Land Use Vulnerability towards the Flood Risk in Surakarta City

. Urban flood risk is one of the frequent disasters in Indonesian cities. It causes the urban vulnerabilities including urban land use, community socio-economic assets, urban infrastructures and buildings. The massive urban land use changes will lead to the increase of flood risk if those changes do not manage properly. In other side, the increase of flood risk is also caused by the land use vulnerability. The assessment of land use vulnerability on flood risk is an important element to identify the urban socio economic losses. Furthermore, the understanding of land use vulnerability could be an essential aspect for the urban land use plans relating to the process of urban planning. This study has purpose to assess the vulnerability of land use on flood risk in Surakarta City. This city has several rivers flowing inside urban areas, and often, the flood occurrences took place due to overflows of those rivers. This research used the deductive approach. The data and information provided by the institutional documents, and field observation. The result of the research indicated that the hazard level has more influence than the land use vulnerability level in the calculation of flood risk. Furthermore, it demonstrated that the land use vulnerability level is not certainly linier correlated to the risk level.


Introduction
The form of land use influences the urban ecological system. In general, the urbanization stimulates the land use changes from non-build-up areas to build-up areas in order to support the urban growth phenomena that are taking place. These changes have an consequence of flood risk increase [1,2]. Nevertheless, flood risk also caused by the urban land use vulnerability [3,4]. These situations indicate that the land use and flood risk have a reciprocal correlation in the urban development. The urban planning process needs the assessment of land use vulnerability on the flood risk in order to achieve the urban sustainability. The land use assessment is important element in the urban planning process [5,6].
This research seeks to identify the impacts of flood risk into the urban land use. It is the insight for urban planning process that should accommodate the flood risk existence in the city. The results of the research can be used as a reference to assess the recent spatial planning. The adequate spatial planning should consider the prediction of future flood risk analyzed through the recent empirical situation.

Study area and data
Surakarta, one of important Javanese cities, having the flood risk is due to the overflows of its river. Its geographical characteristic which is adjacent to Bengawan Solo River, and it is passed by several rivers, such as Bengawan Solo, Pepe, Tanggul, Anyar, etc. flowing inside of the city produce the risk of flooding in urban areas. Nevertheless, the existence of these rivers has the significant influences in the process of urban growth. The high densities of urban areas were growing around of those rivers. In fact, the biggest flooding occurred in 1966, and in recent times, these risks have occurred at least in 2007, 2008 and 2016. These situations become the reasons for selecting Surakarta as the case study for this research.
The area of Surakarta is approximately 44,04 km2 that cover five districts namely Laweyan, Serengan, Pasarkliwon, Jebres, and Banjarsari. These districts are divided into 51 sub-districts. This city is located approximately + 92 from the sea level. Furthermore, the urban settlement is about 65 % of city area.

Methodology
The research used deductive approach, and it used primary and secondary data. The institutional documentations related to the urban spatial planning for 2011-2031, the documentations of urban flood risk, and related urban statistics were used as the main sources. In addition, it also explored with the aerial photographs of Surakarta in 2015. Meanwhile the primary data were carried out through the field observation. It was useful to confirm the analysis being created on the secondary data.
The explanation of land use vulnerability on the flood risk is based on the theoretical perspectives related to the disaster risk. This term defines the summarization of hazard and vulnerability [9,10,11]. Hazard relates to the factors causing the damages in a disaster risk, meanwhile vulnerability means the factors being impacted by the hazard during a disaster occurrence. This research used the flood hazard identification based on the institutional documentation that has been provided by the local authority. Equations should be centred and should be numbered with the number on the right-hand side. The map above was used as the basic data of flood hazard in Surakarta. It is a substantial analysis in the Document of Monitoring of flood and landslide in Surakarta, which was created by the Department of Public Works of Surakarta in 2014. It classifies 4 (four) flood hazard levels including low, medium, high, and very high. The flood hazard classification is based on the land form analysis, and flood characteristics analysis which was provided through Public Participation Geographic Information System (PPGIS). The majority of flood hazard zone is located in the eastern area and southern area of city including several sub-districts: Jebres, Pucangsawit, Jagalan, Sewu, Gandekan, Sangkrah, Semanggi, Joyotakan, Serengan. The identification of flood hazard leads to the analysis of flood vulnerability to land use. In this research was conducted by several steps of identification and analysis. These steps include the identification of flood impacted land use, the identification of flood hazard, the analysis of flood vulnerability to land use, and the analysis of flood risk toward land use vulnerability. The assessment of flood vulnerability to the land use was carried out through the score analysis. The value of vulnerability is based on the density of land use. The high density of build-up area has the consequence of the high level of vulnerability of productive urban land use (housing, commerce and service, office, etc..). Otherwise, the high density of green space produces the low level of vulnerability. The results of flood vulnerability score are summarized, and then it is categorized based on the interval between maximum score and minimum score. The categorization of vulnerability includes very high level, high level, medium level, low level, and no level (zero), and it is divided into the average of intervals. Furthermore, the final calculation of vulnerability is the summarization between the vulnerability categorization of the number of land use classification and the vulnerability categorization of total score. The number of land use classification is also divided into the categorization of vulnerability.

