1. Introduction

2. Methodology

2.2. VA Framework

The concept of vulnerability, as defined in [38], refers to “the degree to which a system is susceptible to, or unable to cope with, adverse effects of climate change, including climate variability and extremes.” This definition encompasses three key components: exposure to climate hazards, sensitivity to hazards, and adaptive capacity to hazards [38]. The exposure in this study comprises Long-term and Extreme Sea Surface Temperature, Extreme and Changes in Precipitation, Sea-Level Rise, Storm Surge (specifically for mangroves), and Storm Frequency. Sensitivity criteria include Intrinsic Characteristics, Coastal Integrity, Anthropogenic Disturbances, and Habitat Characteristics. Sensitivity and exposure were considered together to assess potential impacts, following the methodology proposed by [39]. Adaptive capacity criteria consist of scores related to Governance, Human Intervention, and Habitat Morphology.

To evaluate vulnerability, the potential impact was cross-tabulated with adaptive capacity, applying this framework to each coastal resource. The preceding paragraphs will delve into the detailed framework for each coastal resource. Figure 7 visually represents the comprehensive framework employed in performing the Vulnerability Assessment (VA). This structured approach ensures a systematic evaluation of vulnerability by considering the unique characteristics and interactions of each coastal resource in response to climate hazards.

2.2.1. Exposure

The exposure data utilized in this study was derived from the research conducted by the University of the Philippines – Marine Science Institute (UP-MSI), focusing on geographic factors. This exposure layer incorporates various elements, including long-term and extreme sea-surface temperature (IOT, EHE), extreme and changes in precipitation (ER, DWB), and sea-level rise (SLR). The ratings are presented in cluster form, with the municipality of Lian, Batangas falling under cluster III. Figure 8 provides a visual representation of the exposure layer, covering the entire Philippines. As outlined in Table 3, specific ratings were assigned to each factor: IOT received a score of 2, EHE scored 4, ER obtained a score of 1, DWB was rated 5, SLR received a score of 5, resulting in an average of 3.4 for all entries under the exposure layer. Notably, DWB and SLR garnered the highest scores of 5, indicating their elevated significance in the exposure assessment, while ER received the lowest score of 1.

This exposure layer, with its distinct ratings and cluster categorization, provides a comprehensive overview of the geographic factors contributing to the vulnerability of the municipality of Lian, Batangas, and is instrumental in understanding and assessing the potential impacts of climate hazards on coastal resources in the region.

2.2.1.1. Storm Surge

The storm surge map employed in this study is derived from the Storm Surge Hazard map, specifically based on the predicted storm surge height of 5 meters (Advisory 4). This map, illustrated in Figure 9, is particularly relevant for assessing the potential impact on mangroves, given that a 5-meter storm surge can significantly affect these coastal ecosystems. The Storm Surge Hazard map was generated as part of the DOST-Project NOAH (Nationwide Operational Assessment of Hazards) program, with its main office situated at the National Institute of Geological Sciences (NIGS), University of the Philippines.

It’s crucial to note that this exposure layer was exclusively utilized for the evaluation of mangroves. This specific map provides valuable information about potential storm surge impacts, aiding in a focused and detailed assessment of the vulnerability of mangroves in the study area.

2.2.1.2. Sea Surface Temperature

The Philippines has witnessed a notable increase of 0.3 degrees Celsius in sea surface temperature [40]. Recorded sea surface temperatures spanning the period from 1985 to 2006 were consistently higher compared to other areas within the Coral Triangle in Southeast Asia [8]. Sea surface temperature is a critical factor influencing the health of biodiversity across various ecosystems. Elevated sea surface temperatures can lead to coral bleaching, a phenomenon that adversely affects fish production and yields.

Figure 10, presented below, depicts a time series of sea surface temperatures based on the study conducted by [8]. This visualization provides a chronological overview, highlighting the trends and variations in sea surface temperatures over the specified period. The observed increase in sea surface temperature underscores the significance of understanding and monitoring these changes to assess their potential impact on marine ecosystems and fisheries.

2.2.1.3. Sea – level rise

The rise in sea levels is a contributing factor to accelerated beach soil erosion, posing threats not only to communities residing in coastal areas but also to the coastal resources themselves [7]. A study [41] projecting a high emission scenario anticipates a sea-level rise of 1.0 meter by the year 2080. However, observations in the Philippines indicate a more recent increase ranging between 0.2 to 0.4 meters in sea level rise [42]. This data emphasizes the real and current impact of rising sea levels in the country, underscoring the need for proactive measures to mitigate the adverse effects on coastal communities and their valuable resources.

