Environ Geol (2008) 56:335–351 DOI 10.1007/s00254-007-1169-9
ORIGINAL ARTICLE
Natural hazards in Central Java Province, Indonesia: an overview Muh Aris Marfai Æ Lorenz King Æ Lalan Prasad Singh Æ Djati Mardiatno Æ Junun Sartohadi Æ Danang Sri Hadmoko Æ Anggraini Dewi
Received: 23 September 2007 / Accepted: 18 December 2007 / Published online: 4 January 2008 Ó Springer-Verlag 2008
Abstract Central Java Province, Indonesia, suffers from natural hazard processes such as land subsidence, coastal inundation, flood, volcanic eruption, earthquake, tsunami, and landslide. The occurrence of each kind of natural hazard is varied according to the intensity of geo-processes. It is necessary to learn from the historical record of coastal inundation, flood, volcanic eruption, earthquake, tsunami, and landslide hazards in Central Java Province to address issues of comprehensive hazard mitigation and management action. Through the understanding about the nature and spatial distribution of natural hazards, treatments can be done to reduce the risks. This paper presents the natural hazard phenomena in Central Java Province and provides critical information for hazard mitigation and reduction. Keywords Natural hazards assessment Mitigation Central Java Province Indonesia M. A. Marfai (&) L. King Institute of Geography, Justus-Liebig-University, 35390 Giessen, Germany e-mail:
[email protected];
[email protected] M. A. Marfai D. Mardiatno J. Sartohadi D. S. Hadmoko Faculty of Geography, Gadjah Mada University, 55281 Yogyakarta, Indonesia L. P. Singh Geological Survey of India Training Institute, GSI Complex, Bandlaguda, Hyderabad 500068, India A. Dewi AUSAID, Yogyakarta-Central Java Community Assistance Program, 55581 Yogyakarta, Indonesia
Introduction Natural hazards are threatening events and capable of producing damage to the environment. Natural hazards occur worldwide, however, their impact is greater in developing countries, such as Indonesia, where they occur very often. According to Sutikno (2007) Indonesia is susceptible to many types of natural hazards, such as volcanic eruption, earthquake, and tsunami, because Indonesia is in collision zone of three tectonic plates (Eurasian, India-Australian, and Pacific plates), between two oceans (Pacific and Indian), and between two big continents (Australian and Asian). Meanwhile, the multiple effects of physical processes and human agency also contribute to the natural hazards each year. Flood, coastal inundation, subsidence, and landslide are very common due to the intense rainfall, frequent earthquake, steep slope on the mountainous areas, and weak geological formations. Coastal inundation due to land subsidence is considered one of the most serious problems faced by coastal urban cities in the world. In the capital of the Central Java Province, Semarang, coastal inundation due to enhanced land subsidence is a major threat for the community and coastal development. An area of more than 1,610 Ha witnesses inundation extending up to 2 km inland from the coast almost every day depending on the tidal highs. In general, the height of inundation is varying from 40 to 60 cm (Soedarsono 1996; Kobayashi 2003; Marfai et al. 2007). Meanwhile, river flooding in Central Java is also one of the most frequently occurring hazards every year during the rainy season. More than 25 regencies and cities in Central Java are vulnerable to flooding (Development Planning Board of Central Java/Bappeda-Jateng 2005). The
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magnitude of devastating impact is getting bigger and bigger, especially in the low-lying and coastal area. Java Island is located at the southern part of Eurasian plate margin. The India-Australian plate is moving northward relative to southeastern Asia, subducting beneath the southern Indonesian islands along the Java trench. As a result, Java region witnesses a number of seismic and volcanic activities. The recent earthquake of 27 May 2006 struck Java Island about 33 km south of Bantul district in the highly urbanized Yogyakarta and Central Java Provinces. About 1,057 people in Central Java Province and 4,659 people in Yogyakarta Province were killed and 50,000 people were injured due to this disaster (Leitmann 2007). In addition to earthquakes, Java Province also experiences frequent volcanic activities with 16 active volcanoes situated in the Island. Merapi Volcano, one of the most active volcanoes in Central Java Province, is amongst the most dangerous volcanoes of the world (e.g. Crandell et al. 1984; Thouret et al. 2000). Two large-scale eruptions in 1872 and 1930–1931 took the life of 200 and 1,369 persons, respectively. Most recently, on 22 November 1994, block-and-ash flows and pyroclastic surges killed 64 victims and during the small-eruptions on June 2006, the local Government evacuated 44,500 people who lived around the risky zone (Abdurachman et al. 2000; Subandriyo et al. 2007). In addition, low-lying and coastal areas are also under threat from tsunami. The recent tsunami of 17 July 2006, struck the southern coast of Central Java causing the death of approximately 668 people (Lavigne et al. 2007). Besides, landslide is the most damaging hazard in mountainous areas of Central Java Province. As a humid tropical area with very active geomorphological processes, the mountainous and hilly areas in Central Java are subjects to landslide hazards (Hadmoko and Lavigne 2007). Data recorded by Directorate Geology and Hazards Mitigation Office/DGHM (2007) reveals that more than 50 damaging landslide disasters have occurred in Central Java Province during the period 2000–2007. In view of the above background, it is necessary to learn from the historical record of coastal inundation, flood, volcanic eruption, earthquake, tsunami, and landslide hazards in Central Java Province to address issues of comprehensive mitigation plan at provincial level. This paper is intended to provide information on the magnitude and behaviour of the natural hazards phenomena in Central Java Province and critical information for decision makers and the disaster response community. This paper provides an example of multi-hazard assessment of subsidence, coastal inundation, flooding, volcanic eruption, earthquake tsunami, and landslide.
