Climate Hazards Management of Historic Urban Centers: The Case of Kaštela Bay in Croatia

Abstract

The preservation and protection of historic urban centers in climate-sensitive coastal areas contributes to the promotion of culture as a driver and enabler of achieving temporal and spatial sustainability, as it is recognized that urban heritage is an integral part of the urban landscape, culture, and economy. The aim of this study was to enhance the resilience and protection of cultural heritage and historic urban centers (HUCs) in the coastal area of Kaštela, Croatia, by providing recommendations and action guidelines in response to climate change impacts, including rising temperatures, sea levels, storms, droughts, and flooding. Preserving HUCs is essential to maintain their cultural values, original structures, and appearance. Many ancient coastal Roman HUCs lie partially or entirely below mean sea level, while low-lying medieval castles, urban areas, and modern developments are increasingly at risk. Based on vulnerability assessments, targeted mitigation and adaptation measures were proposed to address HUC vulnerability sources. The Historical Urban Landscape Approach tool was used to transition and manage HUCs, linking past, present, and future hazard contexts to enable rational, comprehensive, and sustainable solutions. The effective protection of HUCs requires a deeper understanding of the evolution of urban development, climate dynamics, and the natural environments, including both tangible and intangible urban heritage elements. The “hazard-specific” vulnerability assessment framework, which incorporates hazard-relevant indicators of sensitivity and adaptive capacity, was a practical tool for risk reduction. This method relies on analyzing the historical performance and physical characteristics of the system, without necessitating additional simulations of transformation processes.

1. Introduction

There is a continuing research interest in the conservation of historic buildings, historic urban landscapes, and centers due to their contribution to culture, heritage, and heritage conservation and sustainable development. With the increasing climate change, research interest is also growing, especially in coastal urban areas, which are increasingly threatened by interconnected climate hazards from land and sea. The problem is complex because protection, preservation, and conservation must guarantee the protection of historic architecture, historic features, and landscapes in an uncertain future climate and urban environment that underlines the importance of preserving urban areas and the need for functional continuity of these areas. The sustainable relationship between ancient and modern and the development of cities and historic urban centers for the future have become important issues.

The research originated from the “Interreg Mediterranean CO-EVOLVE Management Plan for the Coastal Area of the City of Kaštela” project in Croatia, which is not otherwise detailed in this work [1]. This project served as a database and information source for the subsequent research presented herein. The aim of this study was to develop a methodology and tools for managing climate-related hazards, with a focus on strengthening the resilience and protection of cultural heritage (CH) and historic urban centers (HUCs) in the karst coastal area of the Adriatic Sea in the Dalmatia region of Croatia, using the Kaštela Bay area/city of Kaštela as a case study [2]. The research adopted a learning-by-example approach, which proved effective for acquiring new skills, understanding complex systems, and developing problem-solving strategies.

The City of Kaštela is a densely built-up area along the coast of Kaštela Bay on the eastern coast of the Adriatic Sea near the city of Split, which is under increasing climate threats from the sea (mean sea level rise and storm surges) and land (surface-water floods) (Figure 1). HUCs along the seacoast are the most at risk because they are continuously exposed to climate and human-induced hazards, such as the dynamic growth of the mean sea level, climate change, and uncontrolled urbanization. Therefore, climate change-related impacts on coastal communities, such as coastal flooding and erosion, landslides, strong winds, storm surges, pluvial flooding, droughts, heat waves, and cold spells, are becoming more frequent, with increasing negative consequences for nature, people, and CH [3]. Similar climatic and non-climatic stresses occur on other parts of the Dalmatian coast, highlighting the need to define a common framework methodology and appropriate tools and measures for hazard management that are effective for this karst coastal cultural heritage area [2]. Dalmatia is no exception; similar problems and threats to coastal CH occur throughout the Mediterranean and other regions [4,5,6]. Each coastal area has distinct features related to coastal landscape, landforms, influencing factors, natural beauty, historical significance, architecture, culture, and maritime heritage; therefore, research needs to be adapted to local characteristics. Such a tailored approach was applied in this study for the Kaštela Bay area, as detailed in this paper.

Dalmatia and the Kaštela Bay urban area have long histories [7,8]. Living in urbanized settlements began with the arrival of the Greeks (≈400 BCE) and continued with the Roman Empire, Byzantium, Venice, Napoleon, and, more recently, the Austrian Empire. These civilizations have created tangible and intangible urban heritage sites, mainly in coastal zones. The ancient Greek and Roman civilizations lasted the longest (400 BCE to 400 CE) and built cities such as Zara, Tragurion, Siculi, Salona, Spalatum, and Epetion, near which modern cities later developed. Factors such as the Mediterranean climate, karst landscape, abundance of fresh water, favorable conditions, fertile coastal land, sheltered bays, and convenient access to the interior of the continent support development and sustainable livelihoods.

External forces, including solar energy (climate), and internal forces, such as the culture and civilization of society, water culture, and civilization, shape nature and society. The historical climate periods that shaped the evolution of civilization in the area were the Roman Warm Period (300–400 CE), Late Antique Little Ice Age (536–660 CE), Medieval Warm Period (800–1250 CE), Little Ice Age (1350–1850 CE), and Modern Warm Period (from 1850 CE to the present) [9]. Warm and stable climatic periods were favorable for development and progress, whereas cold, dark, and unstable climatic periods were unfavorable. Long-term shifts in climate alter water availability, which, in turn, affects food, energy, and societal resilience. Climate change is caused by variations in solar energy, which spread to biotic and abiotic environments and eventually affect socio-political systems in the long run. During this period, the increase in mean sea level (MSL) exhibited a constant upward trend. Over the last 3000 years, the rise was very small and had a slow and minimal impact on nature and humans (≈3.0 m), as people and biota had sufficient time to adapt to the changes [10]. However, from 1880 to 2000, the growth accelerated to a rate of about 1.8 mm/year (total 20.32 cm), and for the last 15 years, the rate increased to 3.1 mm/year, to the level of growth in the Holocene period (6–9.9 mm/year) [10]. Climate variations alter the timing and magnitude of runoff and soil moisture, change groundwater and sea levels, and affect water quality. It affects the environment by causing sea level rise, storm surges, droughts, and flooding. Therefore, the greatest hazards to coastal zones over the last 30 years have been flash floods, MSL rises, and storm surges [1]. These occurrences are superimposed in a climate hazard at the point of collision or contact between the sea and freshwater. Otherwise, the most densely populated, property-rich, and economically valuable urban areas include HUC locations.

