The Mediterranean has been identified as one of the most responsive regions to global climate change1, with observed warming expected to continue at a greater rate than the global average2. Consequently, the Mediterranean is well-defined as a hotspot area according to observations and future projections3,4. This characterization was first underscored by the application of the Regional Climate Change Index (RCCI)5, designed to identify regions most responsive to climate change through assessing future changes in mean conditions and interannual variability of precipitation and near-surface air temperature.

Due to the interest in this area, several studies have been conducted to assess past and future changes in crucial climate parameters. The annual precipitation of the Mediterranean area is expected to show a decrease of about 4% for every $1{}^{\circ }\text{C}$ increase in global temperature. This decrease is expected mainly in the summer season for the northern regions of the Mediterranean basin and across all seasons in the central and southern regions6. Other studies mention a decrease in precipitation for all seasons, resulting in a reduction of annual precipitation that can reach $40\mathrm{m}\mathrm{m}{/}^{\circ }\text{C}$ of global warming in parts of the Balkans, Anatolia, and the Iberian Peninsula7. This decline in precipitation8,9, along with the significant rise in temperatures7, has led to higher evaporative demand, increasing drought severity10. Future climate change scenarios from various model experiments also agree on an increased frequency and severity of droughts in the Mediterranean basin11,12.

Another crucial climate parameter showing a significant increasing trend, particularly during the summer months, is extreme high minimum temperatures, which have broad impacts across various sectors. For instance, in the Eastern Mediterranean, specifically in Israel, indicators related to high minimum temperatures have shown a marked increase, rising by $7{}^{\circ }$C per decade from 1988 through 201713. Similarly, for a longer period (1961–2020), a significantly increasing trend in extreme minimum temperatures has been observed in the Montenegro region, another part of the Mediterranean14. These changes are particularly important as they often represent nighttime temperatures, which can contribute to heat stress and have direct consequences for human health and ecosystems15.

Apart from the changes in mean climate conditions, another important aspect of global warming is the increase in the frequency and intensity of extreme weather events. Xu et al.16 introduced the Regional Extreme Climatic Change Index (RECCI), a global index that combines seven extreme climatic indices, focusing on changes in the frequency, intensity, and interannual variability of temperature, precipitation, and wind speed extremes. According to this index, the Mediterranean shows a comparatively lower response to climate change than other regions, such as Alaska or the Amazon Basin. However, despite this global assessment, several studies have emphasized the need for a deeper analysis of extreme events specifically within the Mediterranean. Frequent and intense occurrences of extreme events in this region pose significant risks to key sectors, including agriculture17, health18, and tourism19, underscoring the region’s specific vulnerabilities to climate change. For instance, over the next century, a strong increase in the frequency and intensity of heatwaves are expected, with this outcome being robust across most climate models and scenarios20,21. Extreme rainfall has shown an upward trend in numerous northern Mediterranean regions and is expected, with high confidence, to increase further and probably be accompanied by an upsurge in flash floods, while no significant change is expected in the south6,22. Despite the overall uncertainty, the absolute rainfall maxima (e.g. 1-in-50-years daily extremes) are expected to become more intense throughout the region23.

Taking into account all the above, it is highly important to conduct a deeper analysis of such hotspot areas, where, on one hand, the effects of climate change are more pronounced, and on the other hand, the capacity to adapt is not equally distributed across the entire region. Hence, the present study aims to identify the most vulnerable sub-regions within the Mediterranean area, focusing on areas responding to either mean climate values or extreme events. This approach provides critical insights for future research, highlighting specific locations that require increased attention due to their susceptibility to climate change impacts. However, several studies assess the behaviour of climate parameters in the Mediterranean and mention parts of the basin where historical changes are more intense, a more holistic and rigorous analysis is still missing, according to the authors’ knowledge.

