The Adaptation and Resilience of Urban Green Spaces in Quinta do Lago, in Southern Portugal (Algarve), Using Xerophytic Vegetation – A Review

1. Introduction

The consequences of drought, a climatic phenomenon characterized by prolonged periods of precipitation absence [1], which once impacted mainly on the agricultural sector, is now a multi-sectoral issue [2]. Low water availability has always been part of the Mediterranean climatic context and different anthropogenic activities have developed over time as a result of this climatic phenomenon [3]. However, the Mediterranean basin currently has a population of more than 500 million inhabitants and is one of the world’s main tourist destinations [4], which causes a huge pressure on the region’s naturally scarce water resources. Portugal is one of the European countries with the highest volume of water withdrawn per inhabitant, yet, at the same time, represents one of the lowest levels of efficient water use efficiency [5]. It is therefore essential that urgent consideration be given to the implementations of appropriate policies and strategies for the sustainable water management, to avoid catastrophic economic, social and ecological losses. These losses can translate into an increased risk for food and energy security, since they affect the soil’s water balance, which consequently leads to scenarios of agricultural and hydrological drought [6].

The negative trend in precipitation anomalies recorded in the administrative region of the Algarve since 2012 [7], has a frequency and severity that has been increasing [4], anticipates a future scenario with serious constraints on the management of public water supply, due to reduced streamflow or groundwater availability. This will have significant impacts on socio-economic activities, particularly the tourism, a main economic pillar of the region, and on the well-being of local populations [8].

The technical and scientific knowledge of any proposed composition of flora within a plan for landscaping is of fundamental importance to the long-term sustainability and continuity of the project. The study of native plant communities [9], especially those occurring in edaphoxerophilous positions or high xericity, is essential in the species selection process, for green spaces, because it provides an ecological basis, directly related to the sustainability and maintenance of these spaces, since their edaphoclimatic requirements are compatible with the reality of local natural resources, contributing to the resilience of green spaces [9]. Moreover, the study of plant communities allows understanding of natural plant associations, contributing for the balance and aesthetic value of the green space, and also avoids the selection of invasive plant species [10]. This approach enables the design of more resilient green spaces, better adapted to climatic challenges. In the specific case of the Algarve, they are primarily related to low water availability. Urban green spaces provide numerous ecosystem services, offering environmental, ecological, social, economic, and human well-being benefits [11]. In the particular case of the Mediterranean basin, these services play a pivotal role in mitigating droughts and floods [12]. However, the application of xerophytic vegetation in urban green areas, such as the Mediterranean basin, must adhere to specific criteria based on regional climatic dynamics [13]. Given the scarcity of water resources and the occurrence of elevated temperatures, during the summer months, it is imperative for these areas to adopt the integration of xerophytic species that promote evaporative cooling through the process of shading and low - and slow-growing xerophytic vegetation, which are distinguished by their reduced water requirements [14]. Achieving an equilibrium between thermal comfort and water consumption is essential to reduce urban temperatures while simultaneously maintaining minimal water utilisation. Additionally, the presence of xerophytic vegetation has the potential to reduce surface runoff, thereby helping to prevent flash flooding precipitated by periods of intense rainfall [15].

According to the bioclimatic model (Bioclimatic Classification of the Earth) developed by Rivas-Martínez [Rivas-Martínez (1981, 1982, 1987, 1996, 2005, 2007, 2008) and Rivas-Martínez et al. (1988, 1991, 1997, 2004)], the Algarve region is included in the Mediterranean macrobioclimate, characterized by well-defined xericity and high precipitation periods [16]. The influence of these bioclimatic conditions has resulted in a highly diverse flora, comprising approximately 25 000 species [17]. This has also led to the development of numerous adaptive mechanisms that allow these species to overcome prolonged drought periods and natural disturbances, such as wildfires, which are typical of this landscape [18]. Additionally, the irregular precipitation patterns associated with this macrobioclimate, both spatially and temporally, result in years of severe drought, alternating with years of abundant precipitation, phenomena that have been intensified due to climate change [19]. Considering that water resources are one of the main constraints for the implementation of green spaces [20], particularly in drought-prone regions, it is essential to develop water management adaptation strategies. Among these, the use of xerophytic vegetation, preferably native species, is crucial [16]. The morphological and physiological features of these plant species are a response to the xeric environment that surrounds them and they have developed numerous adaptation mechanisms that allow them to manage water efficiently during long periods of drought [21]. However, aesthetic concerns [13], mainly driven by widespread misinformation, have led to the dominance of exotic vegetation in the region’s green spaces [20]. This contemporary landscaping model, prevalent in the Algarve, has contributed to increasing water imbalances, as garden irrigation can account for up to 70 % of a single-family home’s water consumption [22]. Beyond its impact on water resources, another well-established phenomenon in Mediterranean green spaces has been the increasing introduction of invasive species [23]. Currently, the estimated economic losses associated with invasive species in Europe exceed €12.5 billion per year, with significant socio-economic and ecological impacts [24]. Tourism is identified as a significant facilitator of the dispersal of invasive species [25], a factor that must be considered in the territorial planning and management by the competent authorities, especially in the Algarve region, where tourism is the predominant economic activity. Additionally, climate change is affecting the distribution patterns of these species, leading to a gradual replacement of native tree layers by exotic vegetation that has greater establishment and growth capacity across the Mediterranean basin [26].

This research, part of the main author’s doctoral dissertation, corresponds to the first stage, a literature review and study area description, of a broader investigation, as part of the doctoral dissertation of the main author. This investigation is divided into three stages:

1) Literature review and study area description - The literature review was guided by the main objective of summarising and exploring the main themes and concepts inherent to xerophytic vegetation in urban green spaces, in a context of low water availability, through research studies and scientific literature, preferably developed in regions with edaphoclimatic features similar to those of the study area, which associate the ecological and socio-economic factors of green spaces with the promotion of their adaptation and resilience to the recurring phenomenon of droughts. The study area description focused on the most relevant biophysical aspects (geomorphological, hydrological, geological, pedological, climatological, bioclimatological and anthropogenic) and was carried out through the consultation of cartography, using QGIS software, which resulted in representative mapping;

2) Surveys - Since the understanding of the general population is fundamental to the successful implementation of measures to mitigate water scarcity, the public participation component will be introduced in this research, through surveys, to assess the perception of the population and stakeholders [27] (companies that directly or indirectly influence the management of water resources in the study area) about the effects of low water availability and measures to reduce water consumption in green spaces, such as the application of xerophytic vegetation, which is uncommon in the current landscaping model. For the formulation of the survey, the ‘Triangulation’ [28] methodology will be adopted, which covers various adapted data collection processes, so that the perception of each source can be assessed, with the aim of increasing the credibility and validity of the research conclusions [29]. This methodological strategy allows for a more holistic and reliable understanding of the issue, since the surveys do not rely on a single type of question or a single source of response. The group of participants will be defined according to inclusive principles, ensuring gender equality in the sample of participants, considering people with different levels of education, age, ethnicity and social class [30]. In this specific case, of this study area, a seasonal stratified sampling method was chosen [31], due to the large fluctuations in population throughout the year, caused mainly by secondary homes and tourist occupancy, depending on the season. Thus, the year will be divided into three periods: high season (June to August), low season (November to February) and intermediate season (March to May and September to October), with a sample calculated for each of these periods. The questionnaires will be structured according to [32]: a) Introduction - where the purpose of the survey is presented; b) General instructions, which shows how to respond to the survey; c) Demographic data - with basic questions about the respondent’s profile, such as age, gender, education and location; d) Main Body - where the questions are organised into thematic blocks according to the research purpose, with open and closed questions and measurement scales; Closing - which contains a final message of thanks for their collaboration and further instructions. The qualitative analysis of the content of these surveys will be carried out using NVIVO12 software and the quantitative statistical analysis will be carried out using SPSS software. From here will result a map of perceptions on the application of xerophytic vegetation in green spaces and on the effects and consequences of low water availability in the region;