This study was conducted to advance scientific knowledge and support the formulation and implementation of policies to mitigate the adverse impacts of climate change and vulnerability in coastal areas. This study focused on assessing the impact of climate change adaptation and resilience measures on coastal CH and HUCs.

The HUCs and other forms of CH in Dalmatia encompass both tangible and intangible elements shaped by human and natural history. These assets hold significant educational, aesthetic, cultural, and social value for present and future generations, in addition to their potential economic importance [2]. Therefore, they must be adapted and strengthened in response to the impacts of climate change and socioeconomic development. The topic is complex because assessment requires a time dynamic approach, “past → present → future”, i.e., hysteresis effect. Therefore, methods that systematically integrate and explain historical, present, and future interactions between climatic, natural, and human environments and their physical, cultural, and social contexts have been applied. These include the vulnerability assessment framework proposed by the IPPC 2014 [11], driver-pressure-impact-state-response (DPSIR) framework [12], historic urban landscape-based approach (HULA) [13,14], object-based approach, and local lead adaptation (LLA) [15]. This methodology of addressing the sustainability challenges of HUCs has not yet been applied in Dalmatia. Sustainability is mainly analyzed in the context of future exposure based on climate model forecasts that are too general for local practical applications.

2. Materials and Methods

2.1. HUC of Evolution in Kaštela City

The warm Roman period was a period of urbanization and city development in the Kaštela area, whereas the Avars and enslaved people conquered and destroyed Roman cities and infrastructure in the Kaštela Bay area. In 630 CE, at the invitation of the Byzantine emperor, the eastern coast of the Adriatic Sea was settled by the Croats, who lived in the area of Kraków in present-day Poland [8]. Thus, advanced ancient civilizations and cultures were replaced by barbarians who did not build cities modeled after Rome. They lived mostly in the hinterlands, where they established their kingdom. Byzantium ruled ancient cities and ports on the coast, followed by Venice (991–1808 CE), which was constantly at war with its Slavic neighbors. The Republic of Venice rebuilt demolished ancient ports and cities and built new castles and forts along the coast. These castles marked the beginning of the emergence of settlements in their vicinity, that is, today’s HUCs of Kaštela (Figure 2). The expansion of urban areas continued under Austrian rulers (1815–1918) and has persisted to the present day [16].

The development of agriculture in the Kaštela Bay area during the late Middle Ages (1300–1500) was the primary reason for the construction of fortified manorial or country houses, referred to as “castles”. In Croatian, these are called “Kaštilac”, a term from which the name of both the bay and the city is derived [16]. The landowner resided in the castle where he stored agricultural products, whereas the peasants built their houses near the coast [7].

Castles were built on rocks in the shallow sea off the coast to make them easier to defend against land-based attackers (Turks and neighbors), as shown in Figure 2. When the danger from the Turks ended (1699), the coast near the castle gradually filled in, sometimes up to the castle walls themselves, thereby losing its original appearance and defensive functions. Thus, the castle and church nearby became recognizable landmarks of the settlement that spread along the coast and deeper into the mainland, forming the seven Communities of Kaštela. Over time, they merged to form a unique urban agglomeration known as Kaštela (Figure 1).

Because of this process of evolution, the HUCs and surrounding residential zones are today the topographically lowest areas and are therefore the most vulnerable to extreme weather events. The Kaštela coast is exposed to risks from sea level rise and flooding, extreme weather events (e.g., storms), inappropriate urbanization, and urbanization-induced biogeophysical effects, such as erosion, land collapse, severe runoff, floods, and biodiversity loss. Thus, the vulnerability and risk assessment of HUCs must include the broader urban context and geographical settings, as well as the historical evolution of nature and human impacts. The remains of ancient ports and cities are no longer visible, as they are now covered with alluvial sediment deposits transported by water from the hinterlands, whereas ancient ports are below sea level. Therefore, castles and HUCs are designed as visible urban heritage sites that are essential for preservation and protection.

2.2. Methodology

2.2.1. Conceptual Framework of Problem Evolution

Climate hazards are physical processes or events, hydrometeorological or oceanographic variables, and other phenomena that can harm human health and assets, endanger livelihoods and sustainability, and threaten natural security. Physical processes generate physical risks to humans and nature, as well as to urban physical capital, CH, and HUC. Assessing cumulative historical impacts and defining appropriate measures to strengthen resilience and adaptation are crucial to achieving HUC sustainability. The biggest challenge is the hysteresis of the system and insufficient understanding of the planning framework, including the planning period, design norms, design variables (temperature, precipitation, and windstorms), and uncertain MSL rise values during the planning period [9]. Therefore, a simplified conceptual framework for vulnerability assessment was applied that considers the historic, present, and future socioeconomic, natural, and technological aspects of the problem, delinked from uncertain exposure, as shown in Figure 3.

Coastal systems are generally defined in terms of interactions between natural and socioeconomic systems. The same applies to coastal HUCs in both natural and socioeconomic coastal systems. Therefore, the impacts and vulnerability were defined in terms of the evolution of interconnected natural, socioeconomic, and historical urban systems (Figure 3a). The hierarchy of system interconnection is as follows: the natural system has the largest scope (global/regional) and generates impacts on all other internal systems; the socioeconomic system has a regional and local scope and generates impacts on local natural and urban systems, including CH and HUC in local (micro) systems.

