Analysis of Drought Index and Soil Infiltration to Control Fire Risk in Tropical Peatland Forest

Peatlands in Indonesia cover an area of more than 7% of the land area, around 14.95 million hectares spread over the islands of Sumatra, Kalimantan, Papua, and a small part of Sulawesi. Peatlands are made use of by establishing a drainage system and clearing land. Due to the peatland’s inability to absorb water, land fires and irreversible drying are all consequences. This also takes place in a protected forest in Liang Anggang Protected Forest. The purpose of this study is to reduce the risk of fire in Liang Anggang Protected Forest by establishing a correlation between the drought index on peatlands and infiltration data. Based on an understanding of the hydrological processes that occur in peatlands, which are characterized by reduced rainfall, high drought index values, and the soil’s ability to absorb water, especially in the dry season. From June to October, especially in September, the soil is very dry. It is vulnerable to fire. Extreme caution is required in the land management process with fire from the citizens around the area.


Introduction
Over 14.95 million hectares, or more than 7% of Indonesia's total land area, are covered by peatlands, which are found on Sumatra, Kalimantan, Papua, and a small part of Sulawesi [1].Peatland degradation is caused by human activities such as agricultural activities, drainage development, plantations, illegal logging, and land burning [2].It is caused an increase in surface runoff as well as a decrease in water seeping into the ground [3].When its dry, peatland is an flammable ecosystem [4].According to PNPB data in 2019, it is known that there has been an increase in the total area of land burned in all districts/cities in South Kalimantan from 2015 to 2019 [4].The increasing area of forest and land fires in the province of South Kalimantan is a problem that occurs every year [5].
Changes in land use are also a problem that influences drought in peatlands.This also occurred in a protected forest area located in Liang Anggang District, Landasan Ulin Utara Village.It is changed the land use plan that was previously used as a conservation area into a built-up area and plantations.The lack of water infiltration causes a decrease in the water level, resulting in drought and land fires [6].Most fires on peatlands are because of long periods of no rain and low heavy rains, so the peat, which should function as a water absorbent in the field, will lose its function [7].The aim of this study is to determine the correlation between external factor as the drought index on peatlands and the internal factor as the infiltration condition to control fire risk in Liang Anggang Protected Forest.