3) Experimental trials - in a controlled environment, at the University of Algarve facilities, using xerophytic species, previously selected according to the literature review conducted in the first phase of the research. The abiotic parameters considered will be, water use, temperature, radiation, nutrition and evapotranspiration, based on data from the main climate change scenarios defined by the IPCC, and the aesthetic quality. Comparative data will be used to determine whether these species are a viable option in the context of climate change and whether the reduction in water consumption is close to that suggested in the literature. For the physical measurements a set of methodologies will be applied to: Water use and Evapotranspiration – using an Automated Weighing Lysimeters (mini-lysimeters), that continuously takes high-resolution measurement of water loss per plant/pot [33]; Temperature – using Infrared Thermometers that measure plant’s leaf temperature to develop a water stress index, allowing for an irrigation schedule [34]; Radiation – using Spectral reflectance, as an indirect method to estimate the plant’s water content and level of water stress [34]; Nutrition – using leaf spectroscopy, a non-destructive method, that allows to assess the changes in leaf compositions, indicating levels of stress; Aesthetic quality – measuring the morphological features such as counting of flowers, leaves or axis, diameters and heights of flowers, the lengths and widths of leaflets and stem length [35]. The data resulting from these experiments will allow better understanding of plant physiology, thus a more efficient way for water management, with more precise water volumes and schedules, and also quantify tolerance limits in order to optimize the adaptability and resilience of those species to climate related impacts, such as droughts.

The decision to choose Quinta do Lago, a tourist resort located on the Litoral Algarve, as a study area, was based on it’s representativeness in terms of urban-tourist green spaces in the Algarve. In addition, this location also represents one of the most important economic pillars of the region, the tourism, intrinsically related to recreation and leisure green spaces, that are part of socio-economic activities, highly dependent on the region’s water resources.

The main goal of this review was to enhance the scientific understanding of how xerophytic vegetation can promote the adaptation and resilience of green spaces in the Algarve, within a context of limited water availability, aggravated by climate change. This research is based on assumptions found in diverse scientific literature, such as scientific articles, reports, theses, books, among others. The information resulting from this research, in all its different levels of complexity, has the potential to enable the different entities that manage green spaces, as well as the scientific community, to prepare adaptation and intervention plans. These plans should aim to promote practices and strategies that contribute to the resilience, maintenance, adaptation and valorisation of green spaces in contexts where water availability is limited, whilst taking into account the prevailing socio-economic activities within the region.

2. Materials and Methods

2.1. Study Area Description

The study area, where this research is conducted, corresponds to the Quinta do Lago tourist resort, located in southern Portugal, in the administrative region of the Algarve, municipality of Loulé. It occupies a total area of 645 ha (Figure 1) and is marked by residential tourism. To the South it’s bordered by the Ria Formosa (Atlantic Ocean), to the East by the Ludo marshland, to the West by other tourist resorts and to the North by agricultural land. The name of this development refers to its location, where a huge lake was formed from the Ria Formosa, giving this area immense aesthetic value [36].

As is it happens in other adjacent tourist developments, low permanent population density is a striking feature of this area, with only 136 people living permanently, corresponding to a population density of 20.37 people/km² [37]. Around 47% of the population is aged between 18 and 64 years, 39% is over 65 year old and 14% is between 2 and 18 years old [37].

Currently, Quinta do Lago consists of housing developments, residential clubs, hotels, shopping centres, car parks, main roads, private and public green areas, several natural and arteficial lakes, golf courses and other recreational and sporting facilities such as tennis, horse riding, sailing, fishing, water skiing and shooting [38]. Of the total number of buildings (1044), around 97% are used exclusively for residential purposes [37], with only 4% of residences being permanently occupied and the rest being classified as secondary residences. This data corroborates what has already been mentioned above, that Quinta do Lago is mainly an area of residential tourism.

The occupancy of secondary residences is highest during the high season, between June and August, with an average occupancy rate of 70% in June and 90% in July and August, with an estimated population of 6000 people. Tourist occupancy is also higher during these months, with an average of 75% in June and 95% in July and August, with 2650 tourists [37]. In the low season, from November to February, the average occupancy rate for secondary residences is 19%, corresponding to 1800 people and tourist occupancy is 25%, corresponding to 1000 tourists [37]. In the mid season, from March to May and from September to October, seasonal residential occupancy does not exceed 60%, with a population of 5400 people and tourist occupancy does not exceed 70%, or 2 650 tourists [37]. This means that during the high season, considering the seasonal residentes and tourists, the population in Quinta do Lago is about 64 times higher than the permanent population (Figure 2), which translates into great pressure on water resources, at a time of the year when the replenishment of these resources is practically non-existent due to low or null precipitation rates.

In the context of green spaces, technical and scientific knowledge of the potential natural vegetation in a given biogeographical area is essential to understand which plant species are best suited to the climatic conditions of a region. However, the isolated study of vegetation is not sufficient for its characterization. It is also necessary to analyse the relationship between climatic factors and vegetation using bioclimatic indices and parameters to determine plant communities distribution areas [16].

According to the bioclimatic classification adopted in the Iberian Peninsula, based on the Bioclimatic Classification of the Earth, developed by Rivas-Martínez ([16,39,40,41,42,43,44,45]) and Rivas-Martínez et al. ([42,46,47,48]), five macrobioclimates (Tropical, Mediterranean, Temperate, Polar and Boreal) can be defined on Earth [16]. The study area is located within the Mediterranean macrobioclimate, characterized by a well-defined dry period, with at least two consecutive months of aridity during the hottest part of the year [45]. This occurs when the average precipitation (mm) is less than twice the average temperature of the two hottest months of the summer trimester [45], which in the case of the study area coincides with the hottest months (July to September). The study area’s average annual temperature is 18.2ºC and the average annual rainfall is 455.1 mm, mainly between November and December [49]. Within this macrobioclimate, the study area is under the influence of the Mediterranean Pluvi-seasonal Oceanic bioclimate, characterized by lower annual temperature variation due to the proximity to the ocean [50]. This reveals the strong oceanic influence to which the study area is subject, where the effect of proximity to the Atlantic Ocean results in greater thermal regulation.

Based on the Thermicity Index (It), the study area is under the influence of a thermo-Mediterranean thermotype (Figure 3), marking this area with mild winter. With regard to the ombric characterization, based on the Annual Ombrotic Index (Io), two distinct ombrotypes can be observed in the study area: lower dry, which occupies 86% of the total area; and upper dry, which occupies 14% of the total area. (Figure 4). In fact, the spatial distribution of precipitation in the Algarve region is clearly the result of the interaction between the topography and the Atlantic air masses, resulting in high precipitation levels in the higher altitude regions of the Algarve mountains, which fall within the sub-humid ombrotype (lower and upper), and low levels in the coastal strip, where the altitudes are significantly lower.