Hierarchy illustrates the cumulative climate and non-climate present and long-term human-induced changes and possible impacts, i.e., defining the “cultural heritage vulnerability index”, a tool used to assess the susceptibility of CH sites to various threats, encompassing both natural and anthropogenic hazards [18]. They entail causal loops that run from society to the physical/natural system (dashed arrows) and back to society (solid arrows; Figure 3a).

The overall objective is to strengthen the sustainability of the HUC in existing and future natural and socioeconomic environments, as “heritage conservation and preservation can lead to higher property values and increase tax revenues, more jobs, neighborhood revitalization, and economic growth. It offers an appreciation of history and allows us to understand how people lived in the past, symbolizing their predecessors and neighbors today as well as the world they occupy” [19]. The “cultural heritage vulnerability index” links the poorly known past, through the known present, to strengthen resilience for an uncertain future. This demanding assessment requires the application of a locally adapted DPSIR framework.

2.2.2. Framing of Sustainability Issues

Natural factors and human-induced changes, such as the release of greenhouse gases and alterations in land cover, have a permanent impact on climate through changes in surface energy and moisture budgets. The change in biogeophysical effects impacts the nature and socioeconomic system, depending on the exposure, system sensitivity, and autonomous and implemented planned adaptive capacity (PAC) to change, both from sea level rise and related climate change. Simultaneously, human activities (such as land use, land degradation, urbanization, and pollution) occur, and human-induced non-climate stresses reduce natural autonomous processes and ecosystem capacity. This was the case in the past, is the case today, and will continue to be the case in the future.

Socioeconomic and natural changes generate historic cumulative impacts on HUC depending on exposure (E), sensitivity (S), and adaptive capacity (AC). This clearly shows that the problem should be viewed systematically and comprehensively, respecting the hierarchy of systems, dynamics of internal and external processes, and the input-output processes of energy, water, and matter. Therefore, successful problem solving requires an integrated assessment approach and methodology for cumulative impact analysis, as well as integrated planned adaptation measures for both natural and socioeconomic systems and HUCs. In this context, the process of historic cumulative vulnerability assessment has become part of a broader framework for analyzing far-reaching environmental and socioeconomic transformations and restoration.

Vulnerability of historic buildings/castle and HUC, and an uncertainty regarding the magnitude of climate changes in the planning period require that the problem be analyzed dynamically, assessing hazard-relevant indicators from the historic period of construction of fortified manorial/country buildings—“castle” up to the present time, and then further to the uncertain future (see Figure 2). Studying historical trends and assessing the dynamics of change of S and AC indicators, it is possible to gain insight into the present state of vulnerability and plan for the future. This approach simplifies problem-solving because vulnerability is viewed as an internal property of the system (heritage, HUC), delinked from uncertain future exposure to hazards, as potential stresses and impacts are difficult to assess. Therefore, it is simpler and more reliable to determine the vulnerability (V) based on the internal properties of the system instead of the interaction with future exposure, S, and AC, as shown in Figure 3 [11].

V = f(S, AC)

(1)

A prerequisite for gaining insight into the trend of changes in vulnerability and the state of the system is that the assessment period encompasses the entire historical evolution of the HUC, that is, hysteresis, in which a system’s output depends on both present and past inputs. This involved assessing the specificity of the vulnerability, CH, HUC, and risk management. The assessment included many historical unknowns, such as socioeconomic, natural, cultural, and acting factors. Therefore, the process must focus on the dominant hazards relevant to the vulnerability index assessment.

2.2.3. Dynamic Vulnerability Assessment Framework

The methodology for the historical climate change vulnerability assessment of HUCs was based on the DPSIR framework [12]. It is an integrated assessment framework that simplifies the representation of complex physical and social systems by focusing on the interactions among the environment, heritage, society, and economy. The scoping procedure assessed the past and present impacts of global and regional socioeconomic and biogeophysical factors, local hazard-specific sensitivity, and AC indicators related to pressure (P), state (S), impact (I), and response (R), as shown in Figure 4. The DPSIR framework is internally bound to the pressure and response within the system boundary and externally bound to cross-border global impacts (such as climate change) based on historical data and existing trends of change, because both systems are open systems that exchange energy, water, and matter. External and internal drivers continuously affect the biogeophysics, biogeochemistry, and biogeography of the coastal environment (energy and matter flow, hydrological cycle, carbon cycle, and vegetation dynamics), modify the environment, generate natural and manufactured pressures, and change the state of socioeconomic activities and the natural environment. Changes disrupt environmental safety and livelihood sustainability, and pose a threat to environmental livelihood security, which is essentially sustainable.

A systematic solution implies that the DPSIR framework at each time sequence considers the drivers, pressure, state, impacts, and responses related to the socioeconomic and natural-physical framework by applying relevant indicators, whether estimated values or expert opinions/judgments.

Similarly, the purpose and size of a building, choice of location, type of construction, and other socioeconomic factors all contribute to determining the characteristics of historic urban areas. They define the cultural-historical significance and value of a locality. The time sequence of socioeconomic changes transforms the initial state into the present state, thereby altering the value of the urban space or locality. Tangible CH and natural heritage should be preserved and rehabilitated through adaptation and resilience measures to restore the historic landscape and appearance as faithfully as possible.