Keetch-Byram Drought Index (KBDI) Modification in Peat Physical Conditions
One of the internal factors prioritized in this research is the drought index.The drought index is a crucial indicator for detecting, monitoring and evaluating drought events.One of the drought index methods that can be used is to calculate the KBDIp (Keetch-Byram Drought Index) value.The KBDI drought index is an index using a number that represents the net effect of evapotranspiration and precipitation in producing a cumulative moisture deficiency in thick litter or topsoil related to the flammability of organic matter in the soil.The KBDI p calculation method is quite simple because only three modifiers are needed to calculate the value of the fire hazard level, as follows.The method of calculating this method is based on the following equation.
with: KBDIp,t : drought index today for peatland KBDIp,t-1 : previous day's drought index for peatland DFp,t : drought Factor for peatland RFp,t : effective rainfall in tropical peatland The value of the rainfall factor (RFt) is determined using meteorological data in the form of annual rainfall, and daily rainfall RFt of more than 5.1 mm/day is considered a reduction in the drought index.The drought factor for a, b, and c coefficient are as follows: with: DF p,t : drought factor (mm) for peatland wc : the water field capacity available in the coating (mm) KBDIt-1 : moisture deficiency (KBDI in t-1) Tm : daily maximum temperature ( o C) t : time increase (day) R0 : average annual rainfall (mm) a and c : coefficient, which is influenced by the average annual rainfall (R0) b : coefficient affected by evapotranspiration The nature of maturity/decomposition of peat organic matter is divided into 3 (three) types, namely fibric, hemic, and sapric types.In the field, the degree of maturity of the peat is determined by the pressing method, which can be demonstrated by looking at the yield of the liquid and the rest of the pressed ingredients by hand.Meanwhile, determining the thickness of peat is done by measuring from the top layer to the mineral soil.Sapric peat (highly decomposed organic material) is peat that has an advanced level of weathering (mature) in the field.The structure is relatively finer so that when squeezed by hand, the fiber content remaining in the hand is less than 15%, and the color is dark brown to black.Hemic peat (partially decomposed/ intermediate decomposition) is peat that has a moderate level of weathering, some of the material has undergone weathering with a brown color.The structure is coarser than sapric peat but finer than fibric peat so that when squeezed, the fiber material left in hand is in the range of 15-75%.Fibric peat (slightly decomposed organic material) is peat with an early level of weathering which is characterized by a high content of plant tissue materials or plant residues.The color is brown, and the structure is dominated by coarse fiber so that when squeezed, more than 75% of the fiber remains in the hands [8].Peat decomposition tends to have finer fibers, which can be seen in the field easily between the fingers so that under normal groundwater conditions, it is more resistant to subsurface fires.The ability of mature peat to retain water is also higher than that of immature peat.Dry peat is characterized by a permanent wilting point condition, namely at a stress of 4.2 pF, equivalent to a stress of 15 atmospheres (bar) [9].This condition occurs when the peat does not receive rain for a particular time.The effect of physical properties on the modified dryness index is presented in Table 1.The novelty of the drought index formula developed since the 2019 for El Nino phenomenon in tropical condition [4].This research was continued by including elements of peat decomposition level.The decomposition in Liang Anggang Protected Forest is fibric physical properties.The modification of a and c coefficient indicated in Table 2. Drought index classes are classified into four levels, as presented in Table 3 for low, moderate, high and extreme level.The extreme level is as the indicated as the driest condition and easy to flame.

Water Infiltration
Water infiltration rate measures the volume of water that enters the soil crevices and flows beneath the soil surface during ongoing rain, which is expressed in units of mm/hour or cm/hour [10].The infiltration rate varies from the soil, which is still dry, so the value of the infiltration rate is at a high point until it decreases to a constant point due to water saturation [11].Time measured from the beginning of the rain (hours).Infiltration rate classification according to the United States Soil Conservation Service with units (mm/hour) for very slow classification 1, slow between 1-5, rather slow between 5-20, medium between 20-63, fast between 63-127, fast between 127-254, and very fast > 254 [12].Infiltration capacity is the strength of the soil in the process of water infiltration under certain conditions [11].Maximum infiltration rate is another term used for infiltration capacity.Several things can affect infiltration capacity, namely high water content on the soil surface, soil type, moisture in the soil, soil surface conditions, and ground cover [12].
According to Horton, as the running time increases, the infiltration capacity decreases until it approaches a constant value.He also expressed the opinion that causes on the surface rather than those underground would have a greater influence on the decline in infiltration capability.Then, several factors that have an influence on reducing infiltration rates include land cover, closed soil cracks due to soil colloids and the formation of a soil crust, destruction of the land surface layer, and the removal of fine particles on the surface caused by rainwater [13].The Horton model can be expressed mathematically by following the following equation [11].

Research sites
The research was conducted at the location of Liang Anggang Protected Forest Block 1, Gambut District, Banjar Regency, and Liang Anggang District, Banjarbaru City, South Kalimantan.Based on the Public Works and Spatial Planning Office of Banjarbaru City, the Liang Anggang Block 1 Protected Forest area covers 948.59 ha, as shown in Figure 1.

