RISK MANAGEMENT OF MERAPI ASHFALL HAZARD IN MAGELANG AREA

By : Heru Setiawan, Oka Pratama, Dedy Humaidi, Selli Fidi Yani Wardani, Betti Yuniasih

I.                    BACKGROUND

Risk management means reducing the threats to life and property posed by known hazards. Risk assessment is the first step in risk management procedure. Risk assessment is undertaken to find out what the problems are. It involves evaluating and determining qualitative or quantitative measure of risk in an integrated way. The statistical analysis of risk is based on mathematical theories of probability and scientific methods for identifying causal links between different types of hazardous activities and the resulting adverse consequences. According to Kates and Kaperson in Smith (1996), risk assessment comprises three distinct steps: an identification of hazard likely to result in disaster, an estimation of the risk of such events, and an evaluation of the social consequences of the derived risk (Smith, 1996).

1.         Ashfall Hazard

Indonesia has several active volcanoes. Large eruptions of volcanoes endanger life and settlement areas of millions of people living on the slopes or on the foreland of active volcanoes. The hazard of volcanic eruption can be divided into direct and indirect hazard. Direct hazards that caused by volcanic eruption are lava flows, pyroclastic flows, lava, volcanic gases, and ashfall, while indirect hazards of volcano are rainfall lahars, flash floods, and volcanic avalanches (Naryanto et al., 2009; Abbot, 2004).

Merapi, a strato volcano administratively located in two provinces (Yogyakarta and Central Java), is one of the most active and hazardous volcanoes in the world (Lavigne et al., 2000). Merapi has explosive eruption. Explosive eruption is characterized by gaseous explosions that break rock and tear apart magma into pyroclastic debris with a wide range of dust to huge blocks and bombs (Abbot, 2004).

Merapi eruption that occurred in October, 2010 has a Plinian eruption type. A Plinian eruption not only blows ashes to heights but also volcanic gases. This eruption caused ashfall around Merapi volcano. Volcanic ash consists of tiny jagged pieces of rock and glass. Ash is hard, abrasive, mildly corrosive, conducts electricity when wet, and does not dissolve in water. Ash is spread over broad areas by wind (USGS, 2011).

Ashfall can have serious detrimental effects on agricultural crops and livestock depending mainly on ash thickness, the type and growing condition of a crop, the presence of soluble fluoride on the ash, timing and intensity of subsequent rainfall, condition of pasture and animals prior to ashfall, and availability of uncontaminated feed and water. Ashfall can adversely affect crops and livestock in a variety of ways, but it is very difficult to predict exact consequences and associated costs of potential ash damage or mitigation measures. This is especially true for large explosive eruptions that result in ashfall over large areas and for a series of small eruptions that occur months to months (USGS, 2011).

2.         Mapping Area

Wind direction to the west and southwest cause ashfall leads to Yogyakarta and Magelang. Magelang is a region that has the worst damaged caused by the ashfall. Ashfall that occurs in the Magelang area can caused crop failure and crop damage. Magnitude of the impact caused by ashfall over the agriculture led to risk assessment is necessary to ashfall hazard in agriculture. Therefore, for this assignment we choose Magelang area as our mapping area.

Magelang  area consists of two districts, Magelang City and Magelang Regency. Magelang Regency has 19 sub-regency while Magelang City has 3 sub-regency. The wide of Magelang area is 1,146,770.78 square kilometres. Merapi volcano located at the east side of Magelang area.

II.                  OBJECTIVES, PROCEDURES AND MATERIALS

1.         Objectives

The objective of this group assignment is to develop risk management for the Merapi volcanic ashfall on the agriculture in Magelang Area that caused by the 2010 Merapi eruption.

2.         Procedures

The procedures of this assignment are :

a.     Select  of the hazard type on the volcano

b.    Select of the element at risk

c.     Determine the probability of hazards (H)

d.    Determine area distribution of the H and then make a hazard map

e.    Estimate the vulnerability of the element at risk and the capacity

f.      Calculate the risk

g.     Determine the area distribution of the risk

h.    Develop an idea to manage the risk of the area concerned.