More time-relevant DPSIRs should be assessed to evaluate the problem dynamically, including the period when the castle was built, the current state of the HUC in which the changes were expressed, and the expected climate-induced future environments. This is how the historical context of the hazard evolution and hazard-induced vulnerability of the HUC was obtained. As a result, valuable insights can be gained into the sequence of causes of vulnerability and the validity of the response measures used in the past. Past experiences have provided guidelines for strengthening current and future resilience. All measures to strengthen resilience that were effective in the past should be respected, improved, and adapted to existing and future environments. This approach minimizes the errors in the selection and implementation of adaptation and resilience-strengthening measures for a particular HUC. It aims to determine why the measures and project parameters applied in the past were good or insufficient in the protection of the castle and HUC, and to assess whether historic adaptation and resilience measures are possible solutions for the future, and to what extent.

3. Results and Discussion

This section presents the application of the methodology and results. The assessed information serves as the starting point and guidelines for future research to plan and implement adaptation measures and strengthen HUC resistance.

3.1. Drivers, Pressure, and State

3.1.1. Natural Drivers and Pressures

Regional climate models for Croatia predict a decrease in annual precipitation, an increase in temperature, snow, rainfall volatility, and more frequent extreme climate events [20]. Changes should be relatively small until 2040, but will increase thereafter. For the period 2040–2100, models forecast an increase in average annual temperature of 0.6 to 4.0 °C and summer temperature of 0.9 to 4.7 °C, Annual precipitation is projected to decrease by 2 to 7%, with the most significant reduction in summer (5 to 25%), followed by autumn (3 to 13%) and spring (3 to 8%). In contrast, precipitation is expected to increase by about 2 to 7% in winter [20]. The MSL will rise (9–114 cm), and the winds, waves, and wave surges will become stronger and more frequent. Thus, during cyclone weather, climatic water hazards from land and sea are combined and superimposed on the coastal zone (at the shoreline). The magnitude of changes in climatic variables and the frequency of extremes are insufficiently known and subject to change because the application of mitigation measures is uncertain. However, long-term trends in climate change indicate sustained increases in global temperatures and alterations in weather patterns. However, this does not prevent us from studying these problems or designing response measures.

The karst coastal landscapes of Kaštela and Dalmatia, characterized by steep hillsides, are undergoing increasing urbanization, which increases the geopotential energy of surface water. This environment is highly sensitive to precipitation and is prone to flooding. Water, energy, and erosion processes shape the landscape and coastline morphology. Sea-level rise and fluvial sediment supply by water define the equilibrium state of shoreline hydromorphology. Until 1850, the increase in MSL was small, whereas the sediment supply was significant because of deforestation and seaward shoreline progradation, as shown in Figure 5 and Figure 6, respectively. In recent years, urbanization has significantly altered natural hydrological cycles, primarily by increasing impervious surfaces and disrupting natural drainage patterns, thereby reducing the sediment supply. Simultaneously, MSL increases, causing shoreline transgression and flood hazards. Therefore, new higher coasts have been built, resulting in greater sea depths off the coast, which induce larger waves and storm surges. Thus, new coasts are becoming increasingly vulnerable to erosion and flood hazards, including storm surges. Therefore, internal historical land-use changes, external modern-period climate changes, and MSL rise create hazards that reduce coastal zone sustainability, thereby increasing the entropy of natural and societal systems [21]. The cumulative effects of both drivers could be detected and recognized through the historical evolution of coastal changes, particularly in the HUC coastal zone. Understanding historical processes of change makes it easier to address future issues.

It follows that HUCs and old castles located in front of or on the coast, as well as tourist facilities and infrastructure along the coast, are the most at risk [1]. Based on the analysis and consultation with stakeholders, directly and through the organization of workshops, problems were determined by topics and priorities of importance, as follows:

• Flooding of low banks;
• Coastal erosion;
• Droughts, fires, heat waves;
• Increase in sea temperature and salinity;
• Changes in the natural environment and the impact on agriculture, tourism, and the economy.

Similar processes occurred in the late Middle Ages when HUCs began to form (13th–16th centuries), with the MSL 30–60 cm lower than today [10]. The climate is colder than today, but not significantly, so climate hazards and processes are similar: coastal erosion, inundation, and disruptions to coastal ecosystems [9]. Rising sea levels, changes in wave patterns, and increased storm intensities are the major factors driving these changes. These impacts can lead to damage to coastal infrastructure, displacement of communities, and the loss of valuable coastal habitats. Coastal settlements are surrounded by defensive walls and ditches/moats around the city. Thus, inland waters did not threaten old towns or structures, whereas the castle located in the sea in front of the coast was exposed only to seawater impacts and hazards, as shown in Figure 2. Because castles are located in very shallow water, storm surges do not pose a significant threat to them because the waves are affected by the ocean bottom, decreasing the wave speed, breaking waves, and creating surf in shallow water. Furthermore, as the MSL decreased, the level of coastal groundwater (freshwater floating in the sea) also decreased. Therefore, surface water hazards from land and seawater storm surge effects did not increase because the applied concepts of construction and urbanization did not connect them physically and hydrologically, except in relation to underground water floating at the top of denser saltwater. This suggests that one possible solution to mitigate future climate threats is the historic construction concept of historic urban landscape restoration [11,22]. This approach strengthened the resistance and, at the same time, restored the historical landscape of the castle.

3.1.2. Socioeconomic Drivers and Pressures

The biggest socioeconomic threat to the natural environment and sustainability is the uncontrolled urbanization that occurred after World War II, resulting in completely urbanized areas, as shown in Figure 1 and Figure 6. Therefore, there are numerous internal pressures on the environment that threaten biodiversity, quality of life, the development of sustainable forms of tourism, the most important economic branch, and the sustainability of HUCs. The coast is a culturally and economically valuable zone of a city that, by filling and expanding into the sea, threatens the historical identity of the city and increases the CH hazard, that is, the loss of value to heritage assets.

This problem is not new, as the development of castles and settlements has been marked by systematic coastal filling over previous centuries, but to a much lesser extent than in the modern period. The filling began around the castle and eventually spread along the coast, as shown in Figure 6.