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Study area Central Java is a province of Indonesia with an area of 32,548.20 km2, which is approximately a quarter of the total land area of Java. It is situated between latitudes 6°–7°300 S and longitudes 108°300 –112°000 E (Fig. 1). The relative humidity varies between 73 and 94% with average temperature between 18 and 28°C (Bappeda-Jateng 2005). Geomorphologically, Central Java can be divided into two zones, lowlands near the northern and southern coast and mountain ranges in the centre of the region. Central Java is divided in to 29 regencies and 6 cities. Regency can also be called a rural district, while city is an urban district. The population of Central Java in year 2005 was 31,820,000, while in 1990, it was 28,516,786. Therefore, the population has increased approximately 11.6% in 15 years (Statistic of Semarang 2001). Some of the regencies in Central Java are fertile agricultural region and the primary food crop is wet rice. The rice production is growing rapidly due to the increase in irrigation network of canals, dams, and reservoirs. Other crops, such as corn, cassava, groundnuts, soybeans, and sweet potatoes, are also grown in rural areas (Engelen 1980; Van der poel and Van Dijk 1987).
Natural hazards in Central Java Subsidence and coastal inundation The use of the coastal and low-lying areas, such as in the capital city of Central Java Province, for economic activities, housing, and other human activities contribute to extensive land use change and increasing groundwater extraction leading to land subsidence (Fig. 2). It has been reported that part of the low-lying and coastal area in Semarang is sinking relative to the mean sea level (Sutanta 2002; Kobayashi 2003; Marfai and King 2007a). The subsidence has evident effects on the buildings and coastal environment. The most evident effects are damage to the road and dwelling units, overflowing of water into residential areas, permanent inundation on the coastal areas, and change in the coastline (Fig. 3). Marfai and King (2007a) have generated the rate of the subsidence map using benchmark points. From the benchmark data, it can be seen that the rate of subsidence in Semarang varies from 2 to 10 cm/year and the maximum rate is about 16 cm/year. Using the land subsidence map of Marfai and King, the vulnerability assessment of the land use along the coast can be calculated. The vulnerability has been determined in terms of the total area of a particular land use, expected to be submerged, during the years in
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Fig. 1 Central Java Province
future. Using ikonos image of 2003, four land use types have been identified, which includes: agriculture and plantation area, bare land, beach and yard, build up area, and fishpond area. The areas of different land use classes are likely to be affected by different depths of subsidence in a particular year in the future (Table 1). Table 1 reveals that the built up areas are likely to be the worst affected land in coming years with total expected area of submergence during years 2010, 2015, and 2020 being 123.08, 523.45, and 868.53 Ha, respectively. The prediction of other land use classes also indicates similar trend with increasing future years. People living in the coastal area of Semarang have been experiencing the threat of coastal inundation almost constantly. Assuming a zero-growth of population in the future years, it is estimated that [148,000 people would be suffering from inundation. The coastal inundation also affects
daily activities of the community. The coastal community is not able to go to work due to the submergence and blockade of roads in the neighborhood areas due to inundation and public services cannot be operated during the rise of seawater (Marfai 2003a, 2004; Marfai and King 2007b; Marfai et al. 2007). In the coming decades, the coastal areas might be susceptible to sea level rise (Marfai et al. 2006). These areas have high-population density and centre for industrial development and therefore, the vulnerability is very high. With the assumption that in the future years the land use pattern remains the same as the current situation, the total potential economic loss due to the coastal inundation under enhanced sea level rise in the capital city of Central Java Province is expected to be about €1,812.8 million for 120 cm of inundation and €2,330.8 million for 180 cm of inundation (Marfai and King 2007c).
