Land provides the main basis not only for human livelihoods but also for well-being. It endows means for agriculture practices thus contributing to the food supply, also providing freshwater, and fostering biodiversity in the several intricate ecosystems [1
]. Land use also plays a relevant role in the climatic system, being closely intertwined [2
]. As such, climate change, as well as climate and weather extremes, are important stress factors to land ecosystems and biodiversity, which are thus becoming increasingly vulnerable [3
]. Global population growth has implications for global food consumption, raw materials, and energy. An expansion of areas under agricultural and forestry systems [5
] is, therefore, required to warrant food security. However, land-use intensification can decisively contribute to land/soil degradation and, henceforth, potentiates desertification [7
Climate change has already deeply impacted biodiversity, ecosystems, and agroforestry systems [9
]. Global warming and changes in the precipitation patterns are fostering an increase in arid/dry regions, and ultimately the expansion of desertic areas. Climate change has increased the frequency, intensity, and duration of extreme events, such as droughts and heatwaves, namely in the Mediterranean region [12
]. Changes in precipitation spatial patterns and temporal regimes not only affect the water content in reservoirs but also soil water availability [16
]. These modifications in the regional climatic features are reflected on different time scales, from the annual-mean conditions to seasonality, daily cycle, and variability [18
], which in turn affect crop-relevant bioclimatic conditions, such as growing season length, thermal forcing, chill accumulation or water availability for irrigation [19
Changes in temperature and precipitation patterns are key factors triggering shifts in the climate of a region. These variables are fundamental to classify climates in different categories, such as in the Köppen–Geiger climate classifications system [22
], but also for the Worldwide Bioclimatic Classification System (WBCS) [23
]. Recent studies projected changes for the Iberian Peninsula (IP) not only for the Köppen–Geiger climatic classification [25
] but also for the major divisions of the WBCS, mainly for the IP southernmost regions [11
]. Since 1986, the IP has experienced an acceleration of land use for agriculture and forestry, promoted by the integration of these countries into the European Union [26
]. The European Union’s reform of the agriculture policies, under the Common Agricultural Policy, CAP, was a key factor for the observed changes, also observed in agricultural practices and cultivated species. Overall, these factors (climate and policies) jointly exacerbated land degradation, which is already particularly apparent in coastal areas, drylands, river deltas, riverine estuaries, permafrost, amongst others. Therefore, sustainable land management [27
] is urgent to balance these projected changes, while maintaining crop yields, animal growth rates, water management, soil health, and land conditions [28
The Portuguese viticultural sector is of major socioeconomic relevance, owing to the relatively high generated economic income and the important share of national exports [29
], currently being Portugal the 10th wine exporter and the 11th wine producer [30
]. Mainland Portugal has a total of 12 wine regions (WR), with a fluctuation of vineyard land cover from 271,507 ha in 1989 to 189,668 ha on 31/07/2020 [31
] (Supplementary Materials Figure S1; Table S3
). With an opposite trend, wine production increased from about 5.8 Mhl in 2009/10 to about 6.5 Mhl in 2019/20 [32
] (Figure S2
). Different denominations of origin (DO) can also be found within each WR (Figure S1
On the other hand, the production of olive oil is also highly relevant to the Portuguese economy. Although Spain is the world’s leading producer, Portugal, with a production of about 100,000 tons, currently holds the seventh position in the world production ranking, along with Turkey (183,000 tons), Tunisia (120,000 tons), and Morocco (200,000 tons) [33
]. These rankings in both viticulture and oliviculture are particularly noteworthy taking into account the relatively small size of the country and are thereby key factors for its socio-economic development.
The main goal of this research aims to answer the question: ‘Are land use options in viticulture and oliviculture in agreement with ongoing bioclimatic shifts in Portugal?’. This is a highly relevant question since, water management in viticulture and oliviculture demands adaptation strategies of these industries to climate change, while minimizing environmental impacts. This is particularly important not only for Portugal but for the Mediterranean regions increasingly exposed to extreme climate events [1
]. Therefore, this assessment is of utmost relevance.