These activities intensified after World War II, most notably in the last 30 years, during which tourism and coastal housing became pronounced socioeconomic trends, as shown in Figure 1 and Figure 6. Consequently, the total length of the seacoast is 23.4 km, of which 51% is completely built-up and only 16% is unchanged and natural [1]. Therefore, coastal areas are considered high-risk areas.

3.2. Historical Urban Centers

3.2.1. State, Sensitivity, and AC

Along the coastal belt, there are seven major historical urban centers and eleven castles with different heritage contents, as well as numerous archaeological vestiges, historical buildings, vernacular architecture, and historical gardens, spanning from various historic periods to the present day. The land/terrain elevation of the HUC area is mainly lower than +1.0 m a.m.s.l., whereas the basement/floor elevation point in castles is between +0.5 m and +1.1 m a.m.s.l. [1]. Therefore, AC is low, whereas sensitivity to MSL increases, and thus, vulnerability and flood risk. Adaptability is limited by cultural and archaeological constraints in the landscape, such as structural modifications and adaptations. Most castles were built in the 13th and 15th centuries, whereas the surrounding buildings were built and expanded continuously, including urban infrastructure (e.g., ports, water supply, sewage, roads), which reduced the resilience and increased the vulnerability of the HUCs castles; other structures within the HUCs survived because of conversion and use, mainly as residential objects. Therefore, in addition to adapting to climate change, renovation activities should be conducted because the HUC is protected as a cultural asset.

Ancient urban centers, which were built mainly from 50 BCE to 200 CE, and are located far from the coast, are today located below the alluvial coastal plain (2–4 m) created by the water deposition of sediment from the highland, and those that were on the coast are today below MSL, which has risen by about +1.2 m in the last 2000 years [23].

Based on the cultural value of urban space, buildings, and regulations, two basic states of cumulative vulnerability and risk are defined, (A) HUCs with high cultural and historical values threatened by internal and external forces and (B) HUCs of a more recent construction date on higher ground and thus less exposed to climate hazards, as shown in Figure 7.

The problem of vulnerability assessment has not been sufficiently explored because broader historical landscape data are missing. Old Venetian maps, which are imprecise in terms of the coastline position and elevation, are also available. More precise historic maps are military surveys of Austria and Hungary (1806–1869) [24]. Archaeological data for individual locations were also considered.

It follows that the level of coastal terrain in relation to the MSL is a dominant cumulative hazard indicator of vulnerability. At the time of construction (13th and 15th centuries), MSL was lower by about 30–60 cm, so it follows that the builders considered it acceptable to build a basement (lower ground) floor at a minimum of 1.2 m above MSL, which is a practice that has been used in modern times.

In the future, the same minimum criterion should be applied to future MSL. However, the forecasted growth of MSL for 2100 is imprecise, ranging from 9 to 114 cm, depending on the model used. Therefore, the safety factor should be viewed more broadly, considering historical trends, the local socioeconomic framework (i.e., the affordability of the level of protection), and the feasibility of implementing adaptive measures. A flexible step-by-step increase in the safety coefficient is a rational solution.

3.2.2. Response, Adaptation, and Resilience Design

In response to existing and future climate threats, communities need to plan and implement adaptation and resilience measures, both material and nonmaterial, considering the autonomous or natural AC of the environment, including biotic and abiotic factors. Both autonomous and planned approaches must be appropriately integrated to produce the most effective reduction in vulnerability, that is, entropy. The core of this protection and adaptation strategy is a landscape-based approach (LBA), which integrates a wide and historic environment into the system. This is a landmark urban landscape-based approach (HULA) [22]. Wider integration enhances the resilience of the HUC, which reduces the disorder or entropy of the system. That is why the protection and adaptation of CH assets to the present and future environment, that is “cultural heritage management”, is much more than the restoration or conservation of monuments.

Climate and socioeconomic pressures lead to changes in the state of the CH system and, consequently, affect the welfare of people and communities, both locally and regionally. Efforts to modify the impacts produce feedback effects within driver/pressure systems, that is, responses to drivers, pressure, vulnerabilities, and other effects (dashed line in Figure 4). In contrast, efforts to moderate potential damage reduce the negative impact on heritage security and sustainability. Climate adaptation solutions and actions should make heritage sites less vulnerable to current and future climate change impacts. They should also address socioeconomically induced direct and indirect pressures, such as land use, coastal land reclamation, and tourism.

The traditional “object-based approach” focuses not only on the conservation but also on adaptation and resilience of the tangible dimension of CH assets, e.g., structures, building materials, building ensembles, and facades [15]. It should help preserve sites and buildings in present and uncertain future environments, including those affected by climate-induced biogeophysical effects and impacts such as floods, storm surges, and erosion. Thus, tangible settings and contexts also encompass intangibles, settings, and contexts, and urban and sustainable development, accompanied by a greater consideration of the social and economic functions of the city and environment. This approach emphasizes the importance of balancing the benefits of socioeconomic and urban development with the preservation of CH in a climate-uncertain future. When considering the impacts of climate change, we distinguished between (i) climate transition management, which involves adaptation and resilience building by conservation, and (ii) future management, which involves integration and co-evaluation in a new (future) natural, socioeconomic, and cultural environment/framework. Heritage sites in urban contexts are assumed to compress management objects and processes. Therefore, the management of such heritage sites should cover objects (castles, other heritage structures, and monuments), natural processes (biogeophysical), and human effects (socioeconomic processes).

