Greening Schools for Climate Resilience and Sustainable Co-Design: A Case Study of Thermal Comfort in Coimbra, Portugal

Abstract

Urban school environments often face significant thermal discomfort due to extensive paved surfaces, limited vegetation, and outdated building designs. This study examines how green spaces can mitigate temperature extremes and improve thermal comfort at two secondary schools in Coimbra, Portugal: Escola Secundária José Falcão (ESJF) and Escola Secundária D. Dinis (ESDD). Using a mixed-methods approach that combined school community surveys with on-site microclimatic measurements, we integrated user feedback on comfort with data on temperature and humidity variations across different indoor and outdoor spaces. Results revealed that tree-shaded areas consistently maintained lower air temperatures and higher relative humidity than unshaded zones, which experienced intense heat accumulation—up to a 5 °C difference. At ESJF, the older infrastructure and large asphalt surfaces led to severe heat retention, with east-facing classrooms recording the highest indoor temperatures. ESDD’s pavilion-style layout and existing green spaces provided comparatively better thermal conditions, although insufficient vegetation maintenance and limited shade reduced their effectiveness. The findings demonstrate a clear correspondence between the school community’s perceptions of thermal comfort and the measured microclimatic data. Vegetation—particularly deciduous trees—plays a critical role in cooling the school microclimate through shading and evapotranspiration. Strategic interventions such as expanding tree cover in high-exposure areas, installing green roofs and walls, and carefully selecting species can significantly reduce temperature extremes and improve outdoor usability. In addition, fostering environmental education and participatory co-design programs can encourage sustainable behaviors within the school community, underlining the importance of inclusive, nature-based solutions for climate adaptation. This research highlights that integrating green infrastructure in school design and management is a cost-effective strategy for thermal regulation. Green spaces, when co-designed with community involvement, not only enhance climate resilience and student well-being but also contribute to broader sustainable urban development goals.

1. Introduction

Outdoor thermal conditions in schools and other public spaces have a direct impact on user comfort and well-being, particularly in Mediterranean climates characterized by hot, dry summers [1,2]. With climate change increasing the frequency of extreme heat events, concerns about urban heat islands and thermal stress in cities have grown [3,4,5]. Prolonged solar exposure [3], high CO₂ emissions [4], and heat-retentive urban materials (e.g., dark asphalt) further exacerbate these challenges, underscoring the need for effective mitigation strategies.

Vegetation, through shading and evapotranspiration, is among the most effective passive cooling solutions [6,7]. Trees can reduce ambient air temperatures by up to ~3 °C through evapotranspiration and even more through direct shade provision [8,9]. The magnitude of cooling, however, varies by species and canopy characteristics, requiring careful selection and placement of trees. In Mediterranean climates, deciduous trees offer dual advantages: in winter their bare canopies allow sunlight to warm surfaces, while in summer their foliage provides critical shade [8]. Evergreen species, although valuable for year-round shade and carbon sequestration, can sometimes create “hot shade” pockets if their canopy is sparse or heat is trapped beneath [9], highlighting the importance of species adaptability and canopy density for effective cooling.

The lack of green infrastructure planning in 20th-century public spaces is particularly relevant for urban educational facilities, which, in Portugal and elsewhere, often suffer from infrastructural inadequacies that impair thermal comfort [10]. In Portugal, historical underinvestment in school infrastructure and the rapid expansion of school construction in the late 20th century [11] resulted in many campuses with poor building insulation and barren outdoor yards. Despite recent modernization efforts (e.g., the Parque Escolar program), many schools still lack climate-sensitive design, with large unshaded paved areas contributing to heat stress [2].

Integrating green spaces into these environments could mitigate extreme temperatures while also providing psychological and social benefits [12]. A growing body of literature links greener schoolyards to improved student outcomes, including better academic performance [13,14,15,16], reduced stress levels [17,18], and enhanced mental health and attention [19,20]. Similar findings have been reported on university campuses around the world, where access to vegetation and shaded areas improves well-being and cognitive function [20,21,22].

In this context, our study evaluates outdoor thermal conditions at two secondary schools in Coimbra, Portugal, by combining microclimatic measurements collected during the warm season of 2024 with the perceptions of the school communities. The aim is to identify sources of thermal discomfort and to inform climate-resilient, co-created design strategies for school environments. By involving users in the assessment and focusing on nature-based solutions, we seek to demonstrate how the sustainable co-design of green infrastructure can enhance both thermal comfort and resilience in educational spaces.