Flooding
Fig. 2 Cause and impact of land subsidence in Semarang
Among the natural disasters in Indonesia, river flood is one of the most frequently occurring phenomena every year. There are about 5,590 main rivers in Indonesia, of which, about 600 have caused serious flood hazards and give the
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Fig. 3 Example of subsidence effects to the environment: a damage on the road, b damage on dwelling unit, c overflowed water into a residential area, and d permanent inundation lead to change of the coastline (dash– dot line was the former coastline). Photos: Marfai (a, c, d), and Kobayashi (b)
worst impact on social and economic conditions (Sutardi 2006). The frequency and magnitude of devastating floods and their impact are getting bigger. As an average, more than 250 people lose their lives annually. In terms of monetary loss, more than €77 million worth property, and economic and social infrastructures are damaged annually (Sutardi 2006). Major part of Central Java areas is experiencing highrainfall annually, especially in December–March (Fig. 4). When the rainfall exceeds the capacity of stream channel and drainage ditch, floods occur. People living in the lowland and riparian areas suffer the most from flooding. The drastic land use changes from forest areas to intensive agricultural land and build up area as well as the deforestation of mountains and hills contribute to increasing run off and degradation of watershed leading to flooding on the lowland areas. In addition, due to high-rainfall intensities and watershed erosion, rivers carry large quantities of sediment, which results in river regime problems as well as
river mouth clogging (Marfai 2003b; Marfai and Suprayogi 2005). Data recorded by Ministry of Agriculture (2007) reveal that there are more than 25 regencies and cities, which are vulnerable to flooding. The biggest areas are situated in Cilacap; Kudus; Brebes; Demak; and Semarang with affected area of 32,500; 22,500; 15,504; 15,061; and 15,000 Ha; respectively. Easily inundated areas in Central Java Province are distributed in low-hills, alluvial plains, and lowlands surrounding coast (Fig. 5). Total vulnerable area in Central Java Province is about 199,427 Ha. Central Java Province has more frequent flood events compared to other provinces in Java Island. For example, in year 2005– 2006, the most frequent flood events in Java occurred in East Java Province followed by Central Java with 99 and 91 events, respectively. However, the impact of flood disasters in Central Java is very severe. Ministry of public Work (2007) has summarized that 1,337 people died and 262 were missing; 211,156 houses were inundated and damaged; 635 m of roads damaged; 16 bridges damaged; 6,927 Ha of the agricultural land; and 1,230 Ha of the fishpond area were affected due to flooding (Table 2).
Table 1 Prediction of the land use affected by land subsidence process in Semarang (Ha) Land use Agriculture and plantation area Bare land, beach, and yard Build up area Fish pond area Total
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2010
2015
2020
47.06
192.85
356.32
101.36 123.08
371.93 523.45
601.29 868.53
90.50
289.28
400.86
362.00
1,377.50
2,227.00
Earthquake Java Island experiences frequent earthquake. An earthquake with a magnitude of 6.3 on the Richter scale struck the area around the city of Yogyakarta in Central Java at 05:54 hours local time on 27 May 2006. Subsequently, about 750 aftershocks were reported, with the largest
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Fig. 4 Rainfall distribution in December–March in Central Java Province (Hadmoko 2007)
recorded intensity of 5.2. Since it was a relatively shallow earthquake, the ground shaking was very intense and caused widespread destruction. More than 175,000 houses were destroyed or damaged and about 200,000 people were estimated to had been displaced and rendered temporarily or permanently homeless. Most of the private homes used low-quality building materials and lacked essential structural frames and therefore, collapsed easily as a result of lateral shaking. Distribution of the housing damage and losses is shown in Fig. 6. In addition, the earthquake also affected the infrastructure. The power distribution was disturbed due to the damage of three distribution towers; the runway of Yogyakarta Airport developed cracks and the terminal building partially collapsed. (National Development Planning Agency/ Bappenas 2006; Leitmann 2007). According to Bappenas (2006) the total amount of damage and losses caused by the earthquake was about €2.1 billion. The damage concentrated very heavily on housing buildings. Nearly 880,000 poor people live in the affected area and the number is estimated to increase by additional 66,000 and 130,000 people might lose their jobs.
Volcano Merapi is one of the most active volcanoes of Indonesia. The eruption records show a persistent activity and 33 eruptions since 1822 (Berita Berkala Vulkanologi 1990; Thouret 2000). The most violent eruptive phases of Merapi were characterized by column collapse, producing nue´es ardentes that were channelled along the west-flanks valleys
in 1822, 1872, and 1930 (Boudon et al. 1993). Even though it has erupted many times, about 1.1 million people are still living on the flanks of the active Merapi Volcano. According to Lavigne et al. (2000) about 200,000 people live at risk in areas prone to pyroclastic flows and 120,000 more live in the area along the 13 rivers, which are prone to lahars. The most recent small-scale eruptions occurred on 22 November 1994 and another during June 2006. On 22 November 1994, about 2–3 million m3 of lava dome collapsed and generated pyroclastic flows and surges of sufficient run out to strike inhabitants of the villages on the flanks of the volcano. The eruption began with steam explosions and ejection of rocks and gravels over the surface of the cone. A pyroclastic flow of hot ash, gas, and other suspended particles swept 6 km to the southwest direction. More than 6,000 people have been evacuated from the area. After 27 days on Red Alert status, on 8 June 2006 Merapi erupted and spewed a huge amount of pyroclastic flow. The pyroclastic flow reached a distance of 5 km towards the south. Again, the strong pyroclastic flow occurred on 14 June 2006, which transported more than 2.5 million m3 of the new lava dome. Two persons died during the Merapi eruption of 2006 when they were trapped in the bunker built by local government, which is located 6 km away from the Merapi summit. Fortunately, vulnerable groups like pregnant women, children/babies and the elderly were evacuated by 4 June 2006. During the Merapi eruption in 2006, 100 Ha of forest and 25 Ha of farming area and some houses were damaged (Subandriyo et al. 2007).
