Mapping of Multiple Hazards in the Cilongkrang Sub-Watershed, Majalengka, Indonesia

The intensive agricultural activities in the Cilongkrang Sub-Watershed are causing environmental changes that can lead to various disasters. This study aims to map the spatial distribution of multiple hazards, including flash floods, erosion, and landslides. Three hazards selected because the critical condition of Cilongkrang Sub-Watershed as an upstream area caused the area to be prone to those hazards. The flash flood hazard model was created using the Flash Flood Potential Index (FFPI) method, which uses land use, slope, vegetation cover, and soil texture. The erosion hazard model was created using the Universal Soil Loss Equation (USLE) method with parameters such as erosivity, erodibility, slope length factor, crop management index, and soil conservation index. The landslide hazard model was created using the Spatial Multi-Criteria Evaluation (SMCE) method, which uses slope, landform, land use, and soil texture. The results showed that the dominant flash flood-prone areas were in the medium class of 1.556 hectares, the erosion tended to be very low, which was 2.699,5 tons/ha/year, and The Argapura Sub-District encompasses multiple regions that are highly susceptible to landslides.


Introduction
Human activities related to agriculture have significantly altered designated protected areas, leading to significant changes in physical characteristics such as vegetation density, groundwater saturation, and soil management.These alterations can disrupt the area's ecological balance and have long-term environmental consequences [1].The diminishing resources issue, both in quality and quantity, causes problems for many individuals and organizations.The Cilongkrang Sub-Watershed is an upstream area that functions as a catchment area, and any damage to the area will increase the risk of natural hazards [2].Vegetation, land, and water are needed to attain sustainable watershed management [3].Water is the most crucial component, given its pivotal role in the system.Its contribution started from rainfall, followed by the processes of infiltration and evaporation, and ended in the downstream area.
Therefore, it is essential to take the necessary measures to mitigate the negative impacts of intensive agricultural activities and ensure the preservation of protected areas.The hydrological 1313 (2024) 012028 IOP Publishing doi:10.1088/1755-1315/1313/1/012028 2 system alterations in the Cilongkrang Sub-Watershed caused by the massive transformation of the conservation area to agricultural land can lead to disasters such as flash floods, erosion, and landslides [4], [5].The consequences of neglecting soil and water conservation can lead to various problems, such as environmental degradation and the risk of flash floods, erosion, and landslides.
The flash floods, erosion, and landslides hazard problem in the Cimanuk Watershed is caused by the excessive land clearing for agricultural land [6].According to National Agency for Disaster Management, there were 16 floods, and 68 landslides in 2020 in Majalengka Regency.Particularly in Argapura Sub-District, there were 10 landslides in 2018, 9 incidents in 2019, and 7 incidents in 2020 [7].Meanwhile, erosion hazards happen because of land use changes that influence the soil system making it easily eroded.The disaster certainly can hamper and endanger community activities.The landslide disaster happened in Tejamulya and Argamukti Villages, blocking road access to the Panyaweyeuan Terraces in Argamukti Village.Apart from that, landslides also caused houses, and plantation areas to be buried, and six people were buried under material.
Ministry of Forestry through the decree of SK.328/Menhut-II/2009 stipulates that the Cimanuk Watershed is one of nine watersheds in 108 watersheds that fall into the disaster-prone watershed category and is one of the Priority Watersheds aimed at reducing environmental damage [8].Judging from the current land use, the environmental conditions in the Cilongkrang sub-watershed are quite apprehensive, so management and control measures related to land use are needed.The excessive land use change was caused by community farming patterns prioritizing the quantity of land by opening new agricultural land.Land use is usually only based on economic considerations without taking into account aspects of the natural balance of the land, which has an impact on reducing the carrying capacity and quality of the land.
Based on flash floods, erosion, and landslides threats, it is necessary to improve land use patterns, rehabilitate forests and critical lands, and restore watershed functions so it can increase land productivity, land carrying capacity, and water management control.These attempts can be carried out through studies and research to produce information related to the threat of flash floods, erosion, and landslides.The final form of the research can be used as input to determine the land use direction in the relevant watershed.Information from research results can also be used as a consideration for related parties in determining existing spatial planning or land use [8].