Research Method
This research consists of collecting secondary data and primary data.Secondary data collection from BMKG Class 1 Banjarbaru Climatology Station for 2000 to 2021 [15].Data was collected from annual rainfall and maximum temperature.The primary data was collected from conducting surveys at research sites, determining infiltration test points, conducting infiltration tests at predetermined points using a double-ring infiltrometer and using the Horton approach to calculate the infiltration rate equation.Peatland fires in South Kalimantan are a disaster caused by human activity.The habit of people burning land, especially when it is dry, has a huge impact.Based on the analysis of the drought index developed to mitigate drought in peatlands and data on soil infiltration capacity, it can be used as a reference for controlling fires in peatlands.
Drought index analysis is an important part of mapping the level of drought at any time based on the rain that falls and the soil's ability to store water.The second analysis was carried out based on the soil's ability to absorb water by direct testing in the field.The hypothesis in this research is that with the two analyzes above, it was found in the month when the drought was maximum, so efforts were made to avoid land processing by burning during the dry months.

Results of Rainfall and Drought Index Analysis
The daily rainfall data used in this research is located at the Syamsudin Noor Banjarmasin Class II Meteorology Station.The data obtained consists of daily rainfall data every year from 2000 to 2021.Daily rainfall data from 2000 to 2021, as shown in Figure 2.
It can be seen in Figure 2 that rainfall monthly on average 216.72 mm/month.The highest rainfall in 425.36 mm/month, while the lowest in 62.8 mm/month in September.The description of monthly rainfall intensity shows that January to April experienced high rainfall intensity.Rainfall data experienced a decrease in rainfall intensity for around five months starting in May and continuing to decline sharply until September.Data increased slightly again in October and continued to increase until December.After the drought in 2019, from 2020 to 2022 there was an increase in rainfall, and in 2021, at the beginning of January there was quite a large flood.The correlation between rainfall and drought index can be seen in Figure 3.The second external factor analysis is an analysis of the modified drought index on the condition of the fibric physical properties.The results of calculating the average drought index every month for 20 years from 2000 to 2021 for the physical properties of peat can be seen in Figure 4 and Figure 5. Based on the recapitulation of the KBDI drought index modification for tropical conditions, it is divided into four levels.The first is a low drought level from 0 -200.It occurs from January to March and December.The second level is moderate (201 -300), as in April, May, and November.The third is a high level from June to July.The last level is the extreme drought level, the maximum drought index of more than 350 from August to October.Almost every day in September drought index in extreme level.

Figure 5 Total extreme drought index for 20 years
Figure 5 is based on the recapitulation of the KBDI drought index modification for physical tropical peat conditions for extreme conditions per month for 20 years from 2000 to 2021.The results show that the KBDI drought index for extreme conditions occurs from May to September.The highest number of extreme levels occurred in September at 472 days for 20 years of data.The KBDI drought index decreased from October to December.Meanwhile, January to March had a KBDI drought index for extreme conditions of 0.

Infiltration Rate Analysis
Infiltration rate testing in the field was carried out on three different land conditions at three different times.There were three tests of the infiltration test: on August 7, September 17, and October 29, 2022.Three tests were performed while keeping the limitations of tool calibration in mind so that only good enough data would be used later.In the third soil infiltration test in October, no data was obtained because the area was flooded, so in this study, only observations were used in August and September.The experiments were conducted on three types of vegetation density: first, low vegetation (bare); second, medium vegetation density (grassland); and last, dense vegetation density (forest).Analysis, a measure of the Horton methods infiltration rate, was only carried out on the data from tests 1 and 2. In the data from test 3 at GHL 1-1, there was no data from the infiltration test results because, during the test, the land conditions were waterlogged.Whereas at point GHL 2-1, there was no data on the results of the infiltration test because, during the test, there was no decrease in infiltration on the Infiltrometer (Double Ring Infiltrometer).The results of the analysis of the infiltration rate of the Horton method for tests 1 and 2 are shown in figure 5. From the results of the infiltration rate analysis presented in Figure 5, it can be concluded that at each test point, there is no significant difference between Test 1 and Test 2 (GHL 1-1) for the low vegetation (bare) in terms of infiltration rate classification as the medium rate from 3.66 to 4.86 cm/hour.From the sample in GHL 2 condition, GHL 2 -1 (bare) from tests 1 and 2, the infiltration rate was from 10.86 to 27.97 (from relatively fast to very fast).The data from GHL 2-2 (grassland) are the same for test 1 and test 2 as medium classification (3.66 cm/hour).For the point, GHL 2-3 (forest) are 27.66 cm/hour (very fast) for test 1 and 21.67 cm/hour (fast) for test 2.In the third sample, GHL 3-1 (bare) and 3-2 (grassland) are the same for tests 1 and 2. In GHL 3-1 is 2.68 -4.86 cm/hour (medium), and in GHL 3-2 is 7.26 -7.33 cm/hour (rather fast).In this study, infiltration testing could only be carried out at 6 points out of 9 observation points.For the 3 points where infiltration testing could not be carried out because the land conditions at those points were flooded, there was no reduction in infiltration rate on the Infiltrometer.

