Impacts of rainfall on peat fire during the dry season and wet dry season on degraded tropical peatland in South Sumatra, Indonesia

Peat fires on cleared and drained tropical peatlands continue to cause tremendous damage to their ecological functions, contribute to global warming, and reduce in health of local communities, where the fire incidents in 2019 and 2020 correlated with weather conditions. The research aims to determine and clarify the correlation between rainfall dynamics and the occurrence and severity of peat fires in degraded tropical peatlands in South Sumatra, Indonesia. The research was conducted by recording rainfall Indonesian Agency for Meteorology, Climatology, and Geophysics (BMKG) data, surface and peat fuel, and peat fire area primer data from 2019 to 2020. The results show that two types of weather correlate with the size of the burned area in the Ogan Komering Ilir (OKI) regency. Temporal rainfall distribution, quantity, and duration a determining factor for the transition of surface fires to peat fires, especially in the role they play in the hydrology and moisture conditions of peat and surface fuels. This study will present the effect of rainfall in the dry and wet dry seasons on peatland fires and the extent of peat fires that occurred in two years.


Introduction
Peatland ecosystems have an important role in contributing to the livelihoods of local communities and their important contribution to maintaining the global climate and other ecological functions.Indonesia's tropical peat is the largest in the world so if it is damaged it will harm human life globally.Sumatra has the largest peatland area of all other islands in Indonesia, around 43% of Indonesia's tropical peatlands are in Sumatra.Sumatra is an important concern in the management of peat, especially related to the prevention and control of peat fires in Indonesia.
2015 was the biggest forest fire disaster ever experienced by Indonesia, more than 2.5 million hectares of land and forest were burned that year [1,2].The fires are widespread and difficult to control due to the extreme El Nino climate [3].The estimated monetary losses from the fires in 2015, which amounted to USD 16.1 billion [4], reflect the significant impact of natural disasters on the economy.This figure represents the economic loss due to fires, including damage to infrastructure, forests, crops, property, business assets, and more.Indonesia's peatlands burn almost every year and cover a very large area [5][6][7].Peat fires cause tremendous damage to ecological functions.Efforts to control forest and land fires in peat involve a very large risk to resource safety and costs so efforts to prevent peat forest and land fires must always be a priority over extinguishing efforts.Ogan Komering Ilir (OKI) is one of the districts in South Sumatra which has the largest peatland area of more than 760,000 hectares, around 75% of the total area of the OKI district.The degraded peatlands in OKI experience fires almost every year [8].Cattau et al. [9] and Page & Hooijer, [10] stated that subsurface burning in peatlands does not occur naturally under normal weather and fuel conditions; on the contrary, so far human activities have mainly fuelled peatland fires.In the process, after the peat fuel on the surface is ignited, the fire goes below the surface and burns inside the peat layer.
These peat fires are less affected by wind, which leads to an indeterminate distribution, making it difficult to predict where they will burn [11].Fuel is abundant in the dry season due to peat drying and very dry weather conditions.Peat fires in tropical peatlands that have been cleared and drained continue to cause extraordinary damage to ecological functions, such as a decrease in the quantity and quality of peat as a habitat for various macro-organisms and forests, hydrological functions, reduction, and even loss of biodiversity: flora and fauna, and an increase in greenhouse gases.Emissions released into the air contribute to global climate change [12] and decrease the health of local communities.
Rainfall plays a very important role in peat fires in Indonesia [7].Even though rainfall does not directly affect the number of hotspots as an indicator of fire, it is an important factor affecting the moisture content of fuel [1].When the water content of the fuel decreases, it will increase the flammability of the fuel.In Indonesia, two types of special dry seasons may not be found in other countries, namely the true dry season and the wet-dry season.The two generally occur alternately from year to year and this causes different patterns of peat fires.In the wet-dry season, it often rains and causes a slow drying of peatland fuel so that the peat fires that occur are not as big as during the true dry season.This research aims to explain how the dynamics of rainfall affect the occurrence and severity of peat fires on degraded tropical peatlands, particularly in Indonesia.

Time and location
This research was conducted from June 2019 to December 2020.The study area is located in the Ogan Komering Ilir (OKI) District, South Sumatra, Indonesia (figure 1), precisely between 104° 20' and 106° 00' East Longitude and 2° 30' to 4° 15' South Latitude.The majority of OKI's area is peat lands and most of the land uses in OKI are secondary forests, oil palm plantations, settlements, savannas, swamp grass, swamp bushes, and others [13].Indonesia [13,14] The climate in Kayu Agung, the capital city of Ogan Komering Ilir Regency is classified as wet tropics with average annual rainfall > 2,500 mm/year and the number of rainy days and average rainy days > 116 days/year.The dry season generally ranges from May to October each year, while the rainy season ranges from November to April.Seasonal deviation usually occurs in five years, in the form of the rainy season, with an average rainfall of approximately 1,000 mm/year with an average rainy day of 60 days/year [13].

Methods
In this study, we were using monthly rainfall data from seven rainfall stations at Ogan Komering Ilir (OKI).These stations were established by the Indonesian Agency for Meteorology, Climatology and Geophysics" (BMKG), to measure rainfall in the Hellman gauge.To get the OKI's monthly rainfall determined by an average of monthly rainfall in seven rainfall observations during the dry season and wet dray season in 2019 and 2020.The peat fire data is taken from fire monitoring and control Manggala Agni OKI operation district at the same time.
The average monthly rainfall in the area is calculated by using arithmetic mean and we examine the relationship between rainfall and the extent of peat fires using correlation calculations.