2.2.1.4. Storm frequency

The frequency of Category 5 typhoons passing within a 300 km-radius of each coastal site was tallied over a 30-year record and subsequently mapped by [43], as illustrated in Figure 11. This mapping provides a visual representation of the occurrence and distribution of these extremely powerful typhoons in proximity to each coastal location over the specified time frame.

2.2.2. Sensitivity

The sensitivity criteria for mangroves, seagrasses, and corals were adopted from two sources: the study by [44] titled “Development of GIS-Based Coastal Resources Vulnerability Assessment Framework for Coastal Resources in the Philippines” and the “Vulnerability Assessment Tools for Coastal Ecosystems: A Guidebook” prepared by the Marine Environment and Resources Foundation, Inc. [45].

For mangroves, the sensitivity criteria under intrinsic characteristics include proximity to coastal development, proximity to aquaculture, the condition of the beach in the last 12 months, whether the coastline is prone to erosion, width of the shore platform, and steepness of the coast. Anthropogenic disturbance criteria encompass solid waste accumulation and management, presence of tourism activities and other activities, coastal mining and/or wood harvesting/deforestation, conversion of coastal lands from rural-agricultural to residential and industrial use, and pollution such as oil spills, construction of landfills, and unregulated dumping. In habitat characteristics, sensitivity criteria involve the age of the mangrove stand, the state of the natural forest, the kind of mangrove species present, and the population density of large mangroves compared to small mangroves.

For seagrasses, anthropogenic disturbance sensitivity criteria include water quality, solid waste accumulation and management, presence of tourism and other activities, catch rates, catch composition, dependence on fishing, coastal and offshore mining, and conversion of coastal lands from rural to other uses. Intrinsic characteristics criteria involve proximity to coastal development, proximity to aquaculture, proximity to river outlets, depth of seagrass habitat, changes in the beach in the last 12 months, proneness of the coastline to erosion, width of the shoreline, width of the shore platform, and steepness of the coast. Habitat characteristics include the presence of key species, extent of seagrass cover, and composition of seagrass beds.

For corals, intrinsic characteristics sensitivity criteria include proximity to coastal development, proximity to aquaculture, proximity to river outlets, depth, changes in the beach in the past 12 months, proneness of the coastline to erosion, width of the shore platform, and coastal steepness. Anthropogenic disturbance criteria are the same as those for seagrasses. Habitat characteristics include the presence of key species, dominant growth forms, and the condition of the coastline lined by coral reefs/communities. Detailed tables presenting this data are not included in this text.

2.2.3. Adaptive Capacity

The criteria used for the indicators of Adaptive Capacity were adopted from two sources: the study by [44] titled “Development of GIS-Based Coastal Resources Vulnerability Assessment Framework for Coastal Resources in the Philippines” and the “Vulnerability Assessment Tools for Coastal Ecosystems: A Guidebook” prepared by the Marine Environment and Resources Foundation, Inc. [45].

For the governance component of adaptive capacity for mangroves, the criteria include the existence of local ordinances, community support, and local knowledge, as well as aspects related to Marine Protected Areas (MPAs), such as their existence, extent of focus, and the need for expansion. Maps of MPAs in Lian, Batangas, are illustrated in Figure 12a,b.

Under human intervention, criteria comprise habitat restoration efforts, awareness of coastal resources within communities, and the extent of coastal modifications (including pier wharf and seawall construction, reclamation, and foreshore use). In habitat morphology, criteria include the presence of refuge sites (buffer zones for community extension) and the presence of adjacent habitats (other coastal resources). This framework provides a structured approach to evaluating the adaptive capacity of mangroves, encompassing governance, human intervention, and habitat morphology. The inclusion of specific criteria enables a comprehensive assessment of the resilience and adaptive capabilities of mangrove ecosystems in the study area.

In assessing adaptive capacity for seagrasses, the governance criteria parallel those used for mangroves. Under human intervention, criteria include the dependence on fisheries’ resources, average fishing experience per fisher, effectiveness of fishery resource management plans, habitat restoration efforts, awareness of coastal resources, awareness of the importance of each coastal resource, and the extent of coastal modifications. Habitat morphology criteria for adaptive capacity of seagrasses encompass the presence of adjacent habitats, the condition of Enhalus acoroides (density composition among seagrasses), and the continuity of seagrass beds.