The main steps in implementing the HUL approach are as follows:

• Survey and mapping of the city’s natural, cultural, and human resources, and the level of integration of heritage into a wider urban and natural development framework.
• Reaching consensus by stakeholder consultations through participatory planning of values and attributes, and conveying those values.
• Assess heritage vulnerability to socioeconomic pressures and impacts of climate change.
• Integrating the outcomes into a wider framework of city development as a whole and at the local level.
• Prioritize actions for conservation and development in which the site is placed in historic and future environmental, economic, social, and cultural (urban) contexts, including water culture and civilization.
• Identification of projects, activities, and appropriate local management frameworks to ensure robust, dynamic, and well-managed CH-protected areas.

This study focuses on the LLA of CH sites and objects, considering regional and local factors such as biogeophysical, oceanographic, hydrological, geographic, economic, social, and political factors. It includes local actors and community input in shaping decisions over vulnerability and risk assessment, identification of adaptation options, prioritization of actions, and when and where to adapt [13,15].

Responses to climate drivers are also part of global actions to mitigate climate problems, which involve locally reducing carbon dioxide emissions and stopping the growth of climate change. This includes all relevant measures and activities resulting from the EU Green Deal strategy, and relevant action plans implemented at the local level. All locally pertinent measures and activities are proposed for this project. Therefore, the renewal of the coastal historic landscape is essentially a “green measure” as well.

3.2.3. Risk Assessment and Reduction

Vulnerability and risk are viewed integrally in relation to the coastal area, or rather, the wider area, including Kaštela Bay, and within the Adriatic Sea coastal hinterland natural environment, because these are open systems that exchange energy, water, and matter for sustainability. Given that coastal flooding is the greatest climate threat, the size and altitude of the coastal land were first used to determine the potential level of threat and risk. A simple rule applies: the lower the altitude, the higher the risk, which is sufficient under steady-state conditions. However, for dynamic (storm surge) conditions, sea bottom depth and storm surge processes should also be considered.

This applies equally to both internally and externally driven hazards. The internal dynamics stem from the fact that low terrain (geopotential energy) serves as a natural accumulation zone for water, energy, and matter of all drivers of pressure located on higher terrain, both physical and socioeconomic, because everything moves toward the coast because of the action of gravity.

External pressure is the Sun’s energy and the consequence of warming of the air and sea, which causes an increase in the MSL, which is addressed with mitigation measures. Internal sensitivity/vulnerability can be locally changed/managed by planning measures of adaptation, that is, changes in urban topography, for example, by raising the level of the terrain and redirecting the flow of water, matter, energy, and people. In the case of external sensitivity, the problem is more complex because it is a global process in which messages have little influence. However, even in this case, a series of adaptation measures (both material and nonmaterial) can reduce vulnerability. Autonomous adaptation (green measures) contributes to reducing vulnerability if natural processes can be restored, such as on coasts and hinterlands, through the renaturalization and restoration of biocenosis [25].

The current coastal area was classified into three threat/risk zones, Figure 8: Zone 1, up to 1 m (red); Zone 2, 1–2 m (orange); and Zone 3, 2–3 m (yellow). As the problem has been viewed dynamically across the historic period, today, and in the future, it is clear that the current terrain is the result of the evolution of the coastal area and MSL. During the period when the HUC was established (13th century), the terrain was 0.5 to 1 m lower than it is today, and the MSL was approximately 60 cm [23]. This implies that the sea covers most of the present coastline (Figure 6). In the future, for example, by 2100, the terrain is expected to change mainly because of human intervention, whereas the MSL is projected to increase by 9–114 cm. It follows that the current coast, up to 1 m high, will be threatened; therefore, the map (Figure 8) depicts the flood hazard trends—past, present, and future. The sea will cover the red zone if the coast does not rise, and the red–brown, brown–yellow, and yellow zones will spread deeper into the coastal area. The future brings us back to the geomorphological processes that occurred during antiquity. The CH from the Middle Ages slides toward the fate of the ancient CH. A distant future is inevitable if the growth of the MSL does not stop, meaning that cooling and the formation of glaciers do not occur, resulting in a new ice age.

To assess vulnerability and risk, a more precise overview of the vulnerability of coastal settlements and facilities was provided, along with a more detailed cartographic representation of the zones, including HUCs and castles, and a representation of the floor plans of buildings and house numbers for easier recording of the purpose of the facility.

Vulnerability was then analyzed using eight input data layers representing different exposure values, which were analyzed using GIS tools and presented both graphically and numerically, including street axes (km) and sewage pumping stations (number [no]). Individual immovable CH object (n) City historical zones (zones A and B) (ha), building floor plans (m²), house numbers (representing residential units), planned land use, and type of coast (type). The situation in the HUCs is presented separately and analyzed. The analysis used two sets of data related to historical and architectural heritage, both obtained from the general urban plan at a scale of 1:10,000. It was repositioned using an orthophotomap at a scale of 1:5000. The first dataset consists of polygons representing the city’s historical zones A and B. Zones A and B occupy a total area of 55 ha, and the analysis showed that 12 ha are located in the flood risk zone at 1 m a.m.s.l., which is 22%.

The vulnerability of structures in category A of the HUC was investigated in more detail. It was defined as a function of the sensitivity of a structure to changes in climate (the degree to which a system will respond to a given change in climate) and adaptation capacity (the degree to which adjustments in practices, processes, or structures can reduce exposure or sensitivity). Data were collected through fieldwork from 782 households, representing approximately 70% of the total households. The resulting database is the basis for analyzing the responses to the identified levels of threats and risks.

Resilience-strengthening measures will be planned in stages as part of a comprehensive, long-term strategy aligned with the identified protection priorities and available financial and other resources. A brief description of suitable measures and responses to threats to individual castles and the HUC is provided below.

4. Proposed Response Measures

The protection of CH from the harmful effects of water and the sea is the responsibility of state, regional, and local institutions; therefore, joint work needs to be organized to achieve the best effects at all levels and areas of jurisdiction. Without this, it would be impossible to develop sustainable protection systems and strengthen the HUCs and their structures.