To answer the aforementioned question, the Köppen–Geiger climatic classification and the WBCS were applied in the first step, while a comparison between two 30-year periods, namely 1950–1979 and 1990–2019, was carried out to relate recent past climatic shifts with land-use changes. From the WBCS, which encompasses the bioclimates, the thermotypes, and ombrotypes, a compound bioclimatic-shift exposure index (BSEI) was computed to identify the most exposed regions in Portugal to bioclimatic shifts. In a second phase, the spatial patterns for the extension of vineyards and olive groves for 1990, 2018, and between 1990–2018 are presented. Subsequently, correlations between ombrotypes and thermotypes were calculated for 1990, 1995, 2007, 2010, 2015, and 2018.
The present climatic characterization aimed at identifying the regions in mainland Portugal that have endured the most significant bioclimatic shifts from 1950–1979 to 1990–2019. Most of the areas or districts that experienced more accentuated alterations in the bioclimatic classes from one period to the other are located in northwestern Portugal. For the second period (1990–2019), satellite-based land cover data are available throughout the country on an annual timescale. Therefore, the evolution of vineyard and olive grove areas was analyzed to assess to what extent have these crops been expanded to more susceptible zones to bioclimatic shifts. To our knowledge, there are no related studies regarding oliviculture and viticulture that use the Köppen–Geiger climatic classification, the WBCS, as well as the compound BSEI to evaluate the bioclimatic shifts. Therefore, it was not possible to compare the methodology used in this study since there are no similar cases for comparison.
The evolution in the vineyard cover area from 1990 to 2018 (Figure 7
a) shows a bidirectional displacement, towards the regions with more extreme bioclimates in the territory. The vineyard area has been increasing in the relatively cool and humid regions of northwestern Portugal (Vinho Verde WR), as well as in the warm and dry regions of southern Portugal (Alentejo WR) (Figure S1
). In effect, from 2018 to 2020, vineyard areas have increased in the north, e.g., in Minho 2267 ha, in Douro/Porto 3212 ha, but also southern Portugal, in Alentejo VR 513 ha (Table S3
). These regions are, nevertheless, located in areas for which the BSEI indicates stronger bioclimatic shifts during the last decades (Minho WR, Douro/Porto WR, and Alentejo WR). Even though the increase in the vineyard area in regions with cooler and more humid climates can be considered a climate-smart adaptation strategy, thus enhancing the climate resilience of the sector, the pronounced bioclimatic shifts observed in these regions may considerably affect the regional terroirs and, as a result, the wine typicity and style [40
]. In addition, the emergence of vast areas with irrigated vineyards under the typically warm and dry conditions of southern Portugal will threaten the already limited water resources [41
], thereby requiring more efficient water management and water-saving agricultural practices. The lack of water availability may indeed challenge the future sustainability of the sector in this region. This will be particularly relevant under the projected future warmer and drier climates, which will exacerbate the current warm and dry conditions, becoming irrigation even more vital [20
As for viticulture, the olive grove land cover in Portugal has been changing between 1990 and 2018 (Figure S3
). These fluctuations have also impacted olive yield, which was approximately 700,000 t in 2019 (Figure S4
). The recent area expansion occurred mainly in the Faro, Beja, Vila Real, and Bragança districts, the last two showing relatively high BSEI (Figure 6
b). Regions in the north are indeed gradually experiencing climatic conditions that were more typical of southern Portugal a few decades ago and are, thereby, becoming more suitable for oliviculture. Although the area of olive groves has undergone a significant increase in southern Portugal, most of them irrigated, the progressively higher relative coverage in cooler climates, still predominantly rainfed orchards, may already suggest higher awareness and a more or less conscious attempt of the sector to adapt to the ongoing climate change. It is worth mention that the construction of the Alqueva dam in the Guadiana River, which has created one of the biggest artificial lakes in Europe had a huge impact in the inner southern region of mainland Portugal. The increase in the regional water resources, allowed the implementation of a wide water distribution and irrigation systems. This fact influenced the expansion of vineyards and olive groves, among other cultures in this region during the timeframe analyzed in this study.
The present study assessed the climate change trends that have already influenced the Köppen–Geiger climate classification and the WBCS between 1950 and 2019 in mainland Portugal. For this purpose, a comparison between two 30-year periods, i.e., 1950–1979 and 1990–2019, was undertaken for these two climate classifications. It is worth mentioning that these calculations were carried out using high-resolution gridded datasets, with approximately 1 km grid resolution, thus providing accurate and detailed information throughout the country. To our knowledge, this is the first study analyzing these climate classifications in Portugal at such a high resolution.
