## 4 Hazards Analysis
### Multi-Hazard Assessment  
Studies on multi-hazard assessment report challenges related to the integration of diverse hazard types [45; 46; 47; 48; 49; 50; 51]. A major difficulty lies in combining hazards that differ in nature, measurement units, spatial and temporal scales, and intensity expression. The literature also reflects the lack of a unified methodological framework, with various definitions and analytical approaches used across studies. Three main methods for assessing hazard intensity are commonly identified: (1) hazard matrices, using color-coded classification schemes; (2) hazard indices, which aggregate multiple indicators into a single score; and (3) hazard curves, presenting exceedance probabilities for a given intensity over a defined time period. Despite these structured approaches, authors emphasize the difficulties in applying them, largely due to the limited availability of consistent and reliable hazard data.  
Considering these challenges and the available data and scope of this study, we adopted a simplified and transparent approach by calculating the arithmetic mean of the standardized hazard values (flood, landslide, wildfire, and desertification) at each location. This method aligns with internationally recognized practices for constructing composite indices, as outlined by the OECD (2008) [24], which identifies linear aggregation of normalized indicators--such as the arithmetic mean--as a widely accepted and interpretable technique, particularly when there is no clear basis for differential weighting. Although this approach does not account for potential interactions or cascading effects between hazards,it provides a practical means for generating a first-level synthesis of cumulative hazard intensity across the study area.  
The resulting Multi-Hazard Map (Figure 19) illustrates the spatial distribution of cumulative hazard intensity across Lefkas Island. According to the analysis, the Medium and high-hazard categories dominate, covering more than 63% of the island's area. These zones are primarily concentrated in the central and southern regions, where terrain complexity, vegetation, and land-use patterns increase susceptibility to multiple geohazards. In contrast, low- and very-low-hazard areas account for 14.7% and 12.8%, respectively, while very-high-hazard zones cover only 9.1% of the island.  
The analysis also reveals a clear spatial relationship between hazard intensity and settlement distribution. A considerable number of settlements fall within the medium- to high-hazard zones, highlighting their increased exposure to overlapping risks. This pattern underscores the importance of integrating hazard data into land-use planning, infrastructure development, and emergency preparedness efforts. The map provides a valuable foundation for regional risk management and can support both local authorities and civil protection agencies in prioritizing actions and raising public awareness.  
Figure 18: Desertification Hazard Map of Lefkas Island. The main map (**e**) presents the ESAI classification, while the smaller inset maps (**a–d**) depict the spatial distribution of the contributing indices (SQI, CQI, VQI, and MQI). The ESAI assessment reveals that a significant portion of the island—approximately 34.5%—is already degraded, falling into the critical (C1, C2, and C3) categories, primarily in the southern and eastern regions. Nearly 52.3% of the island is classified as sensitive (F1, F2, and F3), indicating areas highly susceptible to further degradation if current land management practices continue. Only a small area (0.6%) is identified as Not Threatened (N), reflecting limited zones of ecological stability. Additionally, Artificial Areas, mainly urbanized zones, account for a notable share of the island’s surface.