Therefore, the drainage of stormwater from the coastal hinterland is integrated with the drainage of water from the city area and the rise of the MSL and underground water in contact with seawater, which together form a local hydrological system. Precipitation, land use, topographic features, and basin size were the main indicators used to assess the vulnerability and AC. Special attention should be paid to the discharges into the sea located in the lowest zones of the city’s terrain to analyze the impact of rising MSL, coastal underground waters, and the resulting inundation of the sea on the mouths of the canals and the surrounding area (bottleneck effects) to prevent water from the drainage system from spilling into the terrain where the CH and HUCs are located in the coastal zone.

Urbanization and the situation in wider areas have changed the climate, hydrological cycle, and biogeophysical processes, thereby endangering the environment and humans. Therefore, planning the use of a wider space is crucial for strengthening the sustainability of the environment and people. The proposed adaptation of coastal areas as a whole to climate change and the strengthening of protection measures are based on a green strategy that integrates changes to drivers, pressures, and states, thereby reducing negative impacts. The resilience of the environment and heritage should be strengthened to increase the capacity or ability to cope with shocks and recover from their impacts in a timely and efficient manner. This is achieved through the capture and storage of water, energy, and matter by green infrastructure, which is also suitable for gray infrastructure, such as reservoirs. The priority is to preserve the natural environment, thereby reducing land consumption through “gray urbanization”. Accordingly, the following general guidelines for spatial planning have been proposed for coastal zones:

Preservation of the cultural landscape: views of the coast and historical cores (measures to protect the coast without filling, protective greenery for other objects, zones, conservation, and integration).

Nature conservation (limited and controlled filling of the sea, revitalization of streams, and natural water flow toward the sea).

Implementation of locally sustainable flood-protection measures.

Use of green infrastructure (e.g., public greenery, streams, street green retention).

Application of green construction (to existing and new urban areas farther from the coast).

As shown in Figure 9, the HUC was analyzed and integrated with a wider coastal area using specific adaptation and resilience-building measures.

It is crucial to strengthen the sustainability of living under the current and future climatic conditions. Therefore, promoting sustainable construction is a basic measure for all new construction projects, as well as for the adaptation and adjustment of existing urban areas and facilities. In the zone of new urbanization on coastal slopes, characterized predominantly by agricultural terrain, CH objects and sites require protection and adaptation. The primary climate threats in this area are surface-water flooding, soil erosion, and fires. The HUL approach is used for these locations. The aim was to reduce the amount and velocity of water from hinterland areas, as well as the processes of erosion, slope collapse, and landslides.

The adaptation and strengthening of the resilience of CH and HUC are planned based on the same principles, but with an emphasis on conserving objects and urban areas, as well as controlling degradation processes. The emphasis is on innovation, integration, and co-evolution. Therefore, emphasis is placed on the application of effective historical solutions to adapt and strengthen resilience in the construction of structures and HUCs. The goal is to restore the environment that existed at the time of CH construction, if possible, and protect structures and urban areas from future stress, as follows:

• All castles that were once built in the sea and separated from the coast (Figure 1 and Figure 2), that is, connected to the coast with a bridge, should be reconstructed and separated from the land to the greatest extent possible, for example, by building a canal. This eliminates all flood threats caused by water coming from the land in the direction of the sea. Internal precipitation and rainwater must be collected and pumped into the sea. The infiltration of high seas into the castle interior was prevented by building a perimeter waterproof membrane/barrier and injecting a waterproof mixture into the terrain under the castle to the extent necessary. The resulting water is collected and pumped into the sea. Reduce storm surges by subsurface and surface breakwaters and by creating a shallow sea around the castle, as in the past (Figure 10). Local materials from the past were used in the construction of castles and protective structures.
• Reconstructing defensive walls and excavations around coastal areas and HUCs to prevent the inflow of land surface water into the HUCs area, thereby preventing flooding. These measures should respect heritage conservation principles, particularly the concepts of authenticity and integrity, as outlined in the ICOMOS and UNESCO charters. Collect internal precipitation/rainwater from urban areas and transport or pump it into the sea. The ingress of high seas into the interior of the coast can be prevented by building higher coastal walls and injecting a waterproof mixture into the terrain along the coast and/or under critical/low-lying areas of the city to the extent necessary. Reduce storm surges with subsurface and/or surface breakwaters to reconstruct the historical features of coastal regions.

The same is true for CHs located further from seacoasts, with priority given to locally induced hazard stresses that affect heritage sustainability. It is best to reconstruct the historical landscapes and adaptation measures used in historical engineering practices.

Where it is necessary, apply classic engineering measures: raise the entire space by 30–60 cm, build a coastal wall up to a height of 1.2 m a.m.s.l., and in front of the coast, build subsurface breakwaters. Several measures should be combined depending on the local situation, the possibilities of reconstructing the historic urban landscape, and the required level of protection. In relation to the impact of the sea, standard measures include raising the coast, building a coastal wall, an external breakwater, a breakwater, a possible embankment, creating new beaches, a shallow sea that reduces the power of waves, and other measures to reduce the impact of waves [25]. This has reduced flooding and coastal erosion. Measures related to the threat of inland water include the construction of surface-water drainage channels, application of green infrastructure, and retention of water in the basin [26]. Each HUC was addressed individually after a detailed record of the existing situation was obtained.

The relocation of historic buildings or castles to higher ground or elevations was also considered; however, it was concluded that this measure was unaffordable. Therefore, the elevation increase of coastal wall, walkways, and terrain by 0.5–1.0 m in combination with conservation of structure measures is an acceptable option for the period up to 2100. Under favorable local conditions, the elevation increase also applies to the basement floor, not the structure as a whole, so that the main structure’s characteristics and historic aspects do not change. A smaller increase in the height of the terrain and floors in buildings for a size of +0.5 m is from an engineering point of view, simple and relatively inexpensive to implement in the lowest part or the entire space of the historic urban area, while not endangering the characteristics and value of the main landmark elements.