The study area is located on the Algarve coastline and is characterised by gentle slopes, less than 50 m high, which are extremely sensitive to erosion processes [51]. This area was dominated by alluvial deposits, sand and thin dunes [52], before being highly artificialised, with major soil disturbances. Such disturbances, led to the removal of several soil horizons leading to a nutritional imbalance in the soil, thus promoting the dependency on synthetic fertilisers, that leads to soil salinisation, and, consequently to groundwater contamination [53]. According to the Land Use Map for Mainland Portugal for 2018, most of the study area is occupied by build-up areas (50%), golf courses (26%), landscaped green spaces (23%) and ecological spaces (1%) [54].

In the study area it is possible to find 23 private boreholes and 1 municipal borehole [55], connected Vale do Lobo aquifer subsystem [56], where 50% of the water extracted is used to irrigate golf courses [57]. The tourism seasonality associated to Quinta do Lago is responsible for the asymmetries observed in water consumption between the low season and high season, where the water used to irrigate private green spaces is 50 times higher than that used for domestic purposes [58]. In addition, when the concentration of salts in borehole water increases, due to saline intrusion [57], there is an increase in consumption from the public water supply network, which consequently leads to greater pressure on this system.

In terms of nature conservation, the entire study area is covered by the National Network of Protected Areas, with specific areas of high protection under the Natura 2000 Network, where 50.1% of the study area is occupied by Special Areas of Conservation (SAC) and 49.9% by Special Protection Areas (SPA) [59]. The RAMSAR sites only occupies 0.3% of the total study area [60]. This set of legal constraints aims to prevent the deterioration of these natural habitats through measures relating to the management of land use planning in this territory. Despite the existence of these legal constraints on nature protection and conservation, the artificialisation of this area was only permitted because it occurred prior to the aforementioned legislation.

The green infrastructure of the study area, i.e., all the green spaces within, including private and public gardens, forests, golf courses and street trees, was strategically managed to serve the interests of the population, establishing a link between the urban environment and the surrounding natural environment through biophysical and social infrastructure [61], with the various environmental, ecological, social, economic and human well-being ecosystem services associated with them. The green infrastructure occupies about half of the total study area (320 ha) and it can be divided into: private green spaces (95%), public green spaces (4.8%) and ecological green spaces (0.2%). 84% of the public green spaces are irrigated, with a global water consumption of 41 245m³ [62], in 2024. Among the various measures implemented by local administration, the water management entity for Quinta do Lago, to reduce water consumption in green spaces, as part of the Contingency Plan for Drought in the Algarve, approved by the Council of Ministers in 2024 , the following stand out: the use of wastewater, with an expected 84% increase in its use for watering green spaces by 2025; renovation of the public water supply network; optimisation of smart irrigation systems; and conversion of public green spaces into xerophytic gardens, using native vegetation [62].

2.2. Data Sources and Research Tools

The aim of this literature review was to highlight the diverse ecological and aesthetic features of xerophytic vegetation, that allows them to be perfectly integrated into green spaces, in a context of limited water availability, using the principles and techniques of Xeriscape [63]. Throughout the research process, priority was given to studies and scientific literature developed in regions with similar climatic and bioclimatic characteristics to the Algarve. These studies investigated the ecological and socio-economic factors of green spaces and their adaptation and resilience to the recurring phenomenon of droughts. In addition, the identification of various species of native flora was undertaken in order to ascertain their applicability in urban green spaces and simultaneously promote their protection and conservation, given part of this vegetation has been threatened by growing anthropogenic pressures and climate change [64].

A set of specific methodologies were used, based on previous work, namely:

• Bioclimatic analysis - the reference methodology considered was the Bioclimatic Classification of the Earth, developed and updated by Rivas-Martínez ([16,39,40,41,42,43,44,45]) and Rivas-Martínez et al. ([42,46,47,48]), which is the reference methodology for the Iberian Peninsula, and also [65];
• Biogeographical analysis - based on the work carried out by [19,37,44,48];
• Description of Ecosystem Services in urban green spaces - mainly based on the work of [14,49];
• Climate diagnosis for the Mediterranean basin and the Algarve – based on the work carried out by [45];
• Climate change analysis - the data provided by the reports of IPCC [4,7,8,9,11,22,50,51,52,53,54];
• Hydric characterization, i.e., average consumption and actual water losses on a regional scale, analysed through the data provided by [67].

The review of 94 scientific publications, in English, was conducted across the Web of Science, Scopus and Springer databases, as well Google Scholar, academic repositories, as well as literature from national and online libraries (17). This review encompassed master’s theses and doctoral dissertations (5), as well as websites (3) on the subject in question and technical reports (27) from various international organisations, including: IPCC (Intergovernmental Panel on Climate Change), MedECC (Mediterranean Experts on Climate and Environmental Change), FAO (Food and Agriculture Organisation), WMO (World Meteorological Organisation), UNDP (United Nations Development Programme), UN (United Nations), EU (European Commission), WWF (World Wide Fund for Nature); and national ones such as: IPMA (Instituto Português do Mar e da Atmosfera), ERSAR (Entidade Reguladora dos Serviços de Águas e Resíduos), GPP (Gabinete de Planeamento, Políticas e Administração Geral), APA (Agência Portuguesa do Ambiente) and AMAL (Associação Intermunicipal do Algarve). The strategy used for this research involved the execution of advanced search in the databases, using keywords related to the theme and goals of this review. These keywords included, but were not limited to, the following: aridity, water scarcity, green spaces, Mediterranean flora, bioclimatic indices, green infrastructure, drought, ecosystem services, native vegetation, exotic vegetation, xerophytic vegetation and xericity.

Most of the consulted literature spans from 2000 to 2025, with the objective of incorporating recent studies. Since this is a theme, that has been the subject of few studies, it was necessary to consult older literature to consolidate certain concepts. Restrictions on geographical regions were applied to maintain an objective view of the research topic for arid Mediterranean areas.

After searching the database, the articles were imported into the bibliographic reference management software ZOTERO (Version 7.0.11 (64-bit), copyright 2006-2024, Zotero Developers, Virginia, USA). Subsequently, duplicates were removed, and the screening of article titles/summaries was carried out independently and in parallel by the first author, under the guidance of the other authors.

In order to make the text easier to read, the descriptors of all the species and genera mentioned in this article are included in Appendix A. The nomenclature adopted was based on [68]. However, due to subsequent updates, it was necessary to refer to other bibliographic references such as [69,70].

