Analysis of lightning vulnerability level in the City of Mataram and surrounding area using the simple additive weighting method

. Mataram City, West Lombok and Central Lombok Regencies are areas that have a high level of infrastructure development. This high level of infrastructure development has indirectly increased the risk of lightning strikes in the city of Mataram and its surroundings. This study aims to determine the level of threat, susceptibility, and vulnerability to lightning strikes in the city of Mataram and its surroundings, and to find a correlation between the increase in land use as buildings and settlements with the increase in the number of lightning strikes. The lightning data was obtained from the monitoring results of the Mataram Geophysics Station in the 2017-2021 period which was processed using the Simple Additive Weighting method. From the processing results, the level of vulnerability to lightning in the very high category is in Selaparang and Mataram sub-districts. The results of the Pearson correlation calculation in an increase in the number of areas used as buildings and settlements to an increase in the number of lightning, obtained 14 districts with high Pearson correlation index values and 3 districts with very high Pearson correlation index values which included Batukliang, Sekotong, and Jonggat Districts.


Introduction
Indonesia is a tropical archipelago countery, with the sea covering 60% of the country's land area.High evaporation and the development of clouds, especially the Cumulonimbus (Cb) type, are the results of this.High clouds will produce airborne contact charges that will result in an electric spark that is known as lightning.Indirectly, this circumstance has an impact on Indonesia's average annual number of 200 thunderstorm days [1].
West Nusa Tenggara Province's capital, Mataram, has a highly developed infrastructure.Furthermore, community activities in the fields of business, social life, culture, and tourism are concentrated in the region surrounding the city of Mataram.In addition to Mataram City, West Lombok and Central Lombok Regencies have developed their infrastructure to a considerable degree.Indirectly, the chance of lightning strikes will rise with increased infrastructure development [2].The need for electronic equipment is quite strong in the digital 4.0 era.The demand for electronic equipment will inadvertently raise the danger of lightning-related harm to electronic equipment.Of course, using electronic equipment makes you extremely vulnerable to lightning strikes.This is due to the possibility that lightning strikes may damage electronic devices inadvertently [3].Lightning strikes can not only disrupt the flow of high-voltage electricity, but can also cause fatalities for people who are directly struck by lightning [4].According to koranmerah.com, two farmers were killed when lightning struck three of them  Corresponding author: muhammad.azany.harits@stmkg.ac.id in the city of Mataram.In addition, a fisherman in West Lombok Regency perished due to a lightning strike, according to lombokpost.jawapost.com.Most recently, in March 2023, a farmer in the East Praya neighbourhood of Central Lombok Regency died as a result of a lightning strike (postkotantb.com).Residents who are engaged in outdoor activities are struck by lightning.This demonstrates the high frequent of lightning strikes in the Lombok area.Therefore, additional research is required to analyse the lightning vulnerability in this area.This level of lightning susceptibility depends on a number of lightning, region's population, area width, and number of area used buildings and settlements.
The method used in this study is the Simple Additive Weighting (SAW) method.The concept of this method is basically looking for a weighted sum of performance ratings for each alternative across all attributes [5,6].Many studies have been carried out on determining the level of lightning vulnerability using the SAW method, including Sugiyono and Agani [7] in Lampung Province, Gunawan and Pandiangan [8] in Bali Province, and Umaya and Supadiyono [1] in Surabaya.From this research it is hoped that it will provide knowledge for the community regarding the level of lightning vulnerability in the city of Mataram and its surroundings, as a first step in education and mitigation of lightning disasters and as a reference in urban planning or in planning for the construction of high-rise buildings and Base Transceiver Station (BTS) towers.