3.         Materials

The materials that is used for this assignment are :

a.     Magelang City and Magelang Regency administration map from RBI Map (Peta Rupa Bumi Indonesia / Indonesia Topographic Map)

b.    Magelang City and Magelang Regency landuse map from RBI Map (Peta Rupa Bumi Indonesia / Indonesia Topographic Map)

c.     Statistic data of Magelang City and Magelang Regency from Badan Pusat Statistik of Magelang City and Magelang Regency

III.                METHODOLOGY

In order to develop a good risk management for the Merapi volcanic ashfall on the agriculture in Magelang Area, we need to determine two things. The first one is area distribution of the risk and the second one is potential lost. These two things will give us an illustration of Magelang Area’s situation that related to Merapi volcanic ashfall. We need a hazard map, vulnerability of the element at risk and the capacity to determine area distribution of the risk.  meanwhile to calculating potential loss we need the amount of the element at risk.

1.       Risk Assessment

Risk assessment is the overall process of identifying and analyzing risk.  Risk assessment processing hazards’ characteristic within risk area, analyzing them for their potential mishap consequences and probabilities of occurrence, and combining the two estimations to reach a risk ranking.

Generic Risk Formula of Volcanic Risk Assessment (in Sutikno, 2011) :

R = Risk

H = Hazard Probability

V = Vulnerability

E = Element at Risk

C = Capacity

a.       Hazard

Ash falls have been the principal problem arising from volcano activity. In order to understand the stress reactions of agricultural plantation that lies within Magelang area surrounding Merapi, one important step is to map the hazard probability from ashfall hazard.

The degree to which areas near the Merapi are vulnerable to ashfall is varied. Based on the previous Merapi eruption in 2010, it is found that ashfall distribution could reach up to distance of 30 km from the volcano, and the ash thickness was still considered dangerous to crops.

In this assignment, hazards probability values for Magelang area have been divided into 6 (six) zones. This zonation process is conducted  using assumption that the closer an area to Merapi, the higher probability value to ashfall it has.  Ashfall hazard probability values are divided into six zones as follow:

Table 1. Hazard Probability Value

Zone	Distance from Merapi (Km)	Hazard Probability Value	Area (ha)	% of Area
1	0 – 5	1.0	1.447,73	1,26
2	5 – 10	0.8	7.108,59	6,20
3	10 – 15	0.6	13.096,69	11,42
4	15 –­­­­­­ 20	0.4	17.611,79	15,36
5	20 – 25	0.2	21.799,31	19,01
6	25 – 100	0.0	53.612,96	46,75
	TOTAL		114.677,08	100,00

In creating ashfall hazard probability zones, effect of wind is not considered. This bring results of a circular homogeneous distribution map of ashfall probability value, in which an area probability value solely regards  to its distance from merapi crater.

Hazard probability values are ranged from 0 to 1. Value of 0 shows that the area has no probability to suffer from ashfall hazard that is considered dangerous to agricultural plantation, whereas area with probability value of 1 means that this area would be exposed severely affected by ashfall hazard in time when Merapi erupts.

b.      Vulnerability

Vulnerability is defined as the degree of loss to a given element at risk (or set of elements) resulting from a given hazard at a given severity level (Coburn et al, 1994). The distinction between this definition and that of risk is important to note. Risk combines the expected losses from all levels of hazard severity, taking account also of their occurrence probability. The vulnerability of an element is usually expressed as a percentage loss (or as a value between 0 to 1) for a given hazard severity level. The measure of loss used depends on the element at risk. For example a ratio of the numbers of killed or injured to the total population, as a repair cost or as the degree of physical damage defined on an appropriate scale. In a large number of elements, like building stock, it may be defined in terms of the proportion of buildings experiencing some particular level of damage.

To be able to portray the vulnerability of ashfall in volcano hazard, on this assignment recognizes one dimensions of ashfall vulnerability: agricultural dimension. The agricultural dimension of ashfall vulnerability acknowledges agriculture vulnerability or fragility. In the case of agricultural vulnerability can be divided on three elements : paddy field, open field crop and mixed garden.

On this assignment, degree of agriculture vulnerability can be measured by the resistance of each element (paddy field, open field crop and mixed garden) on the ashfall. Paddy fielf is an element which has the highest level of vulnerability to the ashfall with a value of 1. Value of 1 means that if a ashfall occurs, 100% of paddy field cannot be harvested. Open field crops have a vulnerability degree 0.75 and mixed gardens have a vulnerability degree 0.5. This means that if the ashfall happened, half the value of mixed garden production will be lost. The following table shows vulnerability degree of each landuse.