Relocation to higher ground, conservation of objects, and reconstruction of original coastlines—That is, historic coastal morphology—Are the ultimate goals of conservation measures. However, reconstructing coastlines from the past along with the structural environment, such as that from the 15th century, is generally very difficult to achieve, except in some coastal locations that have not undergone significant modifications.

Each cattle, heritage object, and historic urban area presents a unique challenge that must be addressed individually by applying locally sustainable adaptation measures and strengthening resilience. “Returning to the past” increases the importance and cultural contribution of historic areas and CH structures to society and the tourist economy; thus, the benefits of such an approach are easily recognizable.

All conservation activities and actions should be conducted in accordance with the rules of the profession, under the supervision of relevant institutions. The aforementioned works fall within the domain of standard conservation works but also partly within the domain of engineering works and should not be a contractor’s problem. However, administrative procedures and construction costs are challenging.

The analysis of all the castles and HUCs determined that no facility built after the 13th century could be adapted and strengthened for forecasting climatic conditions and climate-induced biogeophysical processes until 2100. All ancient coastal sites, ports, and structures are below sea level, where they should remain in the future, be properly conserved, and be included in cultural and economic development. The site should be protected from anthropogenic influences such as bank filling and construction.

The lowest historical buildings are Kaštel Cippico: elevation 35 cm a.m.s.l., and Kaštilac Gomilica: elevation 60 cm a.m.s.l., historic area southern part of Kaštel Sućurac: elevation 60 cm a.m.s.l. The protection priorities were clearly defined in a simplified manner. However, the problem is much more complex, and the priority is determined by the activities carried out in the coastal zone. It is always appropriate to conduct CH adaptation as part of the ongoing adaptation activities initiated for economic interests. Currently, this process is primarily performed. Therefore, common and sustainable interests must be established in the economy and society.

Underwater archaeological sites are also present in the historic coastal areas of Dalmatia. Underwater archaeological sites are a specific type of CH that must be protected and adapted to the new climatic conditions. This topic was not the subject of this research because the state, in the exercise of its sovereignty, has the exclusive right to regulate and authorize activities directed at underwater CH sites in its waters. Those located in the HUCs must be integrated into comprehensive protection. Underwater archaeological sites are protected through a combination of international conventions, national laws, and practical measures aimed at preserving submerged CH [4]. Climate change should not alter the current situation, except that the depth of the sea will increase; thus, the impact of the wave force will decrease. Through specific conservation efforts, the site should be explored, protected from devastation, exhibited, and integrated into educational programs and introductions to the CH of cities, as well as tourism development. Legal frameworks and practical measures can help safeguard these sites for research and future generations.

5. Conclusions

Climate change stressors introduce or exacerbate diverse risks that affect the future of Kaštela Bay’s coastal natural environment, community, and CH sites. A similar conclusion can be drawn for other historic urban coastal areas in Dalmatia and other Mediterranean areas.

This study showed that the adaptation and protection of urban CH and objects in coastal areas is demanding and complex because all climate and socioeconomic stressors come to the fore, and the available data are limited. However, the climate agenda for CH management relies on an all-inclusive approach that embraces transition and change, and fully assesses Kaštela’s natural, artistic, and human resources. To adapt, protect, and achieve long-term sustainability of heritage sites, a broader perspective on the current and future needs of socioeconomic and urban management is proposed, namely, integrating heritage, planning, and development. The goal is to incorporate historical data and knowledge into future applications, which is often overlooked. The best results can be achieved by reconstructing the historic heritage landscape with a balanced application of historical and standard adaptation measures and by strengthening resilience. Each locality has unique characteristics, sensitivities, and adaptation capacities; therefore, no one-size-fits-all solution exists. The results indicate that the historical ontology of HUC systems is the best and fastest path for strengthening sustainability, rather than numerical modeling using unreliable information about future pressures.

This integrated approach requires participatory planning and stakeholder consultation at all relevant administrative and decision-making levels and specialties. Anyone should participate in deciding adaptation, resilience, and conservation aims and actions. There is a need to integrate CH values and vulnerability statuses into other natural, socioeconomic, and cultural frameworks for regional and local development. The DPSIR causal framework, which is used to describe the interaction between climate change and landscapes, and the relationship between landscapes and objects based on their historical evolution of relationships, is a suitable approach for the long-term, sustainable integration of CH into local natural and socioeconomic systems. This framework indicates that response measures must be applied equally to all process components (D-P-S-I) if long-term security is to be strengthened and to rationalize the protection of HUCs.

Historical evolution assessment of the CH and landscape is key to sustainable adaptation and resilience design. Therefore, the assessment of the vulnerability of HUC to current socioeconomic processes and the future impact of climate change needs to be simplified, considering mostly hazard-relevant indicators (cumulative impacts). This requires that the problem be solved in stages, from general assessment to more detailed and locally specific frameworks. This new approach has been applied in research on vulnerability delinked from hazards. This simplifies and rationalizes the entire integrated process and coordinates various specific activities with different issues and actors. This also helps prioritize policies and actions for adaptation, conservation, and development (i.e., good governance and management).

The DPSIR framework helps to break down the complex challenges of climate change into the relevant management sequences of D-P-S-I-R. It integrates environmental management challenges, urban area management, and HUCs into a single long-term strategy. By applying a historic LBA, it is possible to preserve and integrate HUC landscapes and structures into the future climate and socioeconomic environment, considering the relevant DPSIR indicators to support policy and decision-making. The applied approach saves time and money and enables the phased implementation of protection measures based on available data and information.

The approaches, tools, and measures used in this study could be useful for other researchers and localities with appropriate adaptations.