Lightning
Pabla [9], explained lightning as a natural phenomenon as result of the release of both positive and negative charges that are stuck in clouds.Due to variances in the speed of light and sound wave propagation, lightning strikes and thunderclaps occur at different times [9].A potential difference between two media-in this case, clouds, the ground, and air-is what triggers the occurrence of lightning.With a current density of 2 x 10(-12), the potential difference between the earth's surface and the ionosphere is normally between 200 and 500 thousand volts.Due to the existence of cumulonimbus clouds, lightning typically happens when it is raining or just about to rain [8].According to the propagation mechanism, there are four different forms of lightning, as follows [9]: Intracloud lightning (IC) occurs because in the same cloud there are different charge centres in it.IC lightning propagates only within the cloud and is seen as scattering of light from within the cloud Cloud-to-cloud (CC) lightning occurs due to different clouds because there is a different charge centres for each cloud.The dispersion of this CC lightning is from one cloud to another.Although this particular sort of lightning does not endanger buildings or life on the surface of the planet, it is recognized to be a threat to aviation.
Cloud-to-air (CA) lightning occurs between clouds and the surrounding air due to differences in charge centres.Clouds have a positive charge center while air has a negative charge center.This particular form of CA lightning spreads from the cloud into the surrounding air.
Cloud-to-ground (CG) lightning occurs between clouds and the ground due to differences in charge centres.This lightning occurs due to the discharge of charges in the lower clouds towards the earth.Because it can harm items above the ground, this kind of lightning is hazardous.

Simple additive weighting
According to Fishburn [6] and MacCrimmon [5], the weighted sum approach, also known as the simple additive weighting method, essentially seeks the weighted sum of the performance ratings for each alternative across all criteria.In order to compare the choice matrix (X) with all currently known alternative ratings, this method necessitates a decision matrix normalisation procedure (X) into a scale.The Simple Additive Weighting completion steps are as follows: 1. Determine the reference criteria in decision making (Ci).2. Determine the decision matrix based on the criteria and determine the suitability rating of each choice on each criterion (Ci).3. Matrix normalisation uses an equation adjusted to the type of attribute to produce a normalised matrix R (cost or benefit).4. Complete the ranking process by combining the normalised matrix multiplication R with the weight vector, choosing the best option (Ai) based on the largest value.
The formula for normalisation is: Where : � �� = normalised work rating of alternative Ai & attribute Cj � �� = value in of i-alternative on the j-attribute ��� � �� =maximum value of j-attribute ��� � �� = minimum value of j-attribute To determine the preference value for each alternative, it is formulated as follows: Where : �� = preference value for each i-attribute � � = weight for each attribute � �� = normalised work rating of alternative Ai & attribute Cj

Pearson correlation
Pearson (1934) introduced a new method to test the compatibility between the theoretical distribution and a number of observed data, which became known as Pearson's product-moment correlation coefficient.The strength, adaptability, and simplicity of the Pearson Correlation technique make it advantageous for testing the fit of any continuous distribution.Pearson correlation generally shows the correlation coefficient between variables which is in the value range -1 to 1 (-1 ≤ r ≤ 1) which was formulated by Conover [10] with:

variable and Y variable
The results of Pearson correlation calculations produce coefficient values that can be categorised as follows [11] :   In determining the level of vulnerability to lightning strikes, there are 3 steps that need to be done.f.Lightning threat level is divided into 5, namely very high, high, medium, low, and very low.The equation used is: Where: � ������ = Interval for each level of lightning strike threat ∆� = Range of lightning strike density values per year 2. determine the susceptibility level a. Calculating the percentage of land use as buildings and settlements using the equation: Where: � = Percentage of land area as buildings and settlements to the total area of the sub-district A= Total area used for buildings and settlements (�� � ) � ���� = Sub-district area (�� � ) b. Determine population density using the formula: Where: q= Population density value per district N= Total population per district (people) � ���� = Sub-district area (�� � ) c. Finding the level of susceptibility using the Simple Additive Weighting approach.The following stages can be used to determine the degree of susceptibility using the SAW method: 1).Determine the percentage value of land use area as buildings and settlements for the normalised sub-district area using the formula: Where: � ���� = Normalised land use value per subdistrict p = Percentage value of land use per subdistrict � ��� = The highest percentage of land use per sub-district 2).Determine the normalised population density value per district using the formula: Where: � ���� = Normalised population density value per sub-district � = Population density value per subdistrict � ��� = The highest population density value per sub-district 3).Calculating the preference value for lightning strike susceptibility from the percentage value of land use as buildings and settlements for the normalised subdistrict area and the normalised population density value per sub-district with the formula: Where: The land use value is considered to have a level of susceptibility two times higher than the population density value 4).Dividing the level of susceptibility of lightning strikes into 5 levels, namely very high, high, medium, low and very low using the following formula: Where: � �������������� = Interval of each level of lightning strike susceptibility ∆� �������������� = Lightning strike susceptibility preference value range 3. determine the vulnerability level a. Calculating the normalised value of lightning density per district using the formula: Where: Where: Vulnerability level and threat level are considered to have the same weight with a ratio of 1:1 c.Dividing the level of vulnerability to lightning strikes into 5 levels, namely very high, high, medium, low and very low using the following formula: Where: � ������������� = Interval for each level of lightning strike hazard ∆� ������������� = Range of preference value of lightning strike hazard Flowchart from this research below shown in Figure 2 begins with data collection in the form of population data, regional data, and lightning data and then processed to obtain the level of vulnerability to lightning strikes.