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Fig. 5 Vulnerability area due to flood hazard in Central Java Province (Water Resource Management Office of Central Java Province/WRMO 2007; Ministry of Agriculture 2007)
Tsunami Indonesia is situated at the junction of three tectonic plates (Eurasian, India-Australian, and Pacific plates), which makes the country vulnerable to earthquake and tsunami
hazards (Fig. 7). Tsunamis have caused severe destruction and thousands of deaths. The most severe losses were caused by the earthquake of magnitude 9.0 and subsequent devastating tsunami that struck Aceh and North Sumatra in December 2004. More than 200,000 people were killed or
Table 2 Impact of flood hazard in Central Java Province (summarized from Ministry of Public Work 2007) Province
Event
Number of damage and inundated object People killed
People missing
Housing
Road (km)
Bridge
Agricultural land (Ha)
Fishpond (Ha)
DKI Jakarta
9
3
0
513
0
0
0
0
Banten
17
1
0
3,426
1
0
1,935
0
West Java
60
508
162
13,811
12
9
48,250
5,150
Central Java
91
1,337
262
211,156
635
16
6,927
1,230
DI Yogyakarta
16
4,776
241
411,917
3
34
1,790
0
East Java
99
110
21
27,942
713
28
28,452
730
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Fig. 6 Distribution of the housing damage and losses due to earthquake in Central Java (Bappenas 2006)
missing and 500,000 had to be evacuated (Lavigne et al. 2006). Again, on the 17 July 2006, a tsunami struck the southern coast of Java, causing over 730 casualties. According to Lavigne et al. (2007), the tsunami was generated by a ‘‘tsunami earthquake’’. Tsunami earthquake means a tsunami which is produced by an earthquake and it is usually larger in comparison to the earthquake magnitude (http://www.ioc3.unesco.org/itic/contents.php?id=19). The
triggering earthquake located 225 km off the coast of Pangandaran (9.222°S–107.320°E). Almost entire south coastal areas of Central Java Province including 95 villages were exposed directly to the tsunami wave with the regencies of Cilacap, Kebumen, and Purworejo being the worst affected. In Cilacap, 142 people died, 57 missing, and 7 injured. Meanwhile, in Kebumen 12 people were killed, 46 missing, 27 injured, and about 1,388 have been evacuated (Table 3).
Fig. 7 Coastal vulnerable areas to tsunami in Indonesia (Bakosurtanal 2006)
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Table 3 Impact of the tsunami in Java, 17 July 2007 (summarized from Ministry of Public Work 2007) Regency
People killed
People missing
People injured
People to be evacuated
Cilacap
142
57
7
No data
No data
No data
Kebumen
12
46
27
1,388
49
487
Purworejo
0
No data
No data
No data
5
68
According to Lavigne et al. (2007), along the coast, the maximum height of tsunami waves before their breaking ranged from 4.2 to 8.6 m, and the measured run-up heights up to 15.7 m (Fig. 8). It is almost similar with Fritz et al. (2007), where tsunami heights and run-up distributions were uniform at 5–7 m along the coast. Even though the run-up values in Cilacap were lower than 3 m but their impact were damaging. On the other hand, Fritz et al. (2007) also found that in the certain places in Cilacap, i.e., in Nusakambangan Island, the local flow depths exceeded 8 m above terrain along the elevated coastal plain 200 m inland from beach.