Table 2. Vulnerability Degree

No.	Landuse	Type of Plant	Vulnerability Degree	Reaction to Ashfall
1.	paddy field	paddy	1	the entire plant dies and crop failure
2.	open field	Maize, sweet potato, and casava	0.75	Most of plants die
3.	mixed garden	Various type of fruit plant such as salacia, rambutan, guava and mango	0.5	Some of the plants die

c.       Capacity

Capacities are those positive condition or abilities which increase a community’s ability to deal with hazards. It also means by which people or organizations use available resources and abilities to face adverse consequences that could lead to a disaster. In general, this involves managing resources, both in normal times as well as during crises or adverse conditions.

The strengthening of coping capacities usually builds resilience to withstand the effects of natural and human-induced hazards. Capacity building also includes development of institutional, financial, political and other resources, such as technology at different levels and sectors of the society.

Losses suffered by farmers due to death of plants due to volcanic ashfall hazard rarely reimbursed by the government. The farmer can only count on their own financial ability to replace the plant. In this case the farmer’s financial ability can be seen as capacity.

Financial ability of Magelang city residents can be seen through their per capita income data. This kind of data can be found on Badan Pusat Statistik of Magelang City and Magelang Regency. They provide data per capita income of each sub-regency in the Magelang Area. Per capita income is average anual income of each people in certain area. From this data we can calculate a person average monthly income. Each sub-regency will have different average monthly income. However, this data is not enough, we need we need comparable data that can be used to assess how much money can be saved by the people of a district each month.  If we assume that the Magelang Area’s minimum wage (UMR/Upah Minimum Regional) which is Rp.795,000.00 per month is the minimum amount of money a person needs to meet the basic needs of every month, then we can compare it with average monthly income to determine how much money can be saved by the people of a district each month. The following table shows the comparison of those data.

Table 3. Capacity

Sub-Regency Name	Per Capita Income (Rp.)	Monthly Income (Rp.)	Saving (Rp.)	Capacity
Candimulyo	3,245,482.00	270,457.00	-524,543.00	0.2
Salaman	3,379,708.00	281,642.00	-513,358.00	0.2
Dukun	3,658,269.00	304,856.00	-490,144.00	0.3
Tegalrejo	3,903,775.00	325,315.00	-469,685.00	0.3
Bandongan	4,023,845.00	335,320.00	-459,680.00	0.3
Sawangan	4,102,240.00	341,853.00	-453,147.00	0.3
Pakis	4,186,293.00	348,858.00	-446,142.00	0.3
Grabag	4,433,219.00	369,435.00	-425,565.00	0.3
Windusari	5,030,002.00	419,167.00	-375,833.00	0.3
Kajoran	5,118,544.00	426,545.00	-368,455.00	0.3
Mungkid	5,259,787.00	438,316.00	-356,684.00	0.3
Kaliangkrik	5,272,631.00	439,386.00	-355,614.00	0.3
Ngluwar	5,430,679.00	452,557.00	-342,443.00	0.3
Secang	6,134,663.00	511,222.00	-283,778.00	0.4
Borobudur	6,219,237.00	518,270.00	-276,730.00	0.4
Muntilan	6,483,369.00	540,281.00	-254,719.00	0.4
Salam	6,569,497.00	547,458.00	-247,542.00	0.4
Tempuran	7,115,097.00	592,925.00	-202,075.00	0.4
Ngablak	8,465,657.00	705,471.00	-89,529.00	0.5
Martoyudan	11,885,500.00	990,458.00	195,458.00	0.6
Srumbung	12,542,837.00	1,045,236.00	250,236.00	0.6
Magelang Tengah	12,800,892.00	1,066,741.00	271,741.00	0.6
Magelang Selatan	16,033,532.00	1,336,128.00	541,128.00	0.8
Magelang Utara	16,208,030.00	1,350,669.00	555,669.00	0.8

The table shows a column that contains data about average amount of residents monthly saving.  Smaller savings means less ability of resident to rebuild their farm. We divide monthly income into several class to determine each sub-regency capacity value. The following table shows the classification.

