What are the different climate change scenarios? What are the implications for the natural and agricultural landscape of northeastern Greece?

The study area reveals a shift toward xerothermic environments over time, with significant bioclimatic changes projected under the extreme RCP8.5 scenario. By 2100, de Martonne projections indicate that around 40% of agricultural areas in the eastern, southern, and western regions will face Mediterranean and semi-humid conditions, requiring supplemental irrigation for sustainability. The Emberger Index predicts that approximately 42% of natural and agricultural landscapes will experience sub-humid conditions with mild or cool winters. In comparison, 5% will face drier humid/sub-humid, warm winter conditions. These foreseen futures propose initial interpretations for key landscape conservation, natural capital, and ecosystem services management.Climate is the main driver of natural vegetation and agricultural landscape evolution [1,2]. Understanding the effects of climate, both currently and in the near and far future, is one of the most critical aspects of effective planning for landscape conservation and management and agricultural sustainability. The warm–temperate regions of the world,distinctive biomes characterized by dry summers and wet winters (Mediterranean climate), are especially vulnerable to the effects of climatic variability and the change in climate [3]. This is critically important in the Mediterranean, where a long-term coevolution of natural and cultural landscapes is documented [4]. Mediterranean Europe provides examples of some of the most complex and heterogenous landscapes and local climatic conditions in the continent, rendering intriguing problems in climate-driven landscape change prediction [5] and climate-change adaptation planning. In fact, in recent times, effort has been invested into re-evaluating the historical impact on traditional landscape development; it has long been said that the Euro-Mediterranean is too complex to allow for simple generalizations [6]. Anthropogenically induced climate change (CC) ranks high in the scientific interest hierarchy due to its expeditious spatiotemporal development and menacing nature [7]. The associated modified bioclimate poses considerable threats to the survival of living organisms, the sustainability of natural landscapes, the viability of agricultural activity, the conservation of natural resources, the maintenance, improvement, deterioration, or loss of ecosystem services, and the efficiency of management policies [8–14]. In the coming decades, Greece will appear as climatically pressurized owing to the marked transformation of the bioclimate that is already arising over the entire territory [15–17]. CC projections demonstrate notable warming under the impact of the extreme RCP8.5 climatic scenario [18,19]. By the year 2100, the near-surface temperature is expected to rise by an average value of 4.3 ◦C, resulting, thus, in a significant increase in night frosts, continual dry-spell days, and the annual number of hot days and tropical nights and growing season length and a reduction in frost days. The foreseen increase in the annual number of consecutive dry days of 30% (15.4 days) and the concomitant decline of 16% to 40% of seasonal precipitation underline a crucially drier bioclimatic footprint in the years to come [20–23]. Additionally, in the overall concept of both the projected and observed CC, the present and expected extreme weather events appear as more frequent and intensified (e.g., more severe and prolonged drought events; earlier starts and later ends of heatwave periods; and increasing trends of heavy precipitation), highlighting the climate crisis impacts on human security [24–27]. Climate projections over Greece, in conjunction with its present rather dry thermal climatic regime, give grounds for the country’s escalating susceptibility to the phenomenon of CC, which may induce far-reaching impacts on its extensive natural ecosystems and highly heterogeneous agricultural sector [28,29]. Several present and foreseen effects of CC on the natural landscapes of Greece include significant habitat alterations and elevated extinction risk for autochthonous species and vegetation communities (see, e.g., the Juniperus drupacea forests of Greece) [30], an increase in drought-related tree dieback [31], declining tree productivity and development [32], a reduction in habitat-suitable areas [33], projected altitudinal and elevational shifts and extinctions of endemic species [34], the spatial redistribution of species, invasions and biodiversity loss [35], an increased likelihood of severe wildfires and floods [36,37], and projected altered fire behavior [38]. Some of the CC impacts related to rural and agricultural areas may involve the northward shift of the agro-climatic zones [39], crop production quality decline and quantity limitation [17,40], effects on the capacity of crops to adapt [41], increased susceptibility of crops to extreme weather [42], differentiations in the geographical expansion of cultivations [43], alterations in cultivation area suitability [44], soil erosion and risk of land desertification [45], impacts on groundwater quantity and quality, limitations of surface water availability [46,47], changes in crop phenology [48], increased growing season length [49], and negative social and economic development trends in rural areas [50].Temperature and precipitation are fundamental climatic parameters and are decisive inputs for the investigation of CC. However, the overall comprehension of the magnitude of CC and its impacts on vegetation and vegetation types’ distribution is far better expressed and achieved by applying bioclimatic indices [51–53]. The bioclimatic indices’ major significance as tools for categorizing bioclimates is indisputably exhibited by their broad exploitation in climatological, bioclimatological, and agricultural research studies [54,55]. Approximately one hundred years ago, the de Martonne bioclimatic index (DMI) was proposed for the evaluation of a specific environment’s dryness degree by categorizing it into seven (7) classes, from “dry” to “extremely humid” based on the fundamental climatic parameters of air temperature and precipitation [56,57]. The DMI has been extensively implemented for the classification of the bioclimate due to its reliability, effectiveness, and validity [58,59]. Scientific investigations that frequently employ the DMI fall within the fields of climatology/bioclimatology and agricultural and land or water resources management, while the index also appears as a serviceable tool for achieving environmental assessment reports [58,60–63]. The Emberger Index (EI), commonly described as the “pluviothermic quotient Q”, categorizes the Mediterranean area’s bioclimate zones corresponding to a scheme extending from the “Per-Humid” to the “Per-Arid” type of bioclimate or bioclimatic category established on the parameters of temperature, precipitation, and evaporation. Estimations of the EI include the representation of the annual temperature by the average maximum temperature value of the hottest month (M) and the average minimum value of the coldest month (m), considering that vegetation growth appears dependable on these thermal limits. Precipitation (P) is expressed on an annual basis. At the same time, evaporation is indirectly represented by the difference between the two temperature values (M—m), owing to the EI’s increase with the latter parameter [64–66]. Also, a simplified algorithm based on the minimum winter temperature (m) falling within the range of the “Very Hot” to the “Very Cold” temperature characterizations is applied, serving the purpose of the phytoclimate classification in bioclimatic subtypes, often termed as the “Q2” [66,67]. Thus, an area’s phytoclimatic footprint is characterized through the combination of the bioclimatic types of characterizations derived from the estimates of the Q values along with the temperature conditions based on the estimates of the m values, which results in the Emberger’s Q2 bioclimatic subtypes; for example, a Q2 subtype may be described as the “Semi-Arid, Mild winter” subtype. Within the changing climate’s research framework, studies involving the implementation of the DMI and EI indices are somewhat limited in Greece. For example, Baltas [68] has denoted the variability of aridity in Northern Greece from 1965 to 1995 as being derived from the DMI characterization range of the semi-dry to very humid bioclimates. The same author estimated the bioclimatic footprint of the entire country, which described the dry to very humid classes. Another study in Northern Greece conducted by Mattas et al. [69] on the upper agricultural area of the Gallikos river basin has revealed bioclimatic variations from semi-arid to humid conditions based on climatic data over a 27-year period (1980–2006). Also, mountainous regions have been classified by Sidiropoulou et al. [70], who have characterized, respectively, northern Greece’s Mt Vermio and southern Greece’s Mt Zireia as moderately humid and humid, respectively, on the basis of climatic data during the years 1990–2019. Lappas et al. [71] revealed the bioclimatic conditions of a water district in eastern–central Greece, illustrated by the arid to very humid classes over the 1980 to 2001 timeframe. A moderate trend, between the years 1958 and 2011, toward a more dry thermal regime over the traditional agroforest system of Thriasio Plain (northwest Athens) has been shown by Mavrakis et al. [72]. Further south, Beloiu et al. [73] pinpoint the transition of Crete Island’s bioclimate from very humid to humid conditions over the 1979–2013 period. Evidently, most utilizations of the DMI concern bioclimatic studies based on past timeframes, while there has been no application, until recently, of the EI over the entire country involving past, present, and also future time-periods [18,19]. This highlights the limited scientific knowledge on the future bioclimatic development on a local scale over natural and agricultural areas, with no applications of the DMI and EI as tools for bioclimatic categorization and for projections on conditions owing to CC foreseen on a local scale in Greece. The motivation, therefore, for