Research Method
Research activities were conducted in the Cilongkrang Sub-watershed, Argapura sub-district, and Majalengka Regency.Argapura sub-district is located in the highlands of Majalengka Regency, occupying a critical and strategic location with important environmental significance.The sub-district is located in the vicinity of Mount Ciremai, with an elevation of 500-2000 meters above sea level, with slopes from 25 to 40% [7].
The Cilongkrang Sub-watershed is a water catchment area located in an upland area with topographic characteristics dominated by mountainous and hilly reliefs.Based on these topographic characteristics, the Cilongkrang Sub-watershed has potential as an agricultural and plantation area.Most people in the Cilongkrang Sub-watershed tend to focus on terraced land management [9].This intensive agricultural activity is a major threat to land degradation that can lead to flash floods, erosion, and landslides.This research aims to map flash floods, erosion, and landslide hazards.

Flash Flood Hazard Method
The flash flood hazards model was created using the water runoff approach.The Flash Flood Potential Index (FFPI) method [10].FFPI calculations use parameters such as; slope, land use, canopy cover, and soil texture.This approach effectively identifies areas at high risk of flooding, allowing for proactive measures to mitigate potential damage.

FFPI=
(1) The development of the flash flood hazard model is a comprehensive process that involves the utilization of various data sources.The model incorporates slope information that is derived from the DEMNAS imagery from the Geospatial Information Agency.In addition to this, the model also utilizes canopy cover and land use data that are obtained from Sentinel 2B imagery.To ensure the accuracy of the model, soil texture information is gathered through field surveys.The data obtained from these surveys is further validated based on field observations, making the model highly reliable.The classification of each parameter used in FFPI was modified and the classification refers to the study of [11] because of the similarity of the geomorphology characteristic of the study area.

Land uses class
Land use significantly impacts water infiltration into the soil, which in turn affects the amount of runoff.The conversion of forests into agricultural or settlement areas results in reduced infiltration and increased runoff.It is therefore important to carefully consider land use decisions and their potential impact on the water cycle.Classification of land use for flash floods using the FFPI method can be seen in Table 1.High built-up land 10

Soil Texture Class
The sand facilitates water accumulation, resulting in erosion at specific points and the formation of a natural weir.Consequently, the conditions are conducive to flash floods, which may occur without warning.The score for each soil texture class is shown in Table 2.

Canopy Cover Class
Canopy cover classes shown in Table 3 are critical factors in mitigating the risk of flood disasters.These classes are determined by the density of vegetation cover, which plays a significant role in reducing the impact of flooding.The following is canopy cover class (Table 3):

Slope Factor
Slope affects the volume and direction of surface runoff and subsurface drainage that reaches a site.The speed of flood movement depends on the slope, a large slope causes a decrease in groundwater holding capacity and infiltration capacity, thus accelerating runoff velocity.In areas with high slope angles in mountainous areas, flash floods are more likely to occur, while low slopes in valleys and plains have little effect on flash floods.Slope classes are shown in Table 4.

Erosion Hazard Method
The erosion hazard map was generated utilizing the USLE, an equation for estimating soil loss in tonnes per hectare per year.This equation considers various parameters, including rain erosivity, soil erodibility slope factor, crop management index, and soil conservation index.Considering these factors, the USLE comprehensively assesses the potential for soil erosion in a given area.The method used to predict erosion values is USLE [12], the USLE equation is:

Rain Erosivity
In order to calculate the erosivity value for rainfall, data from the previous year -2021, is utilized.The Thiessen Polygon method is employed to generate spatial data.The formula used in calculating the erosivity value is as follows [13]:

Plant Management Factor (C), Soil Conservation Action Factor (P)
In accordance with the USDA SCS, Factor C is evaluated based on various factors such as the type and extent of existing vegetation.This information is critical to ensure effective crop management practices.Having a clear understanding of the existing vegetation is critical in determining appropriate crop management techniques that will optimize productivity and minimize environmental impacts [1].