Fig. 8 Run-up heights distribution along the south coast of Central Java province due to Tsunami, 17 July 2006 (modified from Lavigne et al. 2007)
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Building damage
Boat damage
Landslide Most of the mountainous and hilly areas in Java are susceptible to landslides (Marfai and Widiyanto 2002). Heavy rainfall triggers a large number of landslides each year. During prolonged rain, infiltration from the surface eventually saturates the pores in the soil leading to landslides. Many of these landslides have caused loss of lives, destruction of property and houses, and damage to infrastructures such as channel, bridge, and roads. As it is summarized by Hadmoko (2007), the landslides in Java Island tend to increase year-by-year (Fig. 9). Between 1990 and 2005, landslides caused the death of 1,112 people and wounded 395. The highest loss occurred in 2005 with 118 victims. The number of landslide events in 2004 and 2005 was similar (77 and 78 events, respectively), however, the total human losses between these 2 years increased by 60%. Meanwhile, settlement and housing in Central Java Province is growing rapidly with the increasing population. The development expands into unstable hillslope areas triggering processes for landslide occurrence. Furthermore, landslides in Central Java are also initiated by anthropogenic deforestation followed by soil and rock excavation. Due to increasing population densities and ill-planned development, more and more people are affected by landslide disasters. Data recorded by DGHM (2007) shows that between years 2000 and 2007, 57 landslide disasters have been listed in this province (Table 4). The most damaging events among these are landslide in January 2006 in Banjarnegara causing the death of 142 people and 182 houses were damaged; and landslide in September 2000 in Purworejo caused the death of 44 people and 20 people were injured as well as 77 houses were damaged. Again, in February 2000 in Brebes, a landslide killed 13 people and about 125 houses were damaged. Landslides mostly occur on the remote areas with no proper development of roads and infrastructures; therefore, it is sometimes very difficult to rescue the victims. More example of the landslide hazard is shown in Fig. 10. Figure 10 reveals landslides in Cilacap, Banjarnegara, and Purworejo. The main factors causing landslide event of 30 October 2000 in Cilacap were high rainfall intensity and deforestation on the hills areas. Twenty-nine houses and
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Fig. 9 Landslide events and related victims in Java Island between 1990 and 2005 (DGHM 2007; Hadmoko 2007)
20 m of road were damaged on the slide area. The landslide of 8 January 2006 in hill areas of more than 45° slope gradient in Banjarnegara, resulted more than 200,000 m3 material moving to the lower area and buried the villages on the foot slope. Twenty-one houses were buried. Landslide in Purworejo on 5 November 2000 caused death of 44 people, injured 22 people, and damaged 77 houses and 50 m of road (Hadmoko 2007). Spatial distribution of the susceptibility classes of landslide in Central Java is shown in Fig. 11. Some areas have high–moderate susceptibility. According to DGHM (2007), the region of moderate landslide susceptibility are the areas of high slope and escarpments in the vicinity of river banks, which show incidences of historical mass movement. The regions of high landslide susceptibility are the areas where mass movement occurs frequently. Both the old mass movement and new mass movement are still active due to high rain intensity and soil erosion.
Hazards reduction and prevention Since the coastal inundation happens throughout the year together with the land subsidence process, the local people have adapted to facing the hazard by doing some protection measures. These protection measures can be broadly categorized into structural and non-structural measures. Some structural devices such as increasing the floor level following the water level, increase the yard level surrounding the house, and construction of small dams to block water from entering the house are practiced (Marfai and King 2007c; Marfai et al. 2007). The measures include reshaping of land surface and land reclamation of the beach area, improving the dyke and drainage system, improving drainage pumping stations, and improving polder system (Public Work Department/DPU 2000). The non-structural
measures include improvement of the neighborhood area by coastal planning and management (Development Planning Board/Bappeda-Semarang 2002). Though the local government of Semarang City has also been employing structural measures to counter the impact of the subsidence and inundation, the measures have been inadequate to solve the entire coastal inundation problem within the coastal and low-lying area of Semarang (Marfai and King 2007d). Recently, the local government of Semarang has developed polder system based on the community participation (Sawarendro 2003) and is in the process of implementing comprehensive coastal land use planning and regulation to control the subsidence and the coastal inundation. Regarding flood hazard management, the government has adopted a comprehensive operational policy to mitigate flood hazard comprising five principles. These principles could be adapted and implemented on the provincial