the conduction of the present investigation lies in the relatively limited scientific outcomes related to DMI and EI applications, along with the critical need for the protection and preservation of the natural and agricultural landscapes already threatened by the changing bioclimatic conditions. More specifically, in this study, the bioclimatic DMI and phytoclimatic EI indices are computed. Their categories are spatiotemporally illustrated, for the first time, for the present (1970–2000) and future (2030–2060; 2070–2100) climate conditions at very high resolution (~500 m) and under two specific greenhouse gas emission scenarios, namely RCP4.5 and RCP8.5. Overall, and under the framework of the LIFE-IP AdaptInGR National Project, the main objective of the present study is to outline the significant short-term and long-term bioclimatic alteration trends that are foreseen to occur and shall undoubtedly impact the already pressurized natural and anthropogenic ecosystems in northern Greece. The resulting mapping of the spatial distributions of the bioclimatic or aridity indices’ classes, coupled with the spatial statistics per class, period, and emission scenario, may be valuable tools for conducting further environmental research in the broader framework on the conservation of landscapes threatened by CC. The outcomes aim to support decisions and policy-making for regional natural capital, ecosystem services, and agricultural development management to adapt and mitigate future predicted conditions. The abovementioned approach offers novelty to the presented study and robust outcomes for further investigation.Conclusions: The study outcomes outline the bioclimatic change over the natural and agricultural landscapes of the region of Eastern Macedonia and Thrace, northeastern Greece. Thus, the present study’s innovative findings resulting from the application of both biocli-matic indices (de Martonne Index; Emberger Index) may be summarized by the following major conclusions: (a) Profoundly altered bioclimatic regimes predict trends toward more xerothermic environments under the two examined emission scenarios RCP4.5 and RCP8.5. Comparisons between the three study time frames (1971–2000; 2031–2060; 2071–2100) highlight the temporal development in the direction of more dry thermal conditions, as predicted under both emission scenarios. (b) Significant changes following the implementation of the de Martonne Index concern the long-term timeframe of the extreme RCP8.5 scenario. Owing to high emission regimes and associated global warming, by the end of the century, the more xerothermal Mediterranean and semi-humid conditions will account for approximately 40% of the investigated area. The parts to be particularly influenced are the eastern, southern, and western agricultural areas, which are projected to require increased supplementary irrigation. Natural areas may also be increasingly stressed due to reduced humidity and precipitation regimes. (c) As documented by the Emberger Index, the spatiotemporal xerothermic evolution over the investigated area follows a north–south direction. An intensified xerothermic trend under the extreme RCP8.5 is also projected by the Emberger Index in the long run. By the year 2100, a substantial part of the natural and agricultural areas amounting to nearly 42% is projected to be impacted by sub-humid, mild winter conditions and up to nearly 33% by sub-humid, cool winter conditions. The possible existence of warm winter combinations expected to impact both agricultural and natural landscapes (distribution of nearly 5%) underlines the peaking of the bioclimatic shift toward warmer and drier conditions. Moreover, the xerothermic tense can potentially cause adverse effects on a surface larger than half of the study area, containing high-value agricultural and natural areas. (d) Finally, a multi-scaled approach at the regional level should be helpful in planning for natural capital conservation, restoration, and sustainability initiatives at the landscape level. This particular studied area is diverse and complex and has several high-profile and well-studied protected natural areas or other designated areas of outstanding interest, both in its natural/semi-natural and cultural landscapes. However, new pressures from climate-associated stress may create severe problems associated primarily with water-related ecosystem services, i.e., water stress in agricultural and aquatic, wetland, and riparian areas accompanied by wildfire frequency increases. Climate adaptation analysis would require a scientifically informed and guided landscape approach. It should not be relegated only to specific landscapes or high-profile protected areas as has already been carried out in some recent initiatives. Also, it is important to carefully assess where adaptation and mitigation measures may conflict with nature conservation initiatives. It is recommended that landscape-scale approaches be taken to promote climate adaptation and climate-smart planning initiatives throughout the region of Eastern Macedonia and Thrace.

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