Lightning threat level
The level of lightning threat is a value obtained from the density of lightning in an area.Lightning density is the number of lightning strike in one year in an area within one km.Lightning density in a sub-district is affected by the frequency of lightning in the sub-district and the area width of the sub-district.The higher the number of lightning frequencies in an area will increase the lightning density, and the smaller the area of a district will increase the lightning density.In this study the level of lightning threat is categorised into 5 categories, namely very low, low, medium, high, and very high.The lightning density for each sub-district in 2017 to 2021 shown in Table 2. Changes in the number of lightning strikes from 2017 to 2021 resulted in various changes in the category of lightning threat level in each sub-district in the study area.In general it can be seen that the research area has a lowvery low level of lightning threat and an increase in the number of lightning strikes every year, in particular there was a spike in the number of lightning in 2019 which also caused a high level of lightning threat to occur in almost all research areas.Figure 3 is the change in the level of lightning threat each year and it can be seen that areas with a lightning threat level generally occur in West Lombok Regency and Mataram CIty.The highest threat level occurred in Selaparang District in 2019, which almost reached 340 strikes per .Figure 4 shows the total threat level from 2017 to 2021.From the distribution of lightning strike levels, it is known that the threat level of lightning strikes is relatively high in the northwestern region of the study area.Batu Layar and Selaparang sub-district has a very high level of threat of lightning strikes due to the high density of lightning in the area in the 2017-2021 range and followed by the Mataram sub-district in high level of lightning density.Geographical location and conditions in this area allow for the creation of a lot of lightning because it is located on the edge of the sea directly facing the hills around the coast..This is in line with the results of the Pratama and Negara [12] research, which concluded that CG lightning generally occurs in mountainous and coastal areas.In addition, research by Sugiyono [7], in the Lampung region, Gunawan and Pandiangan [8], in the Bali region, and Umaya [1], 2017 in the city of Surabaya also shows that the high level of lightning threat is generally close to the sea.