For corals, governance criteria mirror those used for mangroves and seagrasses. Human intervention criteria for corals align with those used for seagrasses. In terms of habitat morphology, criteria include coral cover health, the presence of massive corals compared to branching ones, the comparison of large colonies to small colonies of species, the reduction in coral diversity, and the presence of adjacent habitats (other coastal resources). This consistent framework ensures a comprehensive and comparable evaluation of the adaptive capacity of seagrasses and corals, considering governance, human intervention, and habitat morphology as integral components of their resilience.

2.2.4. Scoring and Rescaling

The Coastal Integrity Vulnerability Assessment Toolkit (CIVAT) guidelines, derived from a study conducted by the University of the Philippines - Marine Science Institute (UP-MSI), were employed to score various criteria for exposure, sensitivity, and adaptive capacity. These guidelines not only facilitated the initial scoring based on raw numerical values but also aided in the subsequent rescaling of scores into descriptive categories such as High, Medium, and Low.

A combination of criteria from Integrated Coastal Sensitivity, Exposure, and Adaptive Capacity to Climate Change (IC-SEA C) and CIVAT was utilized for the assessment of sensitivity and adaptive capacity. Additionally, storm frequency and storm surge were integrated into the exposure layer. However, for the mangrove vulnerability assessment, the team specifically utilized storm surge.

The exposure map in Figure 11 served as the basis for scoring storm frequency of Category 5 typhoons. The scores for exposure indicators were then rescaled according to the CIVAT guidelines. This structured approach ensures a comprehensive and standardized evaluation of the vulnerability of coastal resources, particularly mangroves, by considering exposure to extreme weather events.

Table 4. Exposure Scores for Storm Frequency.

Table 4. Exposure Scores for Storm Frequency.

Barangay	Score	Numerical Score
Balibago	Low	2
Binubusan	Low	2
Lumaniag	Low	2
Luyahan	Low	2
Matabungkay	Low	2
San Diego	Medium	3

Scores and rescaled values of Sensitivity criteria for mangroves, and seagrasses proximity to coastal development (Table 5 and Table 6), proximity to aquaculture areas (Table 7 and Table 8), proximity to river outlets (Table 9), and Depth criteria scores for seagrasses and corals are shown in Table 10.

The proximity of corals to Marine Protected Areas (MPAs) was assessed, and the scores were subsequently rescaled. This process involved plotting the coordinates provided by the Municipal Environment and Natural Resources Office (MENRO) in Lian, Batangas. Table 11 outlines the scoring criteria utilized for assessing the adaptive capacity of corals in proximity to MPAs. Similarly, criteria for scoring the proximity of corals to coastal development can be found in Table 12. Additionally, Table 13 provides the scoring criteria for the proximity of corals to river outlets. These structured criteria and scoring systems ensure a systematic evaluation of the adaptive capacity of corals in relation to their proximity to MPAs, coastal development, and river outlets.

The rubrics employed for identifying potential impacts and conducting the overall vulnerability assessment for each coastal resource were derived from the study conducted by [44]. The rescaling of data obtained from the Focus Group Discussion (FGD) followed the methodology outlined in the work of [45].

Following the Vulnerability Assessment (VA) framework illustrated in Figure 7, ratings for potential impacts associated with Intrinsic Characteristics, Governance, Anthropogenic Activities, and Habitat Characteristics were determined based on the sensitivity and exposure ratings [45], as depicted in Figure 13. Subsequently, Table 4, Table 5, Table 6, Table 7 and Table 8, along with other data, were rescaled using the Coastal Integrity Vulnerability Assessment Toolkit (CIVAT) guidelines, which employ descriptive ratings such as High, Medium, and Low, corresponding to the original ratings of Very High, High, Medium, Low, and Very Low. While the specific computations are not presented here, the potential impacts for each of these characteristics were calculated using the field calculator in ArcMap.

Ratings for Vulnerability of each Intrinsic Characteristics and Governance, Anthropogenic Activities, and Habitat Characteristics were based on the ratings on Potential Impact and Adaptive Capacity as shown in Figure 14.

The ratings for the Overall Vulnerability of each coastal resource were determined based on the ratings for Intrinsic and Governance, Anthropogenic, and Habitat Vulnerabilities, as outlined in [44]. The rubric for Overall Vulnerability, considering Anthropogenic Characteristics, Intrinsic Properties and Governance, and Habitat Characteristics, is illustrated in Figure 15. This rubric serves as a guideline for assessing the combined impact of these factors on the overall vulnerability of each coastal resource.

3. Results and Discussion

4. Conclusion

5. Recommendation

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