Table 4. Capacity Classification

Nr.	Monthly Income Range (Rp.)	Capacity
1.	0   - 100,000	0,1
2.	101,000 - 300,000	0,2
3.	301,000 - 500,000	0,3
4.	501,000 - 700,000	0,4
5.	701,000 - 900,000	0,5
6.	901,000- 1,100,000	0,6
7.	1,101,000- 1,300,000	0,7
8.	1,301,000- 1,500,000	0,8
9.	1,501,000- 1,700,000	0,9
10.	1,701,000- 1,900,000	1,0

IV.                RESULTS

For this assignment, risk map of Merapi ashfall hazard in Magelang Area is built using a hazard map, a vulnerability map and a capacity map. Those map is made using the methodology that is explained in the preceeding part of this report.

1.         Hazard Map

This Hazard Map shows that the hazard suffered by a zone will be even greater if the distance is getting closer to the crater of Merapi volcano.

2.         Vulnerability Map

This vulnerability map shows that most of the Magelang Area’s  agricultural land are vulnerable. It is because most of the area are paddy field. Paddy plants have the highest vulnerability to volcanic ashfall.

3.         Capacity Map

This capacity map shows that Magelang City has the highest capacity value among the Magelang Area. It is due to the function of Magelang City as the centre of commercial activity for its surrounding areas. Although it has the highest capacity value, Magelang City has less agricultural land compared with surrounding areas.

4.         Risk Map

This risk map shows that most of the Magelang Area have very low risk to Merapi volcano ashfall hazard. The reason is because most of the area is located more than 25 km from Merapi’s crater. The high risk and very high risk area, although  not as large as the very low risk area, but it becomes interesting since its only located on four regency, Pakis, Sawangan, Dukun and Candimulyo regency.

These regencies are located near Merapi crater. Moreover, there are a lot of paddy field on the regencies and the capacity of these region are low. Those factors led the regencies to have high risk and very high risk value.

5.         Risk Management of Magelang Area

Resource that produced by the eruption of Mount Merapi is
ash and sand. Those materials covering on farmland with various thickness for each location depending on the distance from the center of the eruption and the wind direction and speed. Soil covered by the ash and destruction of crops that grow above the soil are the direct impact of ash fall. These impacts depend on the type, and age of the plant.

Damaged land includes two province which are Central Java and Yogyakarta. The study area is Magelang regency which is located in Central Java Province with volcanic ash events in November 2010.

From the risk map that we produced for this assignment, we can propose several ash fall risk management in Agriculture, which are:

1.   Provide guidance for communities located near or downwind of volcanoes especialy communities located on Pakis, Sawangan, Dukun and Candimulyo regency with a potential of producing ash eruptions. They should consider the potential impact of volcanic ash and plan for ways to deal with it and minimize its impact.

2.         Provide relevant information about ashfall risk management in Agriculture to the public such as :

a.         Ash that stuck on the leaves will close the stomata so that plants cannot inhale oxygen. The process of respiration and photosynthesis was disrupted. If this situation lasts long, the plants will wither and die. In addition, volcanic ash which has high sulphur content can damage soil structure.

b.        Volcanic ash brings benefits to soil fertility :

-    Volcanic ashes can be deadly to pest and vegetables because they contain some chemical elements such as sulphur that can kill caterpillars and insects.

-     Volcanic ashes contain sulphur (S) and silica (Si) that can function as a supplier of   plant nutrients.

-       Volcanic ashes contain copper (Cu) and iron (Fe) which is a microelement.

-       Volcanic ashes may facilitate the absorption of nutrients by plant roots.

-       Soil that is coated by volcanic ashes would be very rich in minerals and can grow a variety of plants well without additional fertilizers. Moreover, if the additional organic fertilizer is added into volcanic soil, it will be more fertile.

                         c.         Soil conservation can be carried out on agricultural land after volcanic eruption (ashfall)

-    After the eruption of Merapi, regular conservation of agricultural land is required. This is to improve soil permeability and aeration pore.

-     Land affected by ash and lava Merapi is a slope area. There are grooves in the field which is a trace of runoff and the occurrence of erosion.To control erosion and runoff on the ditch erosion required planting bamboo plants. Bamboo is planted at the edge of the ditch / cliff with a distance of 50 cm in a zigzag. The treatment is very effective, because bamboo grows easily, have fibrous roots that can penetrate the soil layer.

3.    Required assistance from the government in giving out the organic fertilizer and mulch in order for soil conservation. This is based on that :

a.   Land that is covered by ash Volkan with a thickness of <5 cm is conserved by mulching 1 ton / ha.

b.  Land that is covered by ash Volkan with a thickness of> 50-10 cm is conserved by applying organic fertilizer 2 tons / ha.