Valuing hybrid engineering approach: ecosystem and structural based DRR using InVEST model of coastal zone Sikka Flores-Literature Review

The effectiveness and long-term viability of implementing eco-DRR are heavily influenced by the regional context, including factors such as geographical locations, circumstances, and features of risks. The implementation of eco-DRR measures in coastal areas is effectively mitigating the hazards posed by high waves and other hydro-meteorological events, including storm surges, erosion, and coastal floods. The study was carried out within the framework of mangrove forest development as a means of combined protection and hard structural intervention. The success and efficacy of this endeavor rely on various circumstances, such as the magnitude of the large waves and the characteristics of the nearshore bathymetry, which dictate the extent to which the waves reach the coastline beach. In order to achieve optimal effectiveness and provide prompt safeguarding, it is necessary to employ a hybrid approach that combines ecosystem-based disaster risk reduction (DRR) methods with physical structures. This is because non-structural measures, such as ecosystems, inherently require time to grow and are highly susceptible to destruction from waves, rock debris, and water currents. Nevertheless, the ’hybrid approach’ or amalgamation must be formulated in a manner that does not engender novel or distinct dangers in various areas. This study seeks to conduct a comparative analysis of studies on Eco-DRR (Ecological Disaster Risk Reduction) focusing on high waves and other hydrometeorological risks in coastal areas. The objective is to develop a hybrid model that combines Eco-DRR and engineering effectiveness evaluation for disaster risk management, specifically for the Sikka Flores coastline area.


Introduction
Sikka District is one of the districts on Flores Island.This district has 18 islands.The geological structure is considered unstable because there are seven fault lines that are still active in the 10o-30o NE direction.The capital city of Sikka, namely the Maumere city and other densely populated areas located in a lowland morphological landscape, along the north and south coastal zone with a slope of between 0% -5% [1].
Sikka District has ten hazard types [2], including several hydrometeorology-related hazards such as tidal waves, abrasion, typhoons/cyclones, and coastal floods [3].Sikka District also has various threats to both the landscape and agriculture due to short but very heavy rainfall, widespread erosion, tropical cyclones originating from the Banda Sea and the Arafura Sea from December to April and sometimes 1314 (2024) 012029 IOP Publishing doi:10.1088/1755-1315/1314/1/012029 2 being the center of strong wind storms.that hit Sikka.The winds were very strong and there was a big flood, causing flooding, destroying food crops, and impacting food shortages [4].
The area with the highest population density is located in an area that has the highest level of risk and most inhabitants are located in a coastal zone area [5].Ecosystems in coastal areas act as barriers against coastal hazards such as storm surges, erosion, and flooding.Coastal mangroves and other coastal forests attracted global attention since it was reported reduced the impact of the 2004 Indian Ocean Tsunami.Post-tsunami findings strengthened evidence that coastal mangrove forests reduced the destructive impacts of natural disasters [6], [7], reduction of tidal wave energy, and tsunami energy [8]- [10].Subsequent studies carried out following the 2004 Indian Ocean Tsunami have furnished proof of the vital significance of coastal forests and mangrove plants in safeguarding lives, resources, and infrastructure against coastal dangers.Strong natural obstacles like sandbanks (accompanied by community plants, including coconut palms) and barrier islands diminish wave energy and function as deterrents against waves, rip currents, storm surges, and tsunamis [11].
Although there is data supporting the numerous advantages of ecosystem-based disaster risk reduction (Eco-DRR) techniques, such as their cost-effectiveness, their implementation has not been extensively adopted.
Cities are commonly situated in coastal areas or deltas, which provide convenient access to economic trade and abundant natural resources.However, they are also typically vulnerable to natural hazards.Urbanization frequently leads to heightened exposure of vulnerable individuals and assets in the coastal area, rendering them more susceptible to catastrophic events [12].