2. Geographical Context and Study Sites

Coimbra is located in central coastal Portugal, at the transition between the coastal plain and the inland hilly region (Figure 1a,b). The local climate is Mediterranean with Atlantic influences [1], characterized by hot, dry summers and cool, rainy winters. Heatwaves and cold-air outbreaks occur periodically, contributing to significant seasonal thermal stress. Within the city, densely built-up areas tend to experience urban heat island effects, whereas parks and wooded areas provide cooler microclimates [4].

Escola Secundária José Falcão (ESJF) is a secondary school situated on the eastern slope of a small urban valley in central Coimbra, near the historic Jardim da Sereia park (Figure 1d,f). Designed by architects Carlos Ramos, Jorge Segurado, and Adelino Nunes and completed in 1936, its architecture reflects modernist Plano dos Liceus ideals from Portugal’s Estado Novo era [23,24]. The campus is terraced along the hillside, featuring a central quadrangular courtyard (with a few trees) enclosed by classroom buildings. Covered external corridors link this main block to a smaller secondary building housing the gymnasium, cafeteria, and support facilities. Outdoor spaces at ESJF include a large asphalt-paved yard on the upper terrace (eastern side) used for sports and leisure. Although two grassy areas with trees exist at the site’s periphery, access to these green spaces is restricted for most of the school community. As a result, students congregate mainly in the most arid, unshaded parts of the grounds. The only widely accessible vegetated area is a small grove of linden (Tilia spp.) trees at the lower east edge, which provides limited shade (Figure 1f).

Escola Secundária D. Dinis (ESDD) is a secondary school located in Coimbra’s urban periphery, within an industrial zone on the city’s outskirts. Built in 1985, the school comprises six low-rise classroom buildings (Buildings A–F, mostly two-story) connected by open-air covered walkways, plus a separate sports pavilion (Figure 1c,e). This pavilion-style layout, common in Portuguese schools of the 1980s, spreads the campus over a larger area. ESDD’s schoolyard includes both paved sports courts and an unpaved dirt field. In contrast to ESJF, ESDD is surrounded by relatively extensive green space: lawns and clusters of trees line much of the campus perimeter, and all these areas are fully accessible to students and staff. The tree canopy around ESDD consists mainly of maritime pines (Pinus pinaster) and Italian cypresses (Cupressus sempervirens), especially near the sports fields and along the western and northwestern boundaries of the grounds.

The two schools were selected for their contrasting geographical contexts, building typologies, and types of greenery, which together exemplify common conditions in Portuguese secondary schools. ESJF, located in central Coimbra, is embedded in dense historic urban fabric with 20th-century terraced buildings and limited accessible gardens, illustrating the constraints of retrofitting greenery in older urban sites. ESDD, in a suburban peripheral area, features a pavilion-style layout surrounded by extensive but often underutilized vegetation, reflecting the challenges of suburban schoolyards. Together, these cases capture the diversity of building forms and green spaces in Portuguese schools, enabling analysis of how context and site-specific characteristics influence outdoor usability and thermal comfort.

3. Research Methodology

This study’s methodological approach builds upon prior research on participatory design in schoolyards [11], the role of urban green spaces in microclimate regulation [4,8], and the influence of socio-economic context on school infrastructure. We implemented a multi-faceted strategy with the following components:

• Community Survey: An online questionnaire in Portuguese was designed to gather perceptions from students, teachers, and staff at both schools regarding their campus environments (Figure 2 and Figure 3). Drawing on the research team’s previous experience with online questionnaires assessing students’ use and perceptions of school spaces, the instrument had already been tested and validated for reliability. Furthermore, a preliminary sample survey was conducted to evaluate the adequacy of the vocabulary, thereby minimizing potential bias [11]. With support from the school administrations, the survey was distributed electronically and remained open from 4 to 18 June 2024. A total of 214 responses were collected (93 from ESJF and 121 from ESDD). This corresponds to 8.2% of the ESJF population and 19.7% of the ESDD population, with responses evenly distributed across age and gender, thereby supporting the validity of the sample. The questionnaire, administered via Google Forms, included both general and site-specific questions, which were adapted to each school’s layout and conditions (Figure 3). Respondents were asked about the frequency of use of various outdoor spaces, the thermal comfort of those areas during different seasons, satisfaction with the amount and quality of vegetation, and suggestions for improving comfort in both classrooms and recreational areas. Both quantitative (e.g., rating scales on thermal sensation) and qualitative (open comments) data were obtained. The survey also probed perceptions of how the school’s outdoor environment affects academic performance and well-being.
• Thermo-hygrometric Measurements: We conducted on-site measurements of air temperature and relative humidity at each school during late spring/early summer under stable anticyclonic weather conditions. Measurements were taken on clear days at three key times: morning (around 8:00–9:30, before classes), midday (1:15–2:45 PM, peak heating period during lunch/recess), and late afternoon (6:00–7:30 PM, after classes, during the cooling phase). At ESJF, data were collected on 9 May 2024 (daily range ~15 °C to 28 °C; 40–65% RH). At ESDD, data were collected on 29 May 2024 (range ~13 °C to 30 °C; 52–89% RH). A Lutron AM-4247SD data logger was used for air temperature (accuracy ± 0.8 °C) and humidity (precision ± 0.1% RH) readings. For outdoor areas, we established a grid of measurement points covering all main schoolyard zones. Repeated readings at these points during the three intervals were later interpolated using ArcGIS Pro 3.5. to produce continuous temperature and humidity maps of each campus. For indoor environments, representative spaces were selected: several classrooms (with single-point measurements ~1.5 m above floor level, assuming within-room homogeneity), corridors on multiple floors, and gymnasiums (with multiple points to capture gradients).
• Spatial and 3D Analysis: To assess the microclimatic impact of the proposed interventions, spatial and three-dimensional (3D) analyses were conducted, beginning with the spatialization of outdoor thermal conditions. Temperature data collected on-site were interpolated using Empirical Bayesian Kriging (EBK), a geostatistical technique that accounts for spatial autocorrelation and prediction uncertainty. This method enabled the generation of continuous surface maps, revealing temperature distribution patterns across the schoolyards and identifying areas of thermal stress.

Subsequently, 3D modeling was employed to analyze the spatial behavior of shadows in key outdoor areas. Simplified models of each school site were developed in SketchUp using architectural plans and high-resolution satellite imagery, incorporating existing vegetation and built structures. These models were imported into Twinmotion to simulate solar exposure and shadow projection at different times of day and year. The analysis focused on estimating the extent, timing, and location of shaded areas in relation to student circulation and activity zones. This helped to verify the potential effectiveness of each design intervention in increasing shade coverage where it is most needed.

Nevertheless, it is important to acknowledge that both the geospatial and 3D modeling approaches rely on methodological assumptions that may influence the robustness of the conclusions. For instance, EBK interpolations are dependent on the spatial density and representativeness of the sampling points, while simplified 3D models inevitably omit finer-scale elements of vegetation morphology and material properties that affect microclimatic behavior. Moreover, shadow simulations presuppose standardized atmospheric conditions and do not account for potential variability in cloud cover or seasonal vegetation changes. These limitations introduce a degree of uncertainty into the results and should be considered when interpreting the effectiveness of the proposed interventions.

By combining quantitative microclimatic data with qualitative user perceptions, our methodology provides a holistic view of thermal comfort at the two schools. The data triangulation enables us to pinpoint not only where thermal extremes occur on campus, but also when and how they affect the school community, thereby guiding targeted, co-designed mitigation strategies.

4. Results and Data Analysis

4.1. Community Use and Perceptions of Green Spaces

The online survey provided valuable insights into how the school communities use and perceive their green spaces. Most respondents at both ESJF and ESDD agreed that greenery on campus is important for comfort and well-being, with 79.6% at ESJF and 72.7% at ESDD rating it as “important” or “very important.” Nevertheless, the frequency and enjoyment of green space use differed significantly between the two schools, reflecting disparities in spatial quality and accessibility.