The primary objective of the present research is to identify the most vulnerable sub-areas in the Mediterranean using two climate indices, the newly introduced Mediterranean Hotspot Index (MED-HOT) and the well-defined Regional Climate Change Index (RCCI)5. While the RCCI index is widely recognized for identifying climate hotspots based on changes in mean climate parameters, it has a key limitation: it does not account for changes in climate extremes—both in terms of frequency and intensity—which are critical drivers of climate impacts, particularly in the Mediterranean basin. Climate extremes, such as heatwaves, intense rainfall, and droughts, often have a much greater impact on ecosystems, economies, and societies than changes in average climate conditions alone. To address this gap, we developed the MED-HOT index, which specifically focuses on changes in these climate extremes. By integrating the MED-HOT index with the RCCI index, our approach provides a more comprehensive assessment of climate vulnerabilities in the region. The RCCI index highlights regions affected by broader shifts in mean climate, while the MED-HOT index emphasizes areas where extreme weather events are becoming more frequent and severe. This dual approach ensures that we capture all critical hotspots, including those where the mean climate may not show significant change but where extreme events have substantial impacts. The inclusion of the MED-HOT index significantly enhances our analysis, offering a deeper understanding of vulnerabilities in the Mediterranean region by accounting for both mean climate changes and the increasing relevance of climate extremes. The MED-HOT index incorporates four key indicators of extreme events typically affecting the region: extreme maximum and minimum temperatures, intense precipitation, and droughts. By combining both indices, this study identifies the most vulnerable sub-areas, allowing for targeted, region-specific analyses. This, in turn, can help develop more effective strategies to mitigate the regional impacts of global warming and the associated socio-economic consequences.

Classification of MED-HOT index and its spatial analysis

The MED-HOT index is designed to assess climate vulnerabilities in the Mediterranean region by integrating changes in the frequency and intensity of four extreme climate indicators: extreme maximum temperature (TX90), extreme high minimum temperature (TN90), extreme precipitation (P95), and consecutive dry days (CDD). This index reflects the primary climate challenges faced in the region, including heatwaves and droughts. To compute the MED-HOT index, the analysis divides the available data into two periods: the early historical period (1981–2000) and the late historical period (2001–2022). For each index, the frequency and intensity of extreme events are calculated and then normalized. The final MED-HOT index is derived by summing the normalized differences in frequency and intensity across the four indicators, providing a comprehensive measure of climate vulnerability. While the theoretical maximum value of 8 can be achieved if all eight components reach their normalized maximum value of 1, this scenario is highly improbable in practice. Each grid point is analyzed independently, and it is unlikely for a single grid point to exhibit the maximum values for all eight components simultaneously. For instance, a grid experiencing the maximum value of extreme temperature (TX90) often does not coincide with the grid experiencing the maximum value of the P95 precipitation index. These extremes typically occur under different climatic regimes and locations. Additionally, both the frequency and intensity of each indicator are analyzed separately, making it even rarer for a grid point to exhibit the maximum values for both components at the same time. For example, a location experiencing the most frequent extreme precipitation events may not record the highest precipitation intensity simultaneously. This further decreases the chances of reaching the theoretical maximum. As a result, the observed MED-HOT values across the Mediterranean range from zero to three. Nevertheless, these values still represent significant climate extremes and should not be interpreted as indicating only moderate impacts of climate change (Fig. 1).

It’s important to clarify that the MED-HOT index is comparative, following the definition used in Giorgi’s RCCI index. A lower value of the MED-HOT index does not necessarily indicate a small absolute change within a grid point. Instead, it reflects a smaller climate response relative to other grid points in the study area. This approach highlights the relative changes in climate response across the region, rather than directly measuring the absolute magnitude of change.To better understand the index’s spatial distribution, values have been classified into five categories (Fig. 1). Areas with index values below one are categorized as the first class, indicating minor changes and non-hotspot areas. The remaining areas are divided into four additional categories, each with a 0.5 range. This classification allows us to effectively capture the variability of both indices while minimizing the introduction of noise.

The classification of the MED-HOT index is depicted in Fig. 1. The western part of the Iberian Peninsula, along with the majority of central and eastern parts of North Africa, fall within the first class, indicating relatively low MED-HOT values compared to other areas. The next two classes, with MED-HOT values from 1 to 2, are the most prevalent. Almost all grids located in the western part of the studied area (latitudes lower than 10 degrees north) belong to these two classes. Additionally, a significant extent of the Balkan Peninsula, as well as the central and northeastern parts of the studied area, fall into these two classes. In the last two classes, where the index reaches its maximum values, the areas become more specific. Particularly, the eastern regions of Spain, the Dalmatian coast, the Alps, limited regions in the eastern Mediterranean, and areas of northern Greece and Turkey exhibit the highest values of the MED-HOT index.