Eco-DRR can be applied to hydrometeorological and non-hydrometeorological hazards, coastal forests can be applied to reduce storm surges and tsunami waves [13].Coastal forests are thought to have partially protected coastal communities from the impacts of coastal hazard especially tsunami [14].Eco-DRR is widely acknowledged as a multifunctional method that effectively reduces the risk of disasters while also enhancing the livelihoods and well-being of communities on a worldwide scale.Eco-DRR is an economically efficient, environmentally sustainable, and socially beneficial approach.The effectiveness of Eco-DRR initiatives is enhanced by the implementation of livelihood enhancement methods.These strategies promote community awareness and engagement, which are crucial factors for ensuring long-term success and sustainability [15].Eco-DRR can use to reduce the risk of various hazard such as high waves, coastal flooding, abrasion, and tsunamis [16].
An analysis of literature on eco-DRR reveals that the effectiveness and long-term viability of this approach are strongly influenced by the specific regional circumstances, including geographical factors and the simultaneous occurrence of hazards.Developing a combination/hybrid approach of hard and soft structures is essential, as natural ecosystems require a significant amount of time to form.Contemporary research highlights the advantages of utilizing combination models or 'hybrid techniques'.It is crucial to guarantee that the hybrid approach's design does not introduce new or varied dangers in various areas [15], [17].
Eco-DRR study generally examined the impact of coastal vegetation (i.e.mangroves, coastal forests), coral reefs and seagrass.The forests mitigate wave hazards and highlighted that all these ecosystems were to some extent effective in reducing the sea energy of surge waves, storm waves and tsunami waves [15].Evergreen forests on the coastal zones reduce tsunamis [18], provide numerous ecosystem services, many of which contribute to disaster risk reduction (DRR) along tropical coastlines [19].The role of ecosystems in protecting people lifes and their assets from disasters at low intensity but high frequency events that mostly meteorological is relatively well established [15].
The primary challenge in establishing empirical data on the role of ecosystems in safeguarding against specific threats lies in its dependence on local circumstances.This hinders the ability to reproduce and expand the same acts in different areas and get identical outcomes.The heterogeneity of environmental and geomorphic factors that contribute to the effectiveness of ecosystems in mitigating disaster risk in a particular location may not be applicable in a neighboring area just a few kilometers off [20].The INVEST (Integrated Valuation of Ecosystem Services and Tradeoffs) coastal vulnerability method can be employed to address these challenges and constraints [21], [22].
The aforementioned conclusion serves as a motivation to carry out a comprehensive examination of 3 hybrid Eco-DRR and structural models in different locations, utilizing the INVEST technique for disaster risk reduction.Subsequently, a comparable valuation model will be developed and implemented in the coastal zone of Sikka Flores.This study aims to develop a hybrid Eco-DRR and Structural model for assessing hydrometeorological hazards utilizing the INVEST coastal vulnerability method.The model will be adapted for application in the Sikka Flores region.According to the 2012 Sikka catastrophe Risk Study (KRB), there were 8 catastrophe hazards that were classed as high risk.
These risks include extreme weather, extreme waves and abrasion, floods, landslides, tsunamis, earthquakes, forest and land fires, and drought [2].Sikka district also suffers from annual hydrometeorological hazards such as storm surges and high waves [23]- [25].The most inhabitants located in the coastal zone area make the risk higher, the map in picture 1 shows settlement risk in the coastal zone [5].Coastal zone disaster risk can be mitigated through structural and non-structural measures.Structural efforts have aim to reduce the energy of acean waves to coastal areas.Structural measures can be divided into two groups: natural and man-made [16].
1. Natural, such as the planting of green belts (coastal forest, mangrove, coconut plants), along coastal areas and the protection of coral reefs.2. Artificial, a. construction of breakwater, seawall, parallel breakwater infrastructure to withstand tsunami and hydrometeorological hazard b. strengthening the design of buildings and others with the implementing tsunami-resistant building techniques and disaster-friendly spatial planning by retrofitting or relocation.Non-structural measures are non-technical efforts that involve adjustments and arrangements regarding human activities to be in line and in accordance with structural mitigation efforts and other efforts [16].These non-structural efforts include, among others laws, regulations, policy governing natural disasters, disaster mitigation training and simulation,counseling and socialization, and development early warning system.