3. Xeric Environments and Xerophytic Vegetation

3.1. Edaphoclimatic Characterization of Xeric Environments

The density of vegetation plays a major role in these environments, because the microclimate created increases relative humidity, so the temperature is at least 10 ºC above atmospheric [71]. These thermal and hydrological features of the atmosphere determine the level of stress on the vegetation, whose physiological responses are manifold. In highly xeric environments, the interaction between intense radiation (above 1500µmol/m²) and high temperatures (above 40 ºC) intensifies the stress on vegetation [72], which is mitigated by the morphophysiological changes developed by this vegetation, such as: 1) high reflection coefficient, due to seasonal dimorphism, where the leaves are lighter in the dry season, due to the production of waxes, and darker in the wetter season; 2) change in the angle of the petiole to avoid direct radiation; 3) leaf abscission in the summer season; 4) succulence, which helps to control thermal stress, due to the high specific heat of the water inside the hydrenchyma.

In the case of dry ombrotype, where precipitation is low, soils are generally poorly developed, even if the original material has been exposed to the elements for a long period, as the action of biological and climatic factors is strongly limited [45]. Mediterranean soils are highly exposed to the precipitation regime of the cold season, which consequently increases erosion and reduces the organic matter layer of the topsoil, which is usually less than 5 % of the soil volume [73]. This organic matter is essential for providing nutrients to vegetation, but also for soil structure and moisture retention. In the Mediterranean climate, the soil moisture regime is classified as xeric. In this regime, most leaching processes occur in winter and early spring, when precipitation is high and evapotranspiration potential is low [74]. This regime is characterized by dry soil (with moisture levels retained at tensions above 15 atm) for at least 45 consecutive days within the four months following the summer solstice, in at least six years per decade, and by wet soil (with moisture levels maintained at tensions below 15 atm) for at least 45 consecutive days within the four months following the winter solstice, also in at least six years per decade [75]. Normally, since the majority of the annual precipitation rates in the southern part of the Algarve region are low (400–600 mm), complete leaching of soluble materials does not occur, leading to the accumulation of carbonates and other soluble salts. This can result in compacted and impermeable layers (petrocalcic horizons), that inhibit root development [76] and increases soil alkalinity, affecting nutrient uptake or even reducing their availability to plants [73].

According to Loidi (2017) vegetation series (or sigmeta) can be arranged in the zonation along the ridge-slope-piedmont-valley bottom model, that differentiated according to soil type [77]:

• Edaphoxerophilous, xerophytic vegetation that develops on soils such as leptosls, lithosols, arenosols, gypsisols, etc., characterized by water deficit, where the water received form precipitation is rapidly drained.
• Climatophilous, mesophtytic vegetation that develops on mature soils that only receive water only through precipitation.
• Temporihygrophilous, mesohygrophytic vegetation that grows only on soils that are wet or swampy for part of the year and well drained for the rest.
• Edaphohygrophilous, edaphohygrophilic vegetation that develops in hydromorphic conditions, such as permanently wet or swampy soils.

The characteristics of the soil will determine its capacity to store water from precipitation. In the case of sandy soils, soil moisture is low due to high drainage rates (≤30 mm/hour ) [78]. In the case of more compacted soils, such as clay soils, characterised by high water retention or soils with forming petrocalcic layers, infiltration is very low (1-5 mm/hour) [78] and does not reach the deeper layers of the soil [74]. And there is also the case of the absence of a soil layer, such as rocky subsoils, that is impermeable to water infiltration, and the vast majority of precipitation water runs off superficially.

Nutrients tend to accumulate in the topsoil layer (2–5 cm), especially under the canopy of shrubs. As a result, these “fertility islands” concentrate most of the fauna activity and water retention [21]. Low water availability in xeric environments, also influences nutrient uptake, leading to intensified nutrient deficiencies, mainly due to low soil nutrient availability [79]. Additionally, the nutrient storage capacity is influenced by solar radiation [80], as a higher availability of photosynthetically active radiation (PAR: 400–700 nm) [81] results in a higher capacity to synthesize photoassimilates. However, in arid-zone vegetation, this should not exceed 2000 µmol/m², as there is a risk of damage to photosynthetic tissues [72]. In CAM plants, the photoperiod, not only affects flowering of certain species, also affects CO₂ absorption. There is a trend toward greater accumulation under more intense and prolonged irradiance conditions, where temperatures range between 10 and 22°C [82].

In xeric environments, precipitation is generally sporadic and discontinuous, occurring in rainfall events that act stimulate the development of the biotic components of these systems [83]. Water availability for vegetation depends on three factors: relative humidity, precipitation index and soil characteristics. In arid environments, the average relative humidity ranges from 10–30%, while in semi-arid environments it is 20–30 % in the summer and 60–70 % in the rainy season, as observed in the Mediterranean climate [80]. Proximity to the ocean also promotes greater thermal regularisation compared to more continental areas [64].

Like temperature, relative humidity also varies significantly between day and night. At night, as temperatures drop, relative humidity increases and can reach 40–60 % as the air retains more moisture [71]. The dew formed in these conditions is an important source of water for some plant and animal species. There is also a positive correlation between humidity and proximity to the ocean, i.e., the closer to the ocean, the higher the relative humidity. This is because the oceans act as large masses of constantly evaporating water, which increases the relative humidity of the air, by releasing water vapour into the atmosphere [64].

3.2. Characterization of Xerophytic Vegetation

According to Rivas-Martínez (2007) the term xerophyte can be defined has “ having an affinity for dry environments or being able to live in climates with low precipitation. Plants or plant communities adapted to dry conditions, whether caused by climate or edaphic factors.” [16]. In the Mediterranean Basin, there are two general types of xericity: Mesoxericity, which is predominantly located in the northern part of the basin (Southern Europe), where the study area, of this research is located, and it is characterized by the presence of Mediterranean flora; and Hyperxericity, which is mostly located in the southern part of the basin (North Africa) and is characterized by succulent plants [16].

Based on the type of adaptation to xericity, xerophyte species can be grouped into the following categories [76]:

• Arid-passive species – species whose photosynthetic tissues remain inactive during the summer months. In the case of annuals, the challenge posed by xericity is surmounted through the synchronisation of their life cycle with periods of increased precipitation. During the hot and dry season, the plant survives in the form of bulbs or seeds, germinating only when conditions become favourable, as in the case of subterranean clover (e.g., Lupinus cosentinii). Perennial species, on the other hand, may undergo a deciduous phase during the summer months, thereby reallocating their reserves to underground organs until the subsequent wet season (e.g., Prunus dulcis). Certain species have persistent sclerophyllous foliage, which plays a crucial role in regulating transpiration rates during the hot season (e.g., Quercus rotundifolia);
• Arid-active species – species with tissues adapted for water storage, such as succulents. These species accumulate water in their tissues during periods of sufficient moisture and subsequently utilize this water reserve during the arid season, when they exhibit reduced metabolic rates and maintain their biomass.