Result and discussion
Monthly rainfall is commonly used to define the dry and wet season in Indonesia.Indonesia is a very wide country, consisting of a mare 17000 islands, the influence of these large-scale climate phenomena varies across the region [15].Sumatra has 2 dry season patterns; it is based on rain in the dry season period (the wet-dry season) and there is a dry season without rain (the dry season).The difference between the two is that they have different rainfall.In the wet-dry season, there are rainy days in the dry period, which has implications for peat fires.Rainfall directly contributes to the groundwater level and humidity of the air, so it affects the fuel condition.Indonesia experienced an El Nino phenomenon in 2015 which caused massive forest fires.This El Nino climate still affected several dry seasons in the following years 2016, 2017, and 2018.The large amount of fuel burned in 2015 caused the availability of fuel to decrease so much that forest fires decreased 4 in the next 3 years as well as the impact of rainfall.The incidence of forest fires rose again during the dry season in 2019 (Figure 2).2019 is a year that has a dry season while 2020 is a year that has a wet-dry season.In these two years, 2019-2020, the contribution of existing rainfall to the incidence of peat fires can be compared.At the beginning of entering the dry season, there is a gap time when peat fires fail to occur.This is because the fuel is still in the drying process to a point where it is prone to burning.According to de Groot, Wardati, & A Yonghe [16], fuel is flammable if it has 27.8% moisture content (mc).According to Kurniawan, Graham, Applegate, & Utami [8], especially based on the results of fuel research at OKI, the condition of the fuel in OKI will burn easily at mc conditions of 24.11%.
The rainfall that occurred in OKI in 2019 and 2020 has a different pattern and volume (Figures 3 and 4).From the 2019 data, annual rainfall = 2046.03mm, and the number of rainy days = 103 days.The difference in rainfall in 2020 = 2466.57mm and the number of rainy days = 155 days.This data is the result of calculating the average monthly rainfall from seven rainfall observation stations in the OKI District.Meanwhile, the average annual climate data for the Kayu Agung area, the capital city of OKI Regency, is classified as wet tropical with an average annual rainfall > 2,500 mm/year and the number of rainy days and average rainy days > 116 days/year.The dry season generally occurs from May to October each year, while the rainy season ranges from November to April [13].However, based on research by Nurhayati et al [1] In OKI District, September, and October are the months most prone to fires and prevention activities are the most critical at this time.
There is a significant difference in the number of rainy days between 2019 and 2020.The number of rainy days in 2019 was only 103 days while in 2020 there were 156 days, so the difference in rainfall in the two years is also very different (Figure 5).This shows that there are 2 dry season patterns in OKI which are characterized by different climate patterns, especially related to the presence of rainy days in the dry season.
These different climatic patterns affect groundwater levels.In 2019, based on observations, it is known that the groundwater level was -1.72 meters to -1.87 meters, while in 2020 the groundwater level was -0.10 meters to -0.30 meters.The level of the soil surface has a direct effect on the condition of the fuel above it, especially the moisture content (mc) factor of the fuel.This effect is due to the availability of water which is still abundant so that the fuel tends to have a high mc, so it is not flammable.In every fuel combustion, there are always three stages of the ignition process, namely: preheating consisting of evaporation and distillation, gas combustion, and charcoal combustion.As a result, wet or moist fuel will be difficult to ignite [17]  The dry season as common in OKI began in May each year and it is shown in the graph that the dry season in 2019 and 2020 has no deviation time.The number of rainy days shown in the graph decreased in May but in May 2019, the decline was very sharp and occurred until November, and between May and November 2019 was the period when the most peat fires occurred.In the wet-dry season of 2020, there is a very different pattern, in this period the number of rainy days is still high and affects on peat land fire scene.The total wide area of peat land fires in 2019 was 687,85 hectares and in 2020 49,9 hectares a significant difference between the 2 pattern dry seasons in OKI.
Rainfall is an important factor in determining a forest fire danger rating system (FDRS).The main scientific basis of this FDRS is meteorology, where it uses total precipitation or rainfall in a day, and noon conditions of temperature, relative humidity, and wind speed [18].Therefore, the pattern of rainfall in the two types of dry seasons in Indonesia affects the accuracy of the FDRS because the fuel wettability factor is the key to fire occurrence in addition to human activities in managing peat.
May to June is the period for fuel drying.The graph shows that rainfall has decreased but peat fires have not occurred.Therefore, during this period it is necessary to make artificial efforts to wet the peat to prevent peat fires.One of the efforts to rewet the peat can be done by closing natural and artificial canals to raise the water level and as a climate change mitigation measure [19].

Conclusions
There are 2 dry season patterns in Indonesia, namely the dry season and the wet-dry season.Rainfall dynamics in Indonesia play an important role in the occurrence and severity of peatland fires in degraded tropical peatlands in Indonesia.The dry season pattern directly influences the ground water level and moisture content of peat fuel which directly influences the number and extent of peat fire incidents in Indonesia.

Figure 1 .
Figure 1.Map of the study area in OKI District (the red color) and the Sumatera island,Indonesia[13,14] = 1 + 2 + 3 …  P = Average monthly rainfall in an area P1 = Data at the observation station 1 P2 = Data at the observation station 2 P3 = Data at the observation station 3 n = Number of the observation station The station rainfall data record in 7 stations are: P1 = Data at the observation station at the Kayu Agung location P2 = Data at the observation station at the Celikah location P3 = Data at the observation station at the Lempuing Induk location P4 = Data at the observation station at the SP Padang location P5 = Data at the observation station at the Tulung Selapan location P6 = Data at the observation station at the Pampangan location P7 = Data at the observation station at the Jejawi location

Figure 2 .
Figure 2. Graph of fire patterns during the dry and wet seasons in Indonesia, 2015-2020.