Various coastal ecosystems, including coral reefs, mangroves, coastal forests, and coconut palms, serve as protective barriers against coastal hazards such as large waves, storm surges, erosion, and flooding [6].Indonesia has adopted ocean hazard mitigation strategies that utilize a nature/ecosystembased approach by establishing coastal forests as protecting green belts in various places.This strategy enhances the coastal environment by utilizing ecosystem services to reduce the impact of future tsunamis, while also generating various economic advantages for local residents.The numerical analysis findings indicate that the inclusion of a greenbelt with a width of 50 meters can lead to a reduction of 13.57% in the maximum depth of flooding and an 18.4% decrease in the maximum speed of a tsunami [26].Approximately 50% of mangrove trees with a trunk diameter ranging from 20 to 25 cm have the ability to withstand a tsunami measuring less than 6 to 7 meters in height.However, these trees will not be able to survive if the tsunami reaches a height of 7 to 9 meters or beyond it.A computer model demonstrated that a coastal forest spanning 500 meters can significantly decrease the maximum extent of tsunami flooding by 38%.Additionally, the hydrodynamic force acting on the mangrove forest is decreased by 70% when the tsunami reaches a height of approximately 3 meters.A forest that is 10 years old will effectively mitigate the effects of a 3 meter tsunami, whilst a forest that is 20-30 years old will provide ideal reduction of the impact caused by a 4 meter tsunami.
Although the ability of mangrove forests to reduce the impact of tsunamis above a height of 4 m cannot be assessed, coastal mangrove forests need to be maintained continuosly to ensure their mitigation effectiveness [27].A numerical model in Yogyakarta shown the performance of coastal pine tree forests reduced tsunami height of a maximum 4 meters.The results showed that a 100 meter wide coastal pine (Casuarina equisetifolia) forest with a density of 4 trees/100 m2 and a trunk diameter of 0.2 meter can reduce the inundation flux, inundation depth and inundation area by 17.6, 7.0 and 5.7%, respectively.This means, the ability of mangrove forests, pine forests to reduce inundation flux is more significant than its effect in reducing inundation depth [18].
The effectiveness and immediate protection in some contexts came from combination of hard (structural) and soft (ecosystem) structures.Ecosystems naturally take time to develop, facilitating better decision-making and prioritization of options for coastal adaptation, there should be a continuous and increasing incorporation of traditional engineering and ecological approaches [28].The structural gray measures, and in particular hybrid approach can be more attractive to the at-risk public [29].Hybrid solutions may be more successful and cost-effective than green infrastructure alone [30].The optimal approach is to integrate ecosystem investments with other effective solutions for disaster risk reduction, such as structural hard engineering.While investing just in an ecosystems strategy is not a comprehensive answer to disasters, it should be employed in conjunction with other robust risk reduction methods.Ecosystem thresholds can be surpassed based on the kind and severity of hazard events and/or the condition and vitality of the ecosystem, potentially resulting in insufficient protection against the impacts of hazards.For instance, mangroves may offer little defense against tsunamis and storm surges [31].
The vegetation lack of strength, have limited ability to reduce the energy of giant tsunami and storm waves.Hybrid engineering approach which are combination of ecosystems and engineered infrastructure used to reduce disaster risk in identified places that are highly vulnerable to natural disasters.Engineered structures can be used to reduce wave energy and control floating debris accumulation.The effectiveness of ecosystems and engineered structures may change with the orientation or arrangement of the vegetation and the type of structure used.[17].The most optimal disaster risk reduction is a hybrid effort of both ecosystem-based efforts (EcoDRR) combined with structural mitigation efforts.Thus, there are several options for disaster risk reduction efforts, either pure EcoDRR, pure structural mitigation, or a hybrid combination of EcoDRR and structural [29].
