Spatial pattern change of land use change in tidal flood area of the coast of Cirebon Regency

Tidal flood is one of the threats found in the coastal areas of Cirebon Regency, especially in Pangenan, Gebang and Losari Districts. The changing coastal conditions and the changing land use have worsened the tidal flood. The purpose of this research is to analyse the spatial pattern of land use change in the tidal flood area. This study uses spatial analysis and temporal and spatial metrics. Temporal, spatial analysis is used to see changes in land use in tidal flood areas in 2002, 2009, and 2019, while spatial metrics are used to see these patterns, especially aggregation and diversity. The results of processing show that changes in land use in 2002–2019 were dominated by ponds and irrigated rice fields. The largest land use area in the tidal flood area is in ponds, but the increase has continued to occur in residential and built-up land from 2002 to 2019. Overall, the spatial metric results show that land use fragmentation in the coastal zone of Cirebon Regency in the tidal flood area is increasing. However, the development of land use in the coastal district of Cirebon Regency is low due to tidal flood.


Introduction
Tidal flood is a physical condition of a flood or a puddle caused by rising sea levels [1]. Tidal flood occurred when the level of the tide is higher than the ground [1]. One of the main causes of tidal flood is climate change. The climate change causes global sea level to increase by 3.1 mm per year, since 1990 [2]. Besides climate change, one of the major human activities that make tidal flood worse is urbanization and industrialization [3]. Urbanization and industrialization cause water need to increase, and if not controlled, can cause overexploitation of ground water [3]. Continuous groundwater pumping can cause the land to decline and the sea level increase [3].
The coast of Cirebon Regency is one of the area prone to tidal flood. Topographical conditions close to the sea cause Cirebon to be exposed to tidal phenomena and sea waves that have the potential to become tidal. Areas that are frequently affected by tidal flood are Pangenan District, Gebang District, and Losari District [4]. The 3 districts are the most common areas hit by tidal flood with frequency up to more than 3 times a year [4]. In 2018, tidal flood inundated the coast of Cirebon Regency with area of 6569 ha [5]. The tidal flood was estimated to cause loss about Rp 48,691,991 to the pond land use [6].
Increased land use change made the problem of tidal flood even worse. As much as 75 % of the mangrove forest area in Coastal Cirebon has been damaged [6]. In Pangenan, Gebang, and Losari subdistricts, mangrove forests experienced a reduction from 2004 to 2014 [6]. Besides land conversion, the Cirebon Regency coastal zone also experienced accretion and abrasion. The changes in coastline are caused by abrasion and accretion from 1954 to 2004 [6]. Changes in the coastline because of abrasion and accretion have caused the area of tidal flood that has become more widespread [7,8]. Changes in land use and tidal flood that occur need to be researched to know and analyze the affected areas.
The purpose of this research is to analyze spatial pattern of land use change in the coast of Cirebon Regency (Pangenan, Gebang, and Losari). This research uses spatial and temporal data to analyze the change of pattern in land use located in tidal flood area. The years used for analyzing the change of land use pattern are 2002, 2009, and 2019.

Methodology
The research is done in the coast of Cirebon Regency. The coastline of Cirebon Regency as a whole is located in the position of 6 º 32'30" -6 º 50' LS dan 108 º 30' -108 º 50' BT East Longitude is bordered by Indramayu Regency in the west-north and the eastern part with Brebes Regency, Central Java Province. The research area does not cover the entire area of the coast of Cirebon Regency, but only Pangenan District, Gebang District, and Losari District. The research area can be seen in figure 1.
In this study, the data used were temporal geospatial data in the coastal Cirebon Regency. The data used in this research are all secondary data. The data used is in the form of land use which is obtained from the Google Earth Pro image with the years used are 2002, 2009, and 2019, and tidal flood which is secondary data. The data used for this research can be seen in table 1.

Land use change mapping in tidal flood area
The tidal flood area used is secondary data. Secondary data used in this study are based on the results of a field survey conducted by [4]. After that, the tidal flood area in the coast of Cirebon Regency was   Land use in tidal flood areas was obtained from land use data and tidal flood areas in 2002, 2009 and 2019. The process carried out to obtain tidal flood areas is by overlay analysis. The overlay process is carried out in ArcMap 10.4 software.

Spatial patterns of land use in the tidal flood area
The spatial pattern of land use in the tidal flood area was obtained using the spatial metric method with the help of the Fragstats software. Spatial metric shows the placement and arrangement of an object on earth. The metrics used in this study are class and patch levels. The categories used are aggregation and diversity. In this metric, there are several calculation methods that will be used in this research. Each calculation method has its own function in explaining spatial patterns. Metrics used in this research are from [9]. The metric used can be seen in table 2.   In addition, the area of irrigated rice fields in the tidal flood area continued to decline in the period 2002-2019. This was caused by tidal flood which could give large losses to irrigated rice fields. Tidal flood in irrigated rice fields can reduce productivity and make the land difficult to replant [11,12]. The area of ponds in tidal flood areas decreased in 2002-2009 but increased in 2009-2019. Although located in tidal flood areas, the increase in 2019 was the most extensive than in 2002 and 2009. This is because ponds are land that is always used for the community's economy in the coastal district of Cirebon Regency. Despite of the increase in urban land use type, there is also a significant increase in pond land use type. This is due to the characteristic of the coast itself. The characteristic of the muddy coast makes the people of Cirebon Regency coastal use the area as a pond area [13]. Based on the result in table 3, the area of the pond land use type is increased by 497.67 ha from 2002-2019.

Spatial metric result
The results of the spatial metric are used to explain the spatial patterns of land use in tidal flood areas. Spatial metric processing is carried out according to the type of metric previously selected. The results of the spatial metric can be seen in the discussion below.   [10]. There are several patterns of land use change that can occur in an area such as aggregation pattern, a linear pattern, a smudge pattern, and a leapfrog [14]. Determination of this pattern can be determined by the results of spatial metric processing that has been done previously. Based on the results of spatial metric processing, it was found that the spatial pattern of land use change in the coastal zone of Cirebon Regency in the tidal flood area has a linear pattern. The linear pattern is characterized by an increase or stability in aggregation and a decrease in the level of cohesiveness in an area [14].  However, the SHDI and SHEI values on the coastal zone of Cirebon Regency have low values. The low diversity value indicates that the level of land use development in the coastal district of Cirebon Regency tends to be low. This is because the tidal flood that occurs is detrimental to areas that have been previously submerged. Although developed land and settlements have an ever-increasing value, irrigated rice fields and ponds have the greatest impact and are the widest inundation by tidal flood. Irrigation rice fields inundated by tidal floods will experience a decrease in productivity and will be abandoned by their owners. Meanwhile, tidal flood also has a big impact because it reduces the level of productivity and the condition of the waters becomes unsuitable for being used as ponds again [12,13]. Overall, the existence of urban sprawl or urbanization in the coastal area of Cirebon Regency in the tidal flood area can cause great losses. In areas that are quite often inundated by tidal flood, land conversion occurs which can make losses even greater.

Conclusion
Based on the results, it can be concluded that the coast of Cirebon Regency suffer land use dynamic. The most common land use in the area are irrigated rice field and pond. In tidal flood area however, the largest land use is still pond, but the increase happened to settlement and built-up land. The result of spatial metric showed that the fragmentation of land use from 2002 to 2019 increases and becoming more disaggregated while the diversity has small value and decreasing. The result of the spatial metric also shows that the land use pattern change has a linear pattern. The pattern can be identified by the increase of aggregation and decrease of cohesiveness.