Landslide Hazard Method
A combination of advanced technologies was used to create the landslide hazard map of the Cilongkrang sub-watershed.The Sentinel 2B imagery was utilized to gather land use information, while the slope information was extracted using DEM data from DEMNAS imagery which was provided by the Geospatial Information Agency.Additionally, the DEMNAS imagery was used to gather relief and landform data.Field observations are needed to ensure accuracy and were conducted to validate the slope, terrain, land use, and soil texture data [15].After gathering the data, it was then classified and assigned weights based on expert opinions [16].The weight values and scores were obtained from experts using the Analytical Hierarchy Process (AHP).This approach ensured that the data was processed accurately and efficiently, creating a dependable landslide hazard map.SMCE method created a landslide hazard model for the Cilongkrang Sub-watershed.The model considered factors such as; slope, soil texture, land use, and landform.

Flash Flood Hazard Model
The flash flood hazard map (Figure 2) provides clear evidence that several regions exhibit high levels of flash flood hazards due to certain factors.These areas are mainly in the mid-slope, upper-slope, and crater regions.The inter-volcano and volcanic foot plains are also considered vulnerable since they are close to river channels.On the other hand, a medium level of hazard areas can be found in all landforms.In contrast, the low-level flash flood hazard areas are mostly found on the volcano's foot plains and middle slopes.The following is the flash flood hazard map (Figure 2): Figure 2. Flash Flood Hazard Map Based on Figure 2, the distribution of flash flood hazard levels for low, medium, and high classes is 1.217 ha, 1.556 ha, and 1.003 ha, with an area percentage of 32%, 41%, and 27% respectively.The primary land uses within the research area consist of residential and plantation activities.These human settlements and plantations have expanded to the upstream area increasing the flash flood hazards threat.
The study area has a dominant loamy sand texture, with a high proportion of clay, making it difficult for water to seep into the soil.This particular soil composition makes it quite arduous for water to penetrate the soil.Consequently, surface runoff is significantly increased, leading to the IOP Publishing doi:10.1088/1755-1315/1313/1/0120287 exacerbation of erosion.The accumulation of soil at certain points in the area has resulted in the formation of a natural weir.The clay layer present in the soil acts as a barrier, thereby inhibiting the flow of water.
The Cilongkrang sub-watersheds, located upstream on Mount Ciremai, have a rugged relief slope prone to flash floods due to natural weirs.The slope conditions determine the water flow velocity and high erosion processes can cause natural weirs to form.The slope can decrease the cross-sectional area of the river or the river profile, increasing the likelihood of flash floods in mountainous regions.Moreover, the steep slopes make the area prone to flash flood hazards, resulting in a high FFPI index.

Erosion Hazard Model
The USLE method is a widely used tool for assessing soil erosion hazards.This method employs a mathematical model that takes into account various factors such as slope, rainfall intensity, soil type, and land management/conservation practices [17].By considering these variables, the USLE method is able to accurately predict the likelihood and severity of soil erosion, enabling land managers and policymakers to implement effective erosion control measures.The outcome of the USLE method can be generated into an erosion hazard map (Figure 3) and divided into five classes (Table 6).The map or table shows that Cilongkrang sub-watershed is dominated by very low-class erosion.

Figure 3. USLE Method Erosion Hazard Map
The primary land uses within the research area consist of residential and plantation activities.These human settlements and plantations have expanded to the upper regions of the Cilongkrang rivers, leaving the upstream area hazardous to erosion.Based on Figure 3, the distribution of erosion hazard levels for very low, low, medium, high, dan very high classes respectively is 189,36 ha, 1.577,33 ha, 907,32 ha, 641,33 ha, and 3.775,65 ha with an area percentage of 5%, 42%, 24%, 17% and 12% respectively.Based on the survey with the local farmers the usage of fertilizer requires a greater amount than usual, this phenomenon indicates severe erosion in the Cilongkrang Sub-Watershed.Normally, fertilizer is used once a week, but due to the erosion that occurs in the Cilongkrang Sub-Watershed, farmers need to fertilize their farms twice every week.The high rate of erosion can also be seen from the murky river water even though it is in the upstream area.