Geographic information methods, such as spatial-temporal simulation modeling and spatial multicriteria evaluation, are employed to assess and track the potential impacts of different development scenarios on vulnerability to natural hazards.This includes considering various combinations of hybrid engineering, ecosystem-based, and other non-structural measures for reducing risks [32].The utilization of GIS and remote sensing satellite image technologies facilitates the evaluation of destruction caused by natural calamities.Computer simulations utilizing numerical models facilitate the testing of theories on protective mechanisms and the prediction of risk [10].The InVEST (Integrated Valuation of Ecosystem Services and Tradeoffs) method is a GIS-based approach that may be employed to assess the economic worth of ecosystem services related to risk reduction [33], [34].
The InVEST model is geographically explicit, utilizes maps as data sources, and generates results in either biophysical (e.g., metric tons of carbon sequestered) or economic (e.g., net present value of carbon sequestered) terms.InVEST is capable of evaluating ecosystem services that contribute to the provision of various services that are crucial, such as the production of goods (e.g., food), lifesustaining processes (e.g., water purification), and conditions that enhance quality of life (e.g., recreational opportunities), as well as conservation possibilities (e.g., preservation of genetic diversity for future utilization).
InVEST is a method that can be used to evaluate the combination of ecosystem-based and structural approaches in the coastal region of Sikka Flores.The Sikka Flores government, in partnership with community-based risk reduction, has begun implementing a hybrid strategy, as depicted in Figures 2 and 3. From the aforementioned explanation, it is evident that numerous research have been conducted on the subject of combining ecosystem-based and structural measures in a hybrid approach, along with the utilization of the INVEST technique for evaluation.Nevertheless, there have been few studies that have investigated the evaluation of combined ecosystem-based and structural strategies for reducing hydrometeorological risks using the INVEST technique, specifically in the Sikka Flores Coastal Zone of Indonesia.

Methods
This research was conducted in three stages.The first stage begins with a literature review.Literature review processed in-depth analysis and evaluation of previous similar selected papers.Literature review on ecosystem-based and structural risk reduction efforts and the application of the INVEST coastal vulnerability method to assess their effectiveness was conducted to get an overview of previous research, then analyze variables were used to create the assessment model.Literature reviewed was selected from journals that could be accessed from the scientific research databases Sciencedirect, Researchgate, Google Scholar, and Sinta.Keywords used to search for related research were "Eco-DRR", "Ecosystem based disaster risk reduction", "Structural disaster risk reduction", "INVEST coastal vulnerability".The research was carried out in three phases.The initial phase commences with a comprehensive examination of existing literature.A literature review involves conducting a thorough examination and evaluation of previously selected works that are comparable in nature.A comprehensive analysis of past research was undertaken to examine the success of ecosystem-based and structural risk reduction measures.This included a literature study and the application of the INVEST coastal vulnerability approach to assess their efficacy.The evaluation model was developed based on the factors identified during the analysis.The literature evaluated was sourced from scientific research databases such as Sciencedirect, Researchgate, Google Scholar, and Sinta.The search was conducted using the following keywords: "Eco-DRR", "Ecosystem based disaster risk reduction", "Structural disaster risk reduction", and "INVEST coastal vulnerability".
The second stage involves analyzing the acquired research paper data.The research employs a qualitative comparative descriptive method for analysis.The qualitative descriptive approach involves the examination of an object, condition, mental system, or event in its current state.The data is gathered from many sources such as notes, papers, research reports, and other official documents.Comparative studies involve analyzing the presence of one or more factors in multiple study publications.The analysis was performed by scrutinizing the articles and assessing if the research encompassed an evaluation of many variables pertaining to the amalgamation of ecosystem-based and structural catastrophe risk reduction approaches.