level of flood management such as in Central Java Province. According to Sutardi (2006), the five principles of the comprehensive operational policy are (1) inventory of land use changes that cause floods, review of existing land use planning, support of land use planning that minimize run off, and control land use development that minimizes run off. As an example, the city government has issued policies regarding the land use zoning and coding to control the activities within the flood-prone area. The policy also describes about what kind of activities are allowed within the flood-prone area, such as, settlement, industry, and commercial area (Dewi 2007); (2) integrated water resources management and flood control measures. Flood control measures shall consist of structural and non-structural measures with special concern to preparedness and self-reliance of the community. Some structural projects have been implemented, including improvement of a dyke system and floodwall to control flooding along the river, especially in the urban-density areas (Marfai and King
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Table 4 Landslide events in Central Java Province during 2000–2007 (summarized from DGHM 2007) No
Date
City/regency
Loss and damage Number of people Killed
Injured
Number of house and building damage
Land agriculture damage (Ha)
Road damage (m)
Irrigation damage (m)
1
20.01.2000
Sragen
0
0
30
0
0
0
2
27.01.2000
Semarang
0
0
11
0
0
0
3
04.02.2000
Banyumas
0
0
22
0
0
0
4
23.02.2000
Brebes
13
0
125
0
0
0
5
31.03.2000
Wonosobo
3
4
17
0
0
0
6
15.09.2000
Cilacap
2
0
49
0
0
0
7
07.10.2000
Kebumen
0
0
31
0
0
0
8
30.10.2000
Banyumas
0
5
27
0
4,000
0
9
30.10.2000
Cilacap
0
0
29
0
2,000
0
10
05.11.2000
Purworejo
44
20
77
0
5,000
0
11
12.11.2000
Kebumen
0
0
4
0
11,000
0
12
09.01.2001
Banyumas
0
0
52
0
20,000
0
13
08.03.2001
Purbalingga
1
0
12
0
0
0
14 15
26.04.2001 05.01.2002
Cilacap Banyumas
0 0
0 0
8 3
0 0
6,000 0
0 0
16
06.02.2002
Kudus
0
0
35
200
0
0
17
10.02.2002
Kebumen
2
0
7
0
3,000
0
18
16.02.2002
Semarang
7
0
14
0
0
0
19
06.04.2002
Semarang
0
0
3
0
0
0
20
29.04.2002
Brebes
0
0
0
0
4,000
0
21
29.04.2002
Brebes
0
0
0
100
18,000
0
22
11.10.2002
Magelang
0
0
81
0
0
0
23
13.11.2002
Banyumas
0
0
4
2,406
15,000
15,000
24
14.11.2002
Kebumen
1
4
21
0
0
0
25
23.11.2002
Brebes
0
0
20
0
0
0
26
29.11.2002
Banyumas
0
0
3
0
0
0
27
31.01.2003
Brebes
0
0
44
0
0
0
28
31.01.2003
Pemalang
0
0
45
0
0
0
29 30
02.02.2003 05.02.2003
Banjarnegara Pemalang
0 0
0 0
2 12
0 0
0 0
0 0
31
07.10.2003
Banjarnegara
2
0
8
0
0
0
32
29.11.2003
Kebumen
0
0
85
0
0
0
33
05.12.2003
Banyumas
0
0
5
0
0
0
34
08.12.2003
Banyumas
0
0
6
0
0
0
35
20.01.2004
Purworejo
13
0
5
0
0
0
36
26.10.2004
Banyumas
2
0
1
0
0
0
37
29.11.2004
Banyumas
1
0
1
0
2,000
0
38
20.12.2004
Karanganyar
0
0
19
0
0
0
39
27.12.2004
Magelang
0
0
4
0
25
0
40
01.01.2006
Purworejo
2
0
15
0
0
0
41
04.01.2006
Banjarnegara
142
15
182
0
0
0
42
07.01.2006
Magelang
0
0
9
0
0
0
43
07.01.2006
Cilacap
0
0
26
0
0
0
44
08.01.2006
Banjarnegara
0
0
21
0
0
0
45
10.01.2006
Pemalang
0
3
28
0
0
0
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Table 4 continued No
Date
City/regency
Loss and damage Number of people Killed
Injured
Number of house and building damage
Land agriculture damage (Ha)
Road damage (m)
Irrigation damage (m)
0
46
13.01.2006
Wonogiri
2
0
0
0
0
47
15.01.2006
Kebumen
0
0
58
0
0
0
48
19.01.2006
Pemalang
0
0
54
0
0
0
49
24.01.2007
Pemalang
1
0
7
0
0
0
50
10.02.2007
Jepara
0
0
5
0
0
0
51
18.02.2007
Magelang
10
0
0
0
0
0
52
01.03.2007
Wonosobo
0
0
0
0
0
0
53
16.03.2007
Wonosobo
0
0
0
0
0
0
54
24.03.2007
Puworejo
0
0
9
0
0
0
55
10.04.2007
Brebes
0
0
25
0
0
0
56
04.05.2007
Banjarnegara
0
0
0
0
80
0
57
04.05.2007
Karanganyar
1
0
0
0
5
0
2007d). In addition, the maintenance of the catchment area and upper part of the watershed system also plays an important role for the flood management. As an example, Gatot et al. (2001) introduced a system to manage rainfallrun off on the watershed for water reservoir and flood control management using rainfall-runoff harvesting in Semarang City; (3) provision of adequate urban infrastructure for drainage of settlement and solid waste disposal. For this purpose the local government of Semarang has introduced projects through the related and responsible agencies to maintain the potentially flooding rivers within the city (Dewi 2007). These projects range from canal and river channel cleaning up to improvement of waste disposal system; (4) provision of low-priced housing to resettle poor people obstructing discharge of flood waters or those living at vulnerable locations for floods; and (5) community service and empowerment of society comprising early flood warning systems, and hazard mapping and risk assessment as well as raising awareness. In this system, the government introduces flood warning to the region’s urban communities living in the flood prone areas. Data and information are collected from a network of automatic rainfall and river level monitoring stations. The recorders transmit real-time information via radio or phone to the agencies and governmental offices (Dewi 2007). Many deaths and injuries occurred when buildings collapsed due to earthquake disaster. The impact of the disaster was more severe due to the failure of meeting safe building standards in the area. Most of the damaged houses were built without structural frames and reinforcing pillars.