The spatial representation of the Köppen–Geiger climate classification revealed three climate types (Figure 3
a) in 1950–1979. The leading climate type was CSa, in 53.9% of the territory, CSb in 45.8%, and a very small percentage of 0.03% for Cfb. The CSa type was predominant in the southern half of Portugal and a narrow region in the south of the Vila Real and Bragança districts (Figure 1
a and Figure 3
a). The CSb was dominant throughout most of the northern half of Portugal, mostly northwards of the Tagus River basin. However, a clear bioclimatic shift in 1990–2019 was detected, with an increase of +18.1% in CSa type, associated with hot summers, and a corresponding decrease of −17.8% in CSb, associated with warm summers, and therefore, a milder climate (Table 5
). These findings are in general agreement with Andrade and Contente [25
The results also hint at shifts in the WBCS four major divisions from 1950–1979 to 1990–2019, related to a decrease of −5.11% in the temperate macroclimate in the northwest, followed by an increase in the Mediterranean macroclimate. This change impacted the bioclimates since a transition from three bioclimates in 1950–1979 to four bioclimates in 1990–2019 was identified, with the decrease of −5.14% for Teoc, counterbalanced by an increase of +4.78% for Mepo. As previously, these changes have occurred mainly in the northwestern regions of Portugal (Figure 4
a,d). The ombrotypes changed from seven to eight types (Figure 4
b,e), with a new ombrotype, Sas, within the semi-arid ombrothermic horizons, corresponding to +0.74% of the territory in 1990–2019 (Table 6
). The overall decrease of −12.17% in the percentage of the territory of humid and hyper-humid regions (Sui, Hui, Hus and Hhi), in detriment of an increase of +24.81% of semi-arid and arid for 1990–2019, is particularly noteworthy.
For the thermotypes, a loss of 7.12% in the percentage of the territory associated with all temperate thermotypic horizons was found (Table 6
). Within the Mediterranean thermotypic horizons, changes were also found. There was a major increase in the thermomediterranean horizons of +18.9%. For the mesomediterranean horizons, a decrease of −8.10% for Mmei, an increase of +4.74% for Mmes, followed by a loss of −8.9% in supramediterranean thermotypic horizons were identified in 1990–2019. Overall, in the southern half of the country (Figure 4
c,f), a gain of thermomediterranean horizons, associated with more arid/dry conditions, was observed. On the other hand, the loss of both Mediterranean and temperate thermotypic horizons, with milder conditions, was registered in the northwesternmost regions. Climate shifts were observed in the major divisions of the WBCS classification are in clear accordance with the study of Andrade and Contente [11
] for the IP. The changes in WBCS have direct implications in the regional exposure to bioclimatic shifts, measured by BSEI. At the district level, the Braga district (in the northwest) is the most exposed (BSEI = 3), followed by Viana do Castelo, Vila Real, Porto, also in the north, Viseu and Guarda in the center; and Évora in the south (BSEI = 2).
For both grapevines and olive trees, which are major crops in Portugal, the results highlight the growth in their land cover areas in southern regions that are becoming dryer. Furthermore, the vineyard area is increasing in the northwest, in regions that present higher values of BSEI, hence more exposed to recent past bioclimatic shifts. This may significantly affect the regional terroirs, grape berry attributes, and wine typicity and style. Conversely, the relative share of southern Portugal to the total olive grove area has been decreasing, which may already suggest an adaptation strategy of the sector, by progressively relocating olive orchards in northern regions that are currently experiencing similar conditions to those found in southern regions a few decades ago.
Both viticulture and oliviculture may be particularly challenged under future climate change scenarios, as suggested by Fraga et al. [20
] for viticulture in Portugal, or by Fraga et al. [42
] and Fraga et al. [43
] for olive yields in Portugal and the Mediterranean region, respectively. As a result, better planning of the distribution of these key crops in Portugal should be envisioned, avoiding the increasing dependence on irrigation, which will eventually disrupt local and regional surface and underground water resources [44
]. New agricultural practices and options are urging to enhance the water use efficiency of crops [45
]. New water-saving and go-green policies and strategies will be particularly relevant under the projected future warmer and drier climates in Portugal [40
]. On the other hand, warranting the future environmental and socio-economic sustainability of these sectors is of foremost relevance for the national economy and food security, thereby deserving further research. As similar problems can be found in many other regions with Mediterranean-type climates, the main outcomes from this study can be easily extrapolated to other countries worldwide.