Discussion
Based on an understanding of the hydrological processes that occur in peatlands, which are characterized by reduced rainfall, high drought index values, and the soil's ability to absorb water, especially in the dry season.Rainfall of less than 200 mm/month occurs from June to October, with the lowest value occurring on average in September, which is the peak of the dry season in South Kalimantan.In line with the analysis of the drought index developed, the results showed that high to extreme drought index levels occurred from June to October, with the highest extreme occurring in September.In low vegetation density (bare) conditions, the infiltration rate is quite high, especially in September.It means that from June to October, especially in September, the soil is very dry.It is vulnerable to fire.Extreme caution is required in the land management process with fire from the citizens around the area.
Controlling land fires based on drought index analysis and the soil's ability to absorb water is in the dry months, namely June to October.It is necessary to socialize warning against burning during these months, especially in September.In September when there is almost no rain at all, so the land is very dry.The extreme dry soil that is burned has the potential to spread the fire more quickly to other areas arounds.

Conclusions
The conclusion obtained from the analysis is based on the knowledge of the hydrological processes that take place in peatlands, which are distinguished by low rainfall, high drought index values, and the soil's capacity to hold water, especially during the dry season.From June to October, there is an average monthly rainfall of less than 200 mm, with the lowest amount being in September, the height of South Kalimantan's dry season.According to the results of the created analysis of the drought index, high to extreme levels of the index occurred from June to October, with the maximum extreme occurring in September.The infiltration rate is relatively high under situations of low vegetation density (bare ground), especially in September.The soil is particularly bad from June through October, especially in September.It is necessary to socialize the prohibition on burning land during these months to control land fires at the research location.

2
In peatland droughts that trigger peatland fires, several influencing factors are internal factors, external factors and anthropogenic factors.Internal factors are influenced by the characteristics of peat soil in the form of the soil's ability to absorb water.Internal factors are influenced by the length of days without rain and the land drought index.Anthropogenic factors include human activities in the use and processing of forests and peatlands.

Figure 1 .
Figure 1.Protected forest area according to Public Works and Spatial Planning Officeof Banjarbaru City[14]

Figure 2 .
Figure 2. Monthly Cumulative Value of Daily Rainfall from 2000 to 2022 From the analysis from year 2000 to 2021 in Figure 3 shown in 2004 there was an extreme rain of 136.1 mm on February 3, 2004; in 2008, there was an excessive rain of 145 mm on March 4, 2008; in 2014, there was an extreme rain of 118.2 mm on March 21, 2014, in 2015 there was a heavy rain of 117.5 mm on April 13, 2015, in 2020 there was an extreme rain of 122.1 mm on February 18, 2020.In 2021, there was an extreme rain of 249 mm on January 14 2021.From 20 years rainfall data, the rainfall

Figure 3 .
Figure 3. Drought Index and rainfall data from 2001 to 2021

Figure 6 .
Figure 6.Infiltration Rate Analysis 1. Average annual tropical rainfall from local/local weather stations 2. Daily rainfall in a tropical climate 3. Maximum temperature in a tropical climate

Table 2 .
Climate Variables and Drought Factor Coefficients for Peat Physical Conditions