Significant climate changes occurred in the Mediterranean region approximately 3.2 million years ago, during the Pliocene period [84], gradually establishing the current climatic patterns of the Mediterranean [50] (Figure 5), marked by a wide variety of biomes, depending on precipitation levels, ranging from dense evergreen or deciduous forests to open woodlands, shrublands, semi-deserts, deserts, and hyper-deserts [45]. The climate shifts and the recurrent wildfires [17] in the Mediterranean region are believed to have driven the evolution of Mediterranean flora, promoting the development numerous adaptive mechanisms to withstand prolonged drought, natural disturbances such as wildfires [18], and human-induced disturbances [85]. For the fire-adaptive strategies, stands out: the thick bark layers that protect the trunk from biotic and abiotic factors, containing suberin, a hydrophobic polymer (e.g., Quercus spp.) [86]; the vegetative regeneration through underground stems (lignotubers), as seen in Pistacia lentiscus and kermes oak Quercus coccifera [87]; the germination triggered by heat, as seen in species with large soil seed banks (e.g., Cistus spp.); the development of volatile oils in species like Thymus spp. and Rosmarinus spp., which increase flammability in their surroundings, allowing for faster post-fire regeneration, due to reduced competition [85]. As for the for the climate shifts, they played a crucial role in species richness and the resilience of Mediterranean ecosystems, characterized by drought-resistance adaptations as small, persistent, sclerophyllous leaves, which are highly aromatic and covered with epicuticular waxes, reducing excessive water loss through transpiration [43] and deep and extensive root systems, which sustain regrowth after the destruction of the aerial part of the plant [17]. Thus, the study area of this research is, as the Mediterranean region, shaped by drought and fire.

On the other hand, succulents are highly specialized plants whose ability to store large volumes of water is essential for their survival in highly unfavourable conditions [20]. Currently, approximately 20 000 species of succulents are known, distributed across 60 botanical families [88], representing 3–5 % of all angiosperms [89]. Around 5–10 million years ago, significant environmental changes, such as temperature drops, increased aridity, and a decrease in atmospheric CO₂ concentration, led to an intense process of speciation. This promoted the rapid colonization of arid environments and drove the development of adaptive structures to withstand low water availability [90].

Figure 5. Global occurrence of the Mediterranean Macrobioclimate in nine biogeographical regions: Mediterranean Basin, Irano-Turanian, Saharan-North Arabian, California, Great Basin, Rocky Mountains, Middle Chilean-Patagonian, Capensic, and Southwestern Australia, according to the Bioclimatic Classification of the Earth, developed by Rivas-Martínez. Source: [45,50].

Figure 5. Global occurrence of the Mediterranean Macrobioclimate in nine biogeographical regions: Mediterranean Basin, Irano-Turanian, Saharan-North Arabian, California, Great Basin, Rocky Mountains, Middle Chilean-Patagonian, Capensic, and Southwestern Australia, according to the Bioclimatic Classification of the Earth, developed by Rivas-Martínez. Source: [45,50].

Among these adaptive features, the most notable is succulence, the ability to store water in specialized tissues (hydrenchyma cells), which can be gradually used during dry periods [89]. To be considered a succulent, a species must exhibit the following attributes [89]:

• Succulence, i.e., the ability to store water in hydrenchyma cells, predominantly in thick, fleshy leaves and stems, which can reach 90–95 % water content.
• Epidermal appendages, such as waxes and trichomes (e.g., Kalanchoe spp.), which can significantly reduce water loss through transpiration.
• Low surface-area-to-volume ratio (SA:V), that means small, fleshy leaves, as seen in Echeveria, which are less prone to water losses. This also includes leaf modifications like spines in cacti, which reduce losses by transpiration.
• CAM photosynthesis, is a physiological adaptation mechanism, where the Calvin Cycle is carried out at different times. In this photosynthetic mechanism, the stomata only open during the night, absorbing CO₂, which is then stored during the night and only transformed into sugars during the day, with radiation. Thus, by opening the stomata only at night, when the temperature is lower and the relative humidity higher, excessive water loss through transpiration are significantly reduced [91].
• High capacity for asexual reproduction, mainly through leaf cuttings or stem segments.
• High thermal capacity, allowing the plant to gradually release stored heat at night, protecting tissues from low nocturnal temperatures.Parte inferior do formulário

Although water consumption varies between xerophytic species, it can represent a reduction of up to 80 % compared to mesophytic plants, due to the various adaptation mechanisms xerophytes have to cope with drought [92]. It can reduce transpiration losses by up to 5-10 times compared to mesophytic species, especially if we consider the use of water in CAM photosynthesis [92].

3.3. Xerophytic Vegetation in Urban Green Spaces

The contemporary urban model is characterized by pollution, soil degradation, rapid population growth, and accelerated depletion of natural resources [93]. Regarding biodiversity, the main impacts are land-use changes linked to urban infrastructure expansion [94]. For plant species, these disturbances leads to habitat homogenization, reducing species diversity, as less resilient species tend to disappear [95]. Additionally, this homogenization facilitates the spread of exotic species, often invasive ones [96]. Although the Mediterranean Basin shows some resilience to the invasion of exotic species, there has been a gradual increase in recent years [23], particularly from invasive species originating in other Mediterranean climatic regions and from xeric and temperate regions, facilitated by climatic convergence [97]. These species pose a serious threat to the stability of biodiversity and ecosystems, but also have significant socioeconomic impacts, with losses exceeding 12.5 billion €/year in Europe alone [24]. Currently, climate change is one of the main drivers of exotic species invasions in the Mediterranean region, as levels of aridity and temperature are rising. According to a study conducted by Gritti et al. (2006) [26], there is a progressive trend of replacement of trees by species better adapted to the new climatic conditions, with faster establishment and growth rates.

Thus, the sustainable development of a city must be based on the promotion of ecosystem services, i.e., a set of ecological, social, economic and cultural benefits provided by nature, that directly or indirectly promote the quality of life and well-being of the population [11]. With the new climate paradigm [19], ecosystem services are gaining new importance, as the resilience of urban environments to climate change depends on the valuation of these types of services [98]. In addition, it is necessary to consider the impact of climate change at the bioclimatological level, as data suggests that there has been a shift in vegetation, especially at low altitudes, from 150 to 300 m (the boundary between the Mediterranean and temperate climates), with an increase in drought-adapted species at low altitudes [99].

Green spaces have always been part of society’s daily life [100], but they gained particular prominence in the 18th century with industrialisation, which led to an increase in urbanisation, whose disorderly growth resulted in serious pollution and public health problems [95]. Since then, these spaces have proliferated in urban environments, albeit under constant pressure due from increased urbanisation, although their benefits are now recognised as a key element in mitigating the effects of climate change [101]. In urban environments, green spaces provide three categories of benefits [102]:

• Environmental and ecological benefits – related to urban resilience, in the context of adaptation to climate change (e.g., air purification, management of stormwater runoff and improvement of water quality, carbon sequestration, climate regulation and biodiversity promotion [98],[103] [104];
• Social and human health benefits – related to the aesthetic, recreational, educational and human health values provided by vegetation (e.g., beauty derived from the visual impact of green spaces, physical and mental well-being, the promotion of social relationships and environmental awareness [95];
• Economic benefits – related to energy efficiency and reduced dependence on artificial climatization (e.g., tourism, as a leisure or recreational attraction, and property valuation [98]).

Urban green spaces are part of the Green Infrastructure, which is an integrated and coherent system of multifunctional green areas, strategically managed to serve the interests of the population, linking the urban and rural environments through biophysical and social infrastructures [61] while providing various ecosystem services. Green Infrastructure is part of a more holistic system, the Urban Ecological Structure, i.e., the set of natural and semi-natural components in urban and peripheral areas, whose interactions aim to promote and conserve biodiversity by maintaining and protecting ecological and environmental processes and promoting the sustainable use of natural resources in order to mitigate the impacts of anthropogenic activities [105]. Private gardens, often associated with the tourism sector in the Algarve region, as an integral component of the urban Green Infrastructure, play an important role in the resilience of the urban environment to climate change, as they represent between 22 % and 36 % [106] of green areas in low-density urban environments, depending on the location and length of the city’s existence [107].