The third phase involved creating an evaluation framework for the combined ecosystem-based and structural catastrophe risk reduction model, utilizing the INVEST coastal vulnerability approach.This model represents the primary outcome of this research and can be utilized for future investigations, such as evaluating the model's effectiveness in reducing coastal disaster risks in Sikka Flores.11 (Dissanayaka et   al., 2022)   x x x x 12 (Nehren et al.,   2017)   x x x 13 (Quitain, 2021)  x x x 14 (

Result and Discussion
By utilizing keywords in the scientific research databases Sciencedirect, Researchgate, Google Scholar, and Sinta, a total of 94 research papers were discovered.Upon further examination of these 94 articles, it was found that 18 of them either employed the INVEST coastal vulnerability approach or were pertinent to evaluating the risk of coastal disasters.An examination of the 18 publications listed in Table 1 was conducted to investigate the factors employed by the researchers.The variables are employed in the development of a hybrid assessment model for reducing catastrophe risks in coastal areas, with a focus on ecosystem-based and structural approaches.
The researchers concluded that several data variables can be utilized to construct a hybrid model for assessing tsunami risk reduction.These variables include landmass characteristics such as agriculture and forest coverage, bathymetry, climatic factors like waves and wind (including rainstorms), digital elevation models (DEM), natural habitats like Mangrove, Seagrass, and Coral reef, sea level rise, oceanography, shoreline type (including geomorphology, topography, and coastal relief), beach characteristics, sand dunes, surge potential, construction type, and artificial structures like roads, breakwaters, and seawalls.All of these characteristics were included in the study and will be combined with the population in the coastal area.
Based on the analysis of the previous articles, it was determined that the several data variables mentioned earlier can be used to evaluate the effectiveness of hybrid disaster risk reduction initiatives.The depicted research model in Figure 1 commences by transforming all variables into spatial data for analysis using GIS with the INVEST toolbox (extension).This approach is mostly employed to evaluate the vulnerability to natural disasters in coastal regions caused by hydrometeorological hazards such as large waves, storm surges, erosion, flooding, and coastal storms.The INVEST method can also be utilized to evaluate the efficacy of a hybrid approach for assessing tsunami risk.
The spatial data underwent processing using INVEST GIS to produce a coastal vulnerability model.Tabulation analysis was conducted to establish a coastal exposure index, which was then represented as vulnerability maps.The vulnerability maps generated were utilized for qualitative descriptive analysis of both methods, employing GIS spatial analysis for visual and automated assessment.
Spatial analysis examines the properties of spatial distribution and analyzes the characteristics of spatial aggregation.The distribution can be observed in the correlation between hybrid disaster risk reduction efforts and vulnerability, and the extent of this correlation, if any.The analysis also examines the distribution of aggregated regions where hybrid efforts have been implemented, as well as the presence or absence of a reduction in vulnerability.This model enhances the advancement of methodologies and tools for studying and evaluating hybrid disaster risk reduction initiatives in coastal areas.There are different approaches to disaster risk reduction, including those that solely rely on ecosystem-based methods, those that solely focus on hard structural measures, and hybrid approaches that combine both ecosystem-based and hard structural efforts.It is important to consider that studies have shown that relying solely on ecosystembased methods may not be sufficient to withstand intense disaster pressures in the long term.On the other hand, solely relying on structural measures can increase environmental vulnerability and eliminate the potential benefits of environmental services for human life and environmental preservation.

Conclusion
The likelihood of a natural calamity occurring in the coastal regions of Sikka Flores is quite high, particularly in terms of hydrometeorological hazards such as high waves, storm surges, coastal flooding, and tsunamis.Using the GIS-based INVEST method, the effectiveness of various ecosystem-based and structural disaster risk reduction efforts, including both green structural and gray structural efforts, can be evaluated.This method requires a large quantity of spatial data to generate vulnerability maps, and then descriptive analysis is performed by analyzing patterns of distribution and aggregation.The INVEST method can be used to construct a model for valuing a hybrid engineering approach of ecosystem-based and structural-based disaster risk reduction in coastal areas.This model enhances the development of methods and instruments for analyzing and evaluating hybrid coastal disaster risk reduction efforts.

Figure 4 .
Figure 4. Model for valuing hybrid ecosystem-based and structural disaster risk reduction of coastal areas.

Table 1 -
Research Data Variables of EcoDRR and Structural Model in Coastal Areas.