar low-pressure trough occurs only in cold seasons of the year.So, subpolar low pressure is formed at 50° and 55° north latitude, and trough is located in the Caspian Sea.In this synoptic pattern at sea level, Pakistan-Saudi low pressure and migrant high pressure prevail, and at high levels (500 hPa, 700 hPa, and 850 hPa), subpolar lowpressure trough dominates the region.The frequency of this pattern during the statistical period has been about 14.8%.The results of this research clearly showed that one of the reasons for the occurrence and spread of fire is the synoptic condition of the region.Therefore, with the rule of such weather conditions, it can be useful for the decision-makers of forest protection and fire control not only in the west of the Alborz mountain range but also in the neighboring countries that face such weather conditions.In future research, it is suggested to model future fire regimes by classifying fire spread patterns according to synoptic weather conditions.

Fig. 1
Fig. 1 Location of fires occurring in the study area during the statistical period of 2007-2020

Fig. 2
Fig. 2 Flowchart of the study framework

Fig. 4
Fig. 4 Synoptic conditions and arrangement of systems at sea level (A) and 925 hPa (B), March 9, 2009

Fig. 7 Fig. 8
Fig. 7 Synoptic conditions and arrangement of systems at sea level (A) and 925 hPa (B), August 14, 2010 Fig. 9 Location of fires occurring in trough synoptic pattern

Fig. 10
Fig. 10 Synoptic conditions and arrangement of systems at sea level (A) and 925 hPa (B), November 21, 2009