Lightning susceptibility level
The calculation of Lightning Susceptibility is carried out by carrying out the weighted sum of the population density factor and the percentage of the area used as a building.Population density is obtained from the total population of the district in one year divided by the area per district.The percentage of buildings that are used as buildings is obtained from dividing the area used as buildings in an area divided by the area of the sub-district.After obtaining the total density and percentage of area used as buildings in all districts, then the value of population density and percentage of area is normalised for each factor.After normalisation is carried out, then the weighted sum can be carried out with the weight of the building area which is used as a building considered 2 times more prone to lightning strikes so that the percentage weight of the area used as a normalised building has a weight of 0.67 while the weight for population density is 0.33.The preference value for lightning susceptibility for each sub-district in 2017 to 2021 shown in Table 3.The weighted sum results using the Simple Additive Weighting method for 2017 -2021 as shown in Figure 6 produce a lightning susceptibility index value per year.The value of the lightning susceptibility index from 2017 to 2021 does not experience much change and the high susceptibility index value is concentrated in the Mataram city.It can be seen that the distribution of lightning susceptibility index values is dominated by low -very low category susceptibility index values, especially in the northern and southern parts of the study area.This is because the majority of the population lives in the horizontally-middle area which is characterised by areas with a low category susceptibility index trending eastwest in the study area.The northern area of the study consists of highlands and mountains, while the southern region is dominated by the coast so that the population and level of land use for buildings and settlements are relatively smaller than other areas.
Total susceptibility from 2017 to 2021 in Figure 5 shows that the Mataram city area produces a very high susceptibility index value.This is due to the high population density and the percentage of land use used as buildings.This is inseparable from the role of Mataram city as the Capital City of West Nusa Tenggara Province so that Mataram City becomes the centre of government and economy in the Province.Changes in the value of the lightning strike hazard from 2017 to 2021 are shown in Figure 7.In 2017 the preference value for lightning threat was in the very high category in East Praya, Ampenan, Cakranegara, Mataram and Selaparang Districts.The factor causing the high value of the lightning vulnerability index in the East Praya area is due to its very high density value in 2017, while the Ampenan, Cakranegara, Mataram, and Selaparang Districts have very high lightning vulnerability index values due to the high preference value of the lightning vulnerability index in 2017.In 2018 the value of lightning susceptibility in the Batu Layar and Gunungsari sub-districts shows a high-moderate vulnerability category, this is influenced by the high number of lightning in the two sub-districts in 2018.In addition, from 2019 to 2021 there has been no significant change in lightning strike susceptibility.
In Figure 8, total lightning vulnerability levels in the study area is obtained which produces areas with very high category vulnerability index values in Mataram and Selaparang sub-districts.The main factor driving the high value of lightning vulnerability in this region is due to the high value of susceptibility and also the high average density of lightning in 2017 -2021 so that the resulting value of vulnerability is very high.In addition, other subdistricts in the city of Mataram produce lightning vulnerability index values that are in the high -medium category.The high vulnerability factor in the city of Mataram is more influenced by the high level of susceptibility to lightning in the city of Mataram due to the dense population and buildings in the city of Mataram.Overall the value of the lightning vulnerability index in the study area is dominated by areas with a very low level of lightning vulnerability.It can be seen that most of the areas in the North -East -South of the study area have a very low lightning vulnerability index, while the central region is dominated by areas with low category lightning vulnerability index values.
Lightning strike hazard distribution map is a combination of hazard factors and vulnerability factors.The hazard factor and vulnerability factor are given the same weighting so that the results of the distribution of the level of lightning vulnerability are a combination of the two.In Gunawan and Pandiangan's research, 2014 the threat level of lightning strikes is very high and the level of vulnerability to lightning strikes is very high in different locations resulting in a very high level of vulnerability to lightning strikes in two different locations.Changes in the number of lightning strikes each year can further be analysed by the factors that cause lightning, one of which is the factor of land use as buildings and settlements.Lightning itself has a tendency to strike relatively high areas compared to the surrounding area, so areas with tall buildings have a higher lightning strike rate.In Figure 9 it can be seen that the correlation level of the increase in the number of lightning to the increase in the area used as buildings and settlements is dominated by values with a high category correlation level.In total there are 14 sub-districts with high category Pearson correlation index values and 3 sub-districts with very high Pearson correlation index values.This shows that the increase in the area used as buildings and settlements has a high influence on the increase in the number of lightning in that location.

Conclusion
The location of the research was conducted in Mataram City, West Lombok Regency and Central Lombok Regency which are located between 8°04' -8°57'S and 115°49' -116°24'E which consists of 28 sub-districts with an area of 2143.61 km � (Figure.1).