In fact, in the Mediterranean region, the impact of this water consumption on this increasingly scarce resource is quite significant [19], and can be 2.5-4.5 times greater for houses without green spaces [108]. Given the heterogeneity of these spaces, the environmental impact is also variable [109], being higher with a greater use of vegetation with high water consumption and maintenance, such as perennial grasslands [110].

There are two main direct impacts of climate change on the urban environment: increases in temperature and changes in the dynamics of the hydrological cycle [111]. The rise in temperature resulting from climate change [19] will aggravate the urban ‘heat island’ effect, i.e., the increase in average temperature in urban areas due to the specific characteristics of built and impermeable areas, which alter the thermal balance [112], inducing heat dispersion [113]. In arid climates, this temperature range can exceed 10 ºC [114].

As for changes in the dynamics of the hydrological cycle, the main threats are droughts, caused by increasingly unpredictable rainfall patterns, and floods, caused by occasional but intense precipitation [111]. In general, today’s urban landscape are not very resilient to climate change, as they have a large amount of impermeable areas, which contribute to an increase in the likelihood of flooding, pollution of water lines, loss of natural habitats, interference with the natural recharge of aquifers, an increase in the costs associated with rainwater drainage infrastructures and the non-utilisation of the resources resulting from this capture, and an increase in the ‘heat island’ effect [115].

In order to achieve the sustainability and liveability of future cities [116], but also to mitigate the impacts of climate change, that are already being felt, it is necessary to adapt current consolidated areas and to rethink new urban growth spaces, using Nature Based Solutions (NBS) (e.g., green roofs, rain gardens, retention basins, green corridors, reforestation with native species, urban gardens, parks, etc. ), defined by the European Commission as: “(…) nature-inspired and nature-supported solutions that are economically viable, provide environmental, social and economic benefits and contributes to increased resilience; these solutions bring a greater and more diverse number of natural and nature-based features and processes to cities, land and seascapes through locally adapted, resource-efficient and systemic interventions” [117]. This type of solution is an effective tool against climate change in the urban environment, but also in terms of improving human well-being [12] and economically, as it costs less than conventional solutions that involve building infrastructure [117].

Urban vegetation plays a key role in mitigating the main risk factors in urban environments exacerbated by climate change, namely the ‘heat island’ [113] and changes in the dynamics of the hydrological cycle [111], while also providing numerous ecosystem services [118]. Vegetation can play an important role in the climatic comfort of urban areas, as the temperature range between green areas and artificial surfaces in buildings an pavement areas can be 11 ºC to 25 ºC lower [119], contributing to greater energy efficiency of the buildings, reducing air and noise pollution, sequestering carbon, promoting biodiversity, among other ecosystem services [118]. In addition, the vegetation cover also has the capacity to slow down the surface runoff of rainwater, which contributes to the phenomenon of flash floods, especially in the Mediterranean region characterised by rainfall instability [19], but also to promote the infiltration of water into the soil, contributing to the recharge of groundwater bodies [111]. According to [15], green roofs with xerophytic vegetation have been shown to reduce surface runoff by up to 50 % during intense rainfall events, thus contributing to the mitigation of flooding in urban environments, while at the same time reducing the need for irrigation due to their adaptation to drought conditions.

In the specific case of the Mediterranean region, which is characterised by well-defined dry and wet periods [45], large green areas with only herbaceous vegetation should be avoided, as they do not produce significant effects in terms of mitigating air temperature, in addition to higher maintenance costs and greater water consumption [14]. Water availability is an extremely important factor in this bioclimatic region, so it is necessary to strike a balance between the application of tree-sized vegetation with a high evaporative cooling capacity and medium/low xerophytic vegetation, which significantly reduces the water requirements of these green spaces [120].

In general, the literature suggests that urban cooling in arid climates should be based on a vegetation strategy that minimises water use, especially using tree and shrub species that promote shading [13]. Although the literature suggests that lawns are effective in urban cooling, mainly due to their high evaporative cooling capacity, in arid climates this benefit is offset out by the high water demand, a limiting resource in these regions [121].

4. Drought in the Mediterranean and Study Area Context

According to the UN (United Nations) Convention to Combat Desertification (UNCCD), as well from the European Environment agency (EEA), drought can be understood as a “naturally occurring phenomenon that exists when precipitation has been significantly below normal recorded levels, causing serious hydrological imbalances that adversely affect land resource production systems” [122]. The severity of this climatic phenomenon varies depending on the region where it occurs, being more or less intense based on the duration of the period of reduced precipitation and the extent of deviation from the climatic norm, but also depending on the demand for water resources for various anthropogenic activities [123]. Drought differs from other extreme climatic phenomena in that it is a slower process, whose impacts are not immediate [2]. Although they may be understood as similar concepts, drought and water scarcity have different meanings. Water scarcity is considered to occur when the water resources of a given region are insufficient to meet water use needs [124].

Depending on the perspective from which drought is assessed, five types of drought can be considered:

• Meteorological drought is associated with a lack of precipitation. It is intrinsically related to the regional conditions, as it depends on factors such as wind speed, temperature, relative humidity and solar radiation. It is defined as the measure of deviation in precipitation relative to the climatic norm [125];
• Agricultural drought results from an imbalance between the water available in the soil, the water needs of crops and evapotranspiration [125]. According to Kulik (1962), periods of agricultural drought are considered to occur when only 19 mm of water is available in the topsoil layer (0.20m) [126]. When only 9 mm is available, a situation of severe agricultural drought is considered [123], typically lasting between 3 and 9 months [127];
• Agrometeorological drought results from the combination of meteorological and agricultural drought, i.e., drought induced by an imbalance between the water available in the soil, the water needs of crops, and their transpiration rates [125];
• Hydrological drought is related to the reduction of surface and groundwater storage [125]. Typically, this type of drought does not occur at the same time as meteorological drought, as the effects of low precipitation are not immediately apparent [1]. It occurs later and usually lasts for periods longer than 9 months [127];
• Socioeconomic drought occurs when the availability of water is so restricted that it begins to have a negative impact on economic activities.

In May 2024, according to data from the report of the Permanent Commission for Drought Prevention, Monitoring, and Follow-up, the Council of Ministers decided by Resolution no. 26-A/2024 of 20 February, that the Algarve river basins were in a situation of severe hydrological drought, making it impossible to extract water for irrigation, thus affecting regional socioeconomic activities, transforming in a socioeconomic drought situation as well, with restrictions of water use by the population [128].

4.1. Drought in the Mediterranean Basin

Currently, the Mediterranean region is home to over 500 million people [4], placing significant pressure on increasingly scarce water resources due to the effects of climate change [19]. Among these, 180 million people, particularly in the southern and eastern parts of the Mediterranean basin, suffer from water scarcity [4]. In this region, agriculture is the main water-consuming sector, accounting for 64-69 % [4]of total water consumption and irrigating 25 % of the region’s total area, with a tendency for this area to increase [4]. Moreover, this pressure is exacerbated by the fact that Mediterranean countries are among the top tourist destinations in Europe, especially during the summer season, when irrigation needs are also at their peak. This contributes not only to the rapid depletion of water resources but also to increased socio-economic risks. Although drought is a recurring phenomenon in the Mediterranean basin, these countries have some of the highest water consumption rates (Figure 5). This is explained not only by the agricultural and tourism pressure on resources but also by the inefficiency and high levels of waste in public water supply networks and irrigation systems [3].