Therefore, the government took initiatives in reconstructing private houses to meet safe building standards and earthquake-resistant construction technique. In addition, the recovery strategies have been implemented by the Government. Damage assessment was done during the 2-weeks following the earthquake by Bappenas and others (Bappenas 2006; Leitmann 2007). For the long-term postdisaster recovery, it is also important to increase the awareness of disaster risks and the ability to coordinate the government responses. To do so, the government needs to improve the community skills and social capital through public education. Mitigation action after Merapi eruption has been implemented by the local government in Central Java through the development of the shelter and re-location. The hazard-zone map (1:100,000) has also been published by the Volcanological Survey of Indonesia (Pardyanto et al. 1987, Volcanological Survey of Indonesia/VSI-Merapi Volcano Observatory/MVO 1989). The hazard-zone map divides the volcano’s flanks and surrounding piedmont into three zones. The ‘‘forbidden zone’’, which lies at altitude of more than 1,500 m on the upper part of the volcano, is frequently affected by rockfall, pyroclastic flow, and tephra-fall. The ‘‘first danger zone’’ can be affected by tephrafall or lahars, should violent explosive eruptions occur. This area was thought to be beyond the reach of most pyroclastic flows and lava flows. The ‘‘second danger zone’’ corresponds to the radial valleys draining the volcano’s flanks, particularly toward the west and south. Lahars and water floods can devastate the second zone as far as 30 km down valley from the summit.
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Fig. 10 Examples of the landslide hazards in Central Java a landslide in Cilacap in October 2000, b landslide in Banjarnegara in January 2006, c landslide in Purworejo in November 2000. Photos: Lavigne (a), Research Centre for Disaster UGM (b), and Mardiatno (c)
According to Thouret (2000), the map has served a useful purpose for two decades. However, the improved version could now be produced since the existing map is not adequate for accurate hazard-zone mapping, particularly for lahar-prone areas. In addition, Thouret (2000) also suggested different types of hazard mapping, which includes: the hazard zone mapping at Merapi based on eruption scenarios, hazard mapping based on models and simulation, as well as hazard and risk assessment of lahar-
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prone areas. Figure 12 shows an example of the hazard map based on the eruption scenario as recommended by Thouret (2000). The devastating loss of life and damage to property due to the tsunami calls attention to the need for integrated system for hazard monitoring and assessment. One of the future challenges is the development of more advanced tsunami risk assessment and modeling (Mardiatno et al. 2007). Mardiatno has introduced a run-up model, some inundation scenarios and detailed tsunami risk assessment for the small part of the southern coast of Java. It is expected that the project would be developed to cover most of the tsunami risk area in Central Java. Coastal manager and emergency planners will be interested in determining the maximum wave run-up and the effects of inundation (flowdepth) in terms of numbers and types of injuries and deaths, and the need for response and rehabilitation activities. Furthermore, in the generation of risk should also determine hazard potential as well as damage potential, which includes objects vulnerability and value exposed to the hazard. Due to changes in the density of population and utilization of the southern coastal zone of Central Java (Cilacap, Kebumen, Purworejo, and surrounding areas), it has recently been suggested that the potential impacts of future tsunami are likely to be much greater than in the past. It is therefore necessary to determine the extent of coastal segments of Central Java Province at risk from tsunami inundation. For this purpose, the use of satellite imagery and Geographic Information System (GIS) technology will be very important (Tralli et al. 2005; Unosat 2006). The tsunami hazard map using geoinformation tools have been published for the southern coast of Java by Unosat for humanitarian relief, disaster prevention and post-crisis reconstruction (http://www.unosat.org; Fig. 13). This kind of map would be very helpful to disseminate the information of the vulnerability and hazard prone areas to the local communities and government agencies. It is therefore necessary for Central Java to have an international partnerships and cooperation to enable government and agencies to develop a broad range of observations that respond to the needs of the operational and policy communities in disaster management. For landslide hazard assessment and mitigation plan for Central Java Province, the mapping of inventory of landslides, elements at risk and vulnerability are necessary. These efforts will provide the information to support the prevention program, mitigation action, and evacuation plan. Currently, only the landslide susceptibility maps are available, that too only on small scale (\1:100.000) (Hadmoko 2007). Only limited areas have been covered with detailed landslide mapping. Landslide susceptibility maps tell only about the spatial probability of occurrence
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Fig. 11 Landslide susceptibility map of the Central Java Province (Modified from DGHM 2007 and http://www.portal.vsi.esdm.go.id)
Fig. 12 Merapi hazard map based on the eruption scenarios (Thouret 2000)
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Fig. 13 Impact of the tsunami in the southern coast of Java, an example of the dissemination of the hazard map for the humanitarian relief (http://www.unosat.org)