Fig. 1 .
Fig. 1.Research area map.The data used in this study are: 1. Population data per District for 2017-2021 in Mataram City, West Lombok Regency and Central Lombok Regency released by the Central Statistics Agency.2. Data on area per sub-district in Mataram City, West Lombok Regency and Central Lombok Regency obtained from the tanahairindonesia.go.id. 3. Data on land use as buildings and settlements for 2017-2021 in the area of Mataram City, West Lombok Regency and Central Lombok Regency obtained from the livingatlas.arcgis.com/landcoverexplorer. 4. Lightning CG data for 2017-2021 recorded by the Lightning Detector sensor at the Mataram Geophysics Station.

1 .
determine the threat level a. Lightning data in *.ldc format is read and converted to a file in *.kml format with Lightning 2000 software.b.Furthermore, to read lightning data files in *.kml format, you can use the Microsoft Excel application, then they can be adjusted and saved in *csv format.c.Repeating the first and second steps until one month's data is obtained.Data in *.csv format in one month can be combined using Lightning Data Processing software.The same thing is also done to get lightning data in one year.d.Grouping lightning data for a year based on subdistricts using ArcGis 10.8 software.e. Calculating the value of lightning density per year using the total number of lightning in a year in the sub-district divided by the area of the area, with the formula: density of lighting in �� � � = Number of lightning strike in each subdistrict in a year � ���� = Sub-district area (�� � ) Susceptibility preference value for each sub-district � ���� = Normalised land use value per sub-district � � = Weight for land use factor (0.67) � ���� = Normalised population density value per sub-district � � = Weight for population density factor (0.33) Normalised value of lightning density per district d = Lightning density value per district � ��� = The highest lightning density value per district b.Calculating the preference value of lightning vulnerability per sub-district by carrying out the weighted sum of the normalised lightning density values per sub-district and the preference value of lightning susceptibility using the formula: Preference value of vulnerability for each district � ���� = Normalised value of lightning density per district � � = Weight for threat factor (0.5) � �������������� e = Preference value of lightning strike vulnerability per district � �������������� = Weight for vulnerability factors (0.5)

Fig. 9 .
Fig. 9. Pearson correlation graph the relationship between the area used as a building and settlement to the number of lightning strikes.

Table 1 .
Pearson correlation coefficient value category.

Table 2 .
Threat value for each sub-district.

Table 3 .
Susceptibility value for each sub-district.

1 .
Based on the results of an analysis of lightning threats in Mataram City, West Lombok Regency, and Central Lombok Regency in 2017 -2021 dominated by very low category lightning threat levels in 12 Districts namely East Praya, Central Praya, Praya, Janapria, Kopang, Batukliang, North Batukliang, Pringgarata, Narmada, Lingsar, Sekotong, and Sekarbela.Meanwhile, the lightning threat level is very high, namely Batu Layar District and Selaparang District, as well as areas with a high category lightning threat level, namely Mataram District.2. Based on the results of a lightning susceptibility analysis in Mataram City, West Lombok Regency, and Central Lombok Regency in 2017 -2021, it is dominated by a very low level of lightning susceptibility in 11 sub-districts spread across the northern and southern areas of the research area covering Gunungsari District, Lingsar, Narmada, Batukliang Utara, East Praya, Central Praya, Pujut, West Praya, Southwest Praya, Lembar, and Sekotong.Meanwhile, areas with high -very high categories of lightning susceptibility are in the City of Mataram with 4 Districts having very high categories of susceptibility including Ampenan, Cakranegara, Mataram, and Selaparang Districts, while 2 other Districts with high categories of lightning susceptibility include Sandubaya District and Sekarbela.3. Based on the results of an analysis of lightning vulnerability in Mataram City, West Lombok Regency, and Central Lombok Regency in 2017 -2021, it is dominated by a very low level of lightning vulnerability in 11 sub-districts spread across the north -east -south research area which includes subdistricts Lingsar, Narmada, North Batukliang, Kopang, Janapria, East Praya, Central Praya, Pujut, Southwest Praya, Sekotong, and Lembar.Meanwhile, areas with a very high level of lightning vulnerability are in Selaparang District and Mataram District, as well as areas with a high category of lightning vulnerability are in Ampenan District and Cakranegara District.