Figure 5. Water withdrawal per capita (m³/inhabitant/year) in Mediterranean European countries in 2021, with Greece, Spain, and Portugal standing out for the highest consumption. Source: [5].

Figure 5. Water withdrawal per capita (m³/inhabitant/year) in Mediterranean European countries in 2021, with Greece, Spain, and Portugal standing out for the highest consumption. Source: [5].

Greece, Spain, and Portugal are the countries with the highest water withdrawals per capita, specifically at 956.69, 611.12, and 596 m³ per inhabitant per year, respectively, significantly above the European average of 381.54 m³ per inhabitant per year. Furthermore, these countries have some of the lowest levels of water use efficiency (Figure 6), significantly below the European average (64.33 US$/m³), mainly due to inefficiencies in agriculture and public supply networks. These figures illustrate that in the regions where sustainable water resource management is most urgently needed, water use efficient strategies are failing or simply inadequate. In a scenario of intensifying drought periods, this could result in severe economic losses.

According to the Climate Change 2023 report by the IPCC (Intergovernmental Panel on Climate Change) [19], the Mediterranean basin, which includes southern Portugal, is particularly vulnerable to climate change, with negative consequences for water resources, ecosystems, economic activities, and society. The fact that this region lies in a transition zone between the arid climate of North Africa and the temperate and cold climates of higher latitudes in Central Europe means that even small climate variations have a significant impact on the Mediterranean climate [129]. This increases its vulnerability to climate change, making extreme weather events such as droughts and heatwaves 5 to 10 times more frequent and severe [4]. The combination of these geographical and atmospheric factors makes the Mediterranean region a hotspot for climate change, worsening its environmental and economic repercussions. Portugal, in particular, is the second country in the Eurozone whose banking sector is most exposed to climate change risks [19]. According to data from the World Meteorological Organization (WMO), the Mediterranean basin is warming 20 % faster than the global average [130] and 50 % faster in summer, with an average air temperature increase of 1.54 °C compared to pre-industrial levels [130].

4.2. Drought in the Algarve Region and Study Area

Drought has become more pronounced in certain regions of mainland Portugal, particularly in the Algarve. These irregular precipitation patterns have become more pronounced since the year 2000 [131] (Figure 7), with an increasing number of severe drought episodes, more precisely 17 episodes between the years 2000 and 2023 [7]. Drought indices have also become more pronounced in recent decades, with a greater frequency of severe drought events [132], especially in the most southern part of the Algarve region. Currently, the Algarve has recorded a 25% decrease in precipitation, causing a scenario of meteorological drought, and according to the IPCC RCP8.5 scenario, this situation is expected to worsen, with an anticipated 40% reduction in annual precipitation [7]. Specifically for the study area, when comparing the climatological norms for 1971–2000, 1981–2010, and 1991–2020 (Figure 8), there is a clear decrease in precipitation of 56.4 mm between 1981 and 2020 and an increase of 0.8ºC in temperature between 1971 and 2020 [133,134,135], facts that highlight the increase in aridity driven by climate change [19].

This region, has an annual water demand of 75 million m³ [67]. However, in 2022, 15 million m³ of this total was lost—an amount that could have covered 49% of the region’s urban water demand, which is further exacerbated by tourism. Additionally, out of the 75 million m³, 40 million m³ are directed to wastewater treatment plants [67]. This means that 55 million m³ of water, that could be used for purposes such as irrigation of green spaces or agricultural crops, is simply wasted, reflecting a serious mismanagement of an increasingly scarce resource in the region. However, efforts have been made towards more efficient water management through the National Strategy for Water Management – Water tha Unites, which includes a set of measures aimed at improving efficiency, resilience and intelligence in water management [136].

The intensification of drought in the Algarve reflects the reality seen throughout the Mediterranean basin, driven by climate change [19]. Drought poses as a serious threat to the socio-economic development of the Algarve, with multi-sectoral impacts [137], but also ecological consequences, jeopardizing the survival of plant communities, especially those that are more vulnerable, such as temporary ponds [138] or the relict vegetation associated with the top of Monchique [139] . According to the GPP’s latest Monitoring, Agrometeorological, and Hydrological Report for 2023 [128], the Algarve is one of the regions most affected by drought, impacting both reservoir storage levels and groundwater. As of today, the Ribeiras do Algarve basin (Barlavento) is experiencing Extreme Hydrological Drought, while the Guadiana basin (Sotavento) is under Moderate Hydrological Drought [128].

The Algarve is divided into two hydrographic basins: The Guadiana basin (Sotavento – East side of Algarve) 93 % of water consumption is for agriculture, followed by 6 % for urban use and 1 % for industry [140]. In the Ribeiras do Algarve basin (Barlavento – West side of Algarve) 67 % of water is used for agriculture, followed by 22 % for urban use and 7 % for tourism [140]. In terms of water use efficiency, losses in the urban sector are significant, exceeding 40 % in certain Algarve municipalities [67] . Additionally, losses in agriculture reach 37.5 %, and in industry, 22.5% [141]. These real water losses translate into high economic costs, estimated at €86.3 million per year (average from 2018-2024), according to the latest Annual Report on Water and Waste Services in Portugal [67].

Official data indicates that 67 % of Algarve’s water comes from groundwater and 33% from reservoirs. The main water-consuming sectors are: Agriculture: 56.8 %, Urban use 34% and Golf courses 6.4 % [57]. From the total urban water volume, 11% is allocated to green spaces, with 4.88 hm³/year for public areas (excluding golf courses) and 3.91 hm³/year for private spaces [57], with the highest consumption in the coastal municipalities (Figure 9), where tourism is more intense, closely associated with the Sun and Sea offer [137]. The high consumption in the municipality of Loulé is mainly associated with the tourism developments of Vale do Lobo, Quinta do Lago and Vilamoura, whose consumption is 0.35, 0.34 and 0.57 hm³/year respectively. Considering that these tourism developments are located in a dry ombrotype characterized by low precipitation rates [52], this highlights the importance of sustainable water management, adapted to the new climatic reality, which can be achieved by using xerophytic vegetation with low water requirements.

5. How to Address the Drought Challenges in the Study Area

Considering that the Mediterranean basin is a climate change hotspot, i.e., a region particularly vulnerable to the impacts of global warming due to a combination of geographical, climatic and socio-economic factors [4], a new sustainable approach to water resource management in the region, which includes this research study area, will be crucial to address the effects of water scarcity and prolonged droughts across different sectors. In the particular case of this research, in the context of Quinta do Lago green spaces, particularly associated with a key sector in the Algarve, the tourism, the use of xerophytic vegetation is proposed as a way of adapting these territories, rather than the current landscaping model that favours exotic vegetation [20], whose water consumption high rates is incompatible with the current climate situation and climate projections for the region [108].