V = Vts + Vlcn
Where: V is vulnerability of area Vts is vulnerability based on the categorization of total score Vlcn is vulnerability based on the categorization of land use classification number Meanwhile the results of summarization can be explained trough the following matrix (Table 4). It can be used for the calculation of risk being resulted through the hazard categorization (Hzd) and the vulnerability categorization (V).  The flood hazard impacted land use is located in 19 sub-districts. Several sub-districts have the high vulnerability due to its percentage of impacted area, and its various land use classification. The percentage of impacted land use area is comparison between the area of land use type being affected by flood, and the total area of land use type in each subdistrict. For example, the area of flood-impacted housing is compared to the total area of housing in sub-district. Those sub-districts include Banyuanyar, Gandekan, Joyotakan, Pucangsawit, Sangkrah, Semanggi, and Sewu. However, there are several sub-districts

The Classification of land use vulnerability on flooding
The identification of land use vulnerability leads to the assessment of the classification of land use vulnerability. This assessment was carried out through the calculation of transitional matrix of flood vulnerability. This matrix classifies the vulnerability score and the number of land use classification. Banyuanyar is the highest vulnerable sub-district, meanwhile Joyosuran and Pasarkliwon are the lowest vulnerable sub-districts.
However, the vulnerability category is only classified into 3 (three) levels of vulnerability. The high level of vulnerability is located in Banyuanyar Sub-district. Meanwhile Joyotakan, Semanggi, Sewu, Gandekan, Pucangsawit are the sub-districts having the medium level of vulnerability. The low level of vulnerability is located in several sub-districts including Sumber, Jebres, Jagalan, Sudiroprajan, Sangkrah, Kedunglumbu, and Serengan. The description of the vulnerability category can be seen in Figure 5.

The vulnerability of Land Use on flood risk
Based on the results of land use vulnerability analysis, 3 (three) categories of vulnerability level were identified. This result is correlated to the hazard identification. has the medium level of flood risk. This situation occurs due to the majority of vulnerability classification or hazard classification is also medium level.

Conclusion and Recommendation
The assessment of land use vulnerability to flooding was well explored using the calculation of vulnerability score and land use classification. The assessment of land use vulnerability indicates the high-density irregular housing and collector road are the most vulnerable land use on flooding in Surakarta City. Furthermore, the number of land use classification has a linier correlation to the vulnerability score. The classification of land use vulnerability on flooding in Surakarta is divided into the high level (81,92 ha), the medium level (270,27 ha), and the low level (137,50 ha). Nevertheless, the categorization of land use vulnerability on flooding is not certainly linier correlated to the categorization of risk. The research demonstrates that the level of hazard has more influence than the level of land use vulnerability for the determination of the flood risk classification. The assessment of flood risk indicates the majority of flood-impacted area has the medium level of risk (279,20 ha). The assessment of land use vulnerability on flooding is important to be implemented because it is useful to support the process of the determination and evaluation of spatial planning. The flood risk management should be also integrated to the adaptive land use on flooding in order that the sustainable city process can be achieved.