Landslides Hazard Model
The Landslide hazard model provides an estimate of landslides by integrating several key factors.These factors include slope, terrain, land use, and soil texture data.Based on the results of the landslide hazard map (Figure 4), the distribution of landslide hazard levels for very low, low, medium, high, dan very high classes respectively is 687,9 ha, 568 ha, 1.144 ha, 969,28 ha, and 406,098 ha, with an area percentage of 18%, 15%, 30%, 26% and 11% respectively.Based on a survey of local residents, In several cases, landslides closed roads and occurred at tourist locations such as Panyaweuyan terraces.The landslide hazard map was then validated with the Regional Disaster Management Agency record 2022, there was a distribution of landslide events in the study location, including 1 event landslide at a very low hazard level, 6 event landslides at a medium hazard level, 2 event landslides at a high hazard level, and 5 event landslides at a very high hazard level.Overall, the Argapura Sub-District comprises various areas that are prone to landslides.The causes of landslides in Argapura are caused by several factors, including the slope of the land, the shape of the terrain, the texture of the soil, the land use, and the landform.The soil composition in this area is predominantly clay, which poses a considerable threat of landslides during heavy rainfall.Furthermore, any alterations in the land use of the surrounding forests can significantly aggravate this risk, making it imperative to take necessary measures to prevent any potential hazards.Therefore, it is critical to take the necessary precautions to ensure the safety of the inhabitants of these villages.

Hazards Analysis Model
The flash flood model shows that areas with high slope value, built-up, low density of vegetation cover, and composed of parent materials or bedrocks tend to have a high class of flash flood.This model is quite similar to a model developed by [18], where areas with high slope value tend to have a higher class of flash flood because water has limited time to infiltrate, so the velocity will increase and get even higher by the time it goes down [19].The existence of built-up areas, low density of vegetation cover, and surfaces with exposed parent materials also have similar influences because they can limit the ability of water to infiltrate into the grounds [20]; [21]; [22].
Similar to the flash flood model, the erosion model shows a high class of erosion located in areas with high slope values and limited vegetation cover or bare land.Areas with high slope values tend to IOP Publishing doi:10.1088/1755-1315/1313/1/0120289 have high water velocity when it comes to rain, which can erode soil layers [19].The existence of bare land and limited soil conservation action also make the water flow easily with high velocity [23].Thereafter, the presence of regosol soil type also has a role in the high class of erosion because it is sensitive to erosion [24].
The landslide model also shows areas with high slope values tend to have a high class of landslides.The landslide model has a similar class distribution to the landslide model developed by [25], where areas with a high slope value tend to have unstable surfaces that can be removed by water easily [26]; [27].Therefore, these areas are identified or classed as a high class of landslide.
Furthermore, from the modelling results, it can be inferred that areas with high slope values are prone to multi-hazards, namely flash floods, erosion, and landslides.Consequently, these areas must be managed carefully, so it is necessary to conduct advanced research to identify the kind of measurement or management action to be implemented in the future.

Conclusion
Argapura District has been designated as one of the Regency Tourism Strategic Areas (KSPK) based on ecotourism with a development theme in the form of conservation education and nature recreation.Determining the area as a strategic tourism area aims to strengthen the function of service centers and protect potential tourism resources.The types of tourism that are superior in the Argapura tourist area are mountain natural tourism, culture, and agro-tourism.The tourism potential in Argapura District is influenced by its unique topographic conditions.This unique topography not only provides tourism and agricultural potential, but also poses the threat of flash floods, erosion, and landslides.Taking into account the existing threat of disasters, regional regulations regulate the development and services of tourism facilities and infrastructure based on disaster mitigation.
The results of flash flood, erosion, and landslide vulnerability modeling are expected to be able to assist in tourism activities so as to make the strategic tourism area of Argapura an ecotourism area that is resilient to landslide disasters.It is hoped that the results of disaster mapping can be used as input to maximize ecotourism potential and increase superior tourist attractions while maintaining the identity and uniqueness of the Argapura tourist area in a sustainable and competitive manner.

3 Figure 1 .
Figure 1.Map of Study Area