of landslides and therefore, have limited use in landslide management and mitigation strategy. Hadmoko and Lavigne (2007) have introduced a detailed spatio-temporal analysis for preparation of landslide hazard maps in parts of Menoreh hilly area in Purworejo. It is expected that the project would be extended to other areas, which have high-susceptibility to landslide. This work would be valuable to support the government mitigation program as well as it will be helpful to develop a landslide hazard and risk assessment model for the area. Geology, geomorphology, geomorphometry based on fine resolution digital elevation model, and elements at risk are the key factors for the empirical modeling (Marfai 2005, 2007; Hadmoko 2007). Provincial government of Central Java has introduced a guideline and comprehensive policy for disaster management: synergizing spatial planning, integrated resource management, controlling of development of new settlements, and improving preparedness of community in tackling natural disasters (Bappeda-Jateng 2005). The program involves the participation of local communities in the disaster mitigation programs because it has been realized that the chance for developing an effective disaster mitigation action is more, if it is supported by the community (Brilly and Polic 2005; Ologunorisa and Adeyemo 2005; Grothmann and Reusswig 2006; Venton and Fig. 14 Examples of the public awareness and education for landslide hazard mitigation in Central Java: a landslide warning signs, and b leaflet and poster of landslide awareness. Photos: Hadmoko
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Hansfords 2006, Marfai et al. 2007). Involvement of the local community, such as public education program will help people to understand the hazard characteristics. It is also important to empower the community by promoting, planning, and management of the indigenous disaster response activities. An attempt has been made in this regard for Purworejo regency, where public awareness and community involvement programs have been introduced by focus group discussion, distribution of leaflets, and posters, and generation of hazard warning signs for mitigation of landslide hazard (Fig. 14). In addition, as non-structural measures, the government has setup institutional framework for disaster management at national, provincial, and district/city levels. A national coordination board for natural disaster management, called Bakornas-PBP has been setup by the government. At provincial level, a coordinating unit, called Satkorlak-PBP, has been established. Furthermore, refugee treatment units called Satlak-PBP were established at the district level. These institutional frameworks have the task to plan, coordinate, and standardize the national approach for disaster management. Besides, it is also important to provide a multi-hazards assessment showing the comprehensive vulnerability and hazard area. Figure 15 shows the preliminary of the multi-hazards map on the study area.
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Fig. 15 Preliminary multihazard map of Central Java
Conclusion The Central Java Province of Indonesia experiences subsidence and coastal inundation, flooding, volcanic eruption, earthquake, tsunami, and landslide causing loss of life and damage to property, and infrastructure facilities. Comprehensive multi-hazard and risk assessment studies with participation of local communities and scientists need to be initiated by the government. The strategy of multihazard approach is crucial because the occurrence of one hazard may trigger the other. The subsidence phenomenon and coastal inundation processes need greater attention in view of the potential rise of sea level in future and its impact on communities. Detailed field measurement and observation to understand the local subsidence process are also needed and suggested to support the detailed subsidence assessment. Frequent floods have affected almost 200,000 Ha of lowland areas of Cilacap, Kudus, Brebes, Demak, and Semarang in recent years and therefore, more attention should be paid to these regencies of high-susceptibility to flood hazard. The recovery efforts due to earthquake in urban area in Central Java will be more effective by strengthening the existing social capital and public education, such as community based skills and network. It is also necessary to enforce building codes and ensure that earthquake-resistant construction techniques are used in the recovery process due to the recent earthquake disaster. The comprehensive eruptive hazard assessment of the Merapi Volcano is necessary to support the mitigation
plan. As suggested by Thouret et al. (2000), the revision of the hazard map could be developed based on reconstructing eruptive history, eruptive behaviour and scenarios, and on existing models and preliminary numerical modeling. Tsunami assessment in the coastal urban areas of the southern coastal parts of Central Java Province, such as Cilacap, Kebumen, and Purworejo, is also very important. The knowledge about tsunami among the local coastal communities should be improved through public education and training to support the evacuation and mitigation plan. Landslides are occurring every year in the mountainous and hilly areas of the province. Land use planning in the hilly areas should be implemented to support the prevention action. Preparation of landslide inventory and hazard map at large scale (1:10,000 or larger) should be attempted, which may be an essential input for preparing risk maps required for land use planning. Dissemination of the detailed landslide risk map and public awareness action is necessary to reduce the vulnerability and to enhance the community resilience capacity. Since the government is responsible for disaster management and mitigation measures, it should take prompt action for hazard mitigation and management in cooperation with concerned private sector organizations and NGOs with participation of local communities at large, by empowering facilities, resources, and infrastructures. To achieve this, a multi-disciplinary approach for the preparation of multi-hazard and risk assessment using state-of-the art GIS technologies is imperative.
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