In the Algarve, besides the decrease of precipitation patterns [49], resulting from climate change, water scarcity is essentially linked to two issues [137]: tourism and the region’s water supply infrastructure. As a socio-economic activity, tourism is highly dependent on water resources, as it is intrinsically linked to leisure and sport green spaces. Considering that tourism activity in the region is expected to increase by approximately 9% by 2025 [8], it is expected that green spaces, especially private green spaces, and golf courses will also increase, making it urgent to reformulate current landscaping practices, towards water consumption sustainability. Unlike the remaining areas of Algarve where the average of water losses is 30% [67], mainly due to obsolete and degraded supply systems, the study area’s water supply network is the most efficient in the country, with losses that do not go over 2.8% [67]. However, the daily water consumption per inhabitant is the significantly higher (1093L/inhabitant) than the national average (184L/inhabitant), mostly due to the large domestic green space areas, with a total volume of 251 156 m³ of water for its irrigation green, in 2024 [62].

Despite the water supply system efficiency in the study area, there are several issues that explain the use of large volumes of public water, in its green spaces, mostly the private ones. The first issue concerns the widespread use of exotic vegetation with high water requirements, which is very common in landscaping practices in the area. Although the Quinta do Lago Urbanisation Plan clearly states that green space projects must incorporate native flora, due to its obvious edaphoclimatic advantages, and that lawn areas must not exceed 30% of the total green space area [55], this has not been the case in recent decades, highlighting a clear failure to enforce this legislation. Furthermore, the use of exotic vegetation poses other problems, such as the introduction of invasive species, such as Carpobrotus edulis or Acacia sp., with serious implications for biodiversity [142].

Generally, the reasons that lead to the choice of exotic vegetation, in the study area, over native vegetation are related to aesthetic considerations, socioeconomic factors, limited knowledge of the ornamental value the native vegetation and its impact on local biodiversity [13], and particularly its availability in nurseries. In practical terms, the availability in nurseries greatly influences how the Landscape Architects operate, since there is not a wide range of Mediterranean species available, largely due to the factors previously described [13]. Additionally, the lack of knowledge about the ornamental features of xerophytic vegetation and the nationality of residents, both permanent and seasonal, mainly from northern and central Europe [143], also has implications for the green space projects implemented in this area, as this population wishes to recreate the permanently green landscapes, typical of their country of origin.

To understand the ornamental potential of natural xerophytic species in green spaces, it is necessary to know its biogeographic features, because these species are adapted to the edaphoclimatic conditions of the site, use water more efficiently, they are more resilient to plagues and diseases and knowing this helps prevent the introduction of alien species [45]. Considering the works of [43,50,64,144], a group of species, typically associated with xeric or dry environments, were selected from the biogeographic Algarve and Monchique Sector, Algarve District (50a), where the study area of this research takes place. These species can colonise biotopes with high edaphic or ombroclimatic dryness, particularly associated with dry to subhumid ombroclimate or sandy or lithosols, like the ones that occur in the study area, as well as rocky surfaces (Appendix B).

Approximately 70 % of the water consumed in a single-family home, with a garden, is used to irrigate this space [25], highlighting the need to reduce this consumption through sustainable landscaping practices, which should include the installation of high efficient irrigation systems, but also the selection of appropriate vegetation with low water requirements [20], prioritizing native vegetation. According to bibliography, a xeric green space con pose significant reductions in water consumptions, between 40 and 50% [63,145]. Thus, a significant decrease of the volume of irrigation water is possible with xerophytic vegetation. But, as seen before, because the study area is in a Mediterranean region it is also important to find the balance between water management and the cooling effect of vegetation, in order to lower the temperature, using different strata of vegetation.

In the study area, efforts have been made to decrease the volume of water in green spaces. With the Algarve experiencing periods of severe and prolonged drought, and the activation of the Contingency Plan for Drought in the Algarve [146], in 2024 , the local administration, has adopted a series of measures to achieve the imposed 15% cuts in water consumption, through strategies such as reducing water pressure in the network, prohibiting the watering of public and private green spaces with water from the public supply system, implementing water efficiency measures in tourist developments, and prohibiting the watering of golf courses with water from the public supply network. These strategies translated into measures that included the renovation of the public water supply network, the expansion of the rainwater and wastewater supply network for irrigation, detection and reduction of undue inflows, optimisation of smart irrigation systems and redevelopment of public green spaces into xerophytic gardens using native vegetation, with average decreases in water consumption from 10 m³/month to 4.8 m³/month in these specific cases, corresponding to a decrease of approximately 108%, and in the other conversion, the average decreases in water consumption from 41 m³/month to 20 m3/month, corresponding to a decrease of approximately 105% [62].

6. Conclusions

Taking into account the edaphoclimatic features of the study area, particularly the water resources, it is clear that its green spaces need to be adapted, something that should be replicated throughout the remaining region of Litoral Algarve, where characteristics are similar, favouring the use of native xerophytic vegetation over the current predominance of exotic vegetation, whose water consumption and maintenance requirements are currently incompatible with the regional climatic realities. The careful selection of vegetation adapted to local soil and climatic conditions is fundamental to the sustainability of green spaces. The selection of a xerophytic floral composition is essential to simultaneously create aesthetically appealing spaces with low water consumption, that in the study are reached the decreases of 108%.

Tourism is an economic activity that is highly dependent on water resources and is strongly related to the study areas green spaces, mostly associated to private residences and golf courses, that bring economic benefits and value to the area. However, in this area these spaces are currently dominated by exotic species that consume a large volumes of water, making it necessary to promote the use of xerophytic vegetation, as a way of changing the current landscape model, since they offer significant advantages in terms of sustainability, water efficiency, ecological integration and aesthetics.

However, the design or conversion of green spaces with xerophytic vegetation must follow some criteria. The cultural context, the aesthetic preferences of each individual and the local conditions are the main factors that influence public opinion on this type of green space, and its acceptance is greater when the community is educated about its benefits. Furthermore, when designing these spaces it is necessary to combine different strata of xerophytic vegetation to achieve a balance between thermal comfort and water consumption in regions marked by periods of aridity.

The issue of water scarcity is a multifaceted problem in the study area, so a holistic approach must be adopted. For this reason, in addition to this literature review and characterisation of the study area, this research will proceed to obtain rigorous scientific data through population surveys and experimental trials with pre-selected species in the next phase of this research. This will allow understanding of the population’s perception of water scarcity, which may later prove to be a valuable tool for the competent authorities in mitigating the negative effects of drought on green spaces in the study area, but also in other similar areas in the Algarve and the Mediterranean basin, and will make it possible to have solid scientific information about the best adapted xerophytic species to use in the area green spaces, through data such as water consumption rates, temperature, radiation and nutrition levels, resulting from experimental trials.

An effective response to these challenges should aim not only to mitigate the effects of water scarcity on green spaces, but also to adopt long-term management models that guarantee their sustainability. Greater coordination between water management entities and national and regional water resource management policies is essential, with greater monitoring, licensing and inspection throughout the study area. However the lack of in-depth studies on the impacts of xerophytic vegetation on water resources and on the adaptation and resilience of green spaces in Mediterranean regions, marked by scenarios of water scarcity such as the study area, represents an additional challenge for the scientific community, in order to provide solid solutions to this issue.