At ESJF (Figure 4), respondents expressed appreciation for the idea of a greener schoolyard but were critical of the current conditions. Many pointed out that the existing green areas were scarce, of poor quality, or largely inaccessible. As a result, students tended to avoid the small garden areas during recess, especially in hot weather, and instead congregated on the open asphalt court despite its discomfort. Survey questions about specific outdoor locations identified four main problem zones (A1–A4 on the ESJF campus map) that were perceived as thermally uncomfortable, being too hot in summer and too cold in winter. Area A1, which includes the main eastern sports yard and its adjoining sub-area A1a, is a large asphalt surface with minimal shade, where the dark pavement causes intense heat accumulation. Area A2, a smaller adjacent yard, was also described as unbearable in summer due to its lack of vegetation. Area A3, a lower-level space, offered little shade and was perceived as sun-exposed and uninviting. Finally, Area A4, a compact corner near older infrastructure, combined inadequate shading with deteriorated equipment and therefore received the lowest comfort ratings. A small central courtyard (A5) exists but is mostly inaccessible to students and was therefore excluded from the survey. Similarly, Area A6, a restricted green patch, was not part of the formal questionnaire (Figure 2—Question 20), although it was frequently mentioned in open responses. Many respondents regarded these locked or off-limit green spaces as missed opportunities to improve both comfort and aesthetics.

At ESDD (Figure 5), the survey revealed a rather different situation. Respondents were less concerned about extreme outdoor heat, thanks in part to the greater tree cover, but raised issues regarding winter conditions and maintenance. The main complaint concerned cold classrooms during the winter months, pointing to structural deficiencies in insulation and heating. Regarding outdoor areas, the central plaza (Area A1) was the most frequently used space during breaks. It benefited from partial shading and received relatively positive thermal ratings, although students noted a lack of seating and amenities. The unpaved dirt field (Area A2), located at the far end of the campus, was rarely used and criticized for being dusty in summer, muddy in winter, and generally neglected in terms of maintenance. The semi-paved yard between buildings (Area A3) presented moderate microclimatic conditions but was judged to lack recreational equipment. The zone near the sports courts (Area A4) was perceived as overly exposed and windy, with inadequate shading and deteriorated sports facilities. By contrast, Area A5, a greener space with trees and benches, was considered one of the most comfortable areas in terms of temperature, though respondents still suggested improvements in shaded seating and tree maintenance.

Across both schools, several common themes emerged from the surveys. Since no significant differences were observed across demographic groups, namely age, gender, or grade, the results can be considered generalizable. Students and teachers desired more shade in outdoor spaces, whether from trees or built structures, to allow comfortable use of yards in summer. Many also emphasized the poor state of outdoor furniture and play/sports equipment, which, if improved, could encourage people to spend more time outside even in marginal conditions. Maintenance issues were highlighted: for instance, unwatered plants, litter, or broken pavement made some areas less inviting. A noteworthy finding was the clear gap between appreciation of green spaces in theory and actual usage in practice—even when people recognize the benefits of greenery, they would not use a space unless it is comfortable and well-designed. This underscores the need for participatory co-design in any intervention, ensuring that upgrades to school grounds (e.g., planting trees, adding shade canopies, or seating) align with the needs and preferences of the users.

4.2. Microclimatic Measurements: Thermal Profiles of Indoor and Outdoor Spaces

4.2.1. Indoor Environments

At ESJF, which features a multi-story main building and an older design, morning measurements (8:00–9:30 AM) already showed notable thermal stratification. East-facing classrooms—which receive direct sunlight shortly after sunrise—were the warmest, reaching around 23–24 °C, whereas classrooms facing north or south started the day a few degrees cooler (around 18–19 °C) but slightly more humid (over 60% RH) due to reduced early sun and possibly overnight ventilation. By midday (1:30–2:45 PM), indoor temperatures in the sun-exposed east wing climbed further (some east-facing rooms peaked at ~25 °C), and even upper-floor classrooms in the main block reached ~24 °C, despite the high thermal mass of the 1930s building. Relative humidity indoors dropped by roughly 5–10% from morning values by this time (down to ~50–55% RH in many rooms), consistent with heating of the air. By late afternoon/early evening (6:00–7:30 PM), as outdoor temperatures began to fall, most classrooms showed slight cooling but remained warm (persistently above 22 °C on upper floors). Interestingly, the gymnasium at ESJF, a high-volume space with less insulation, did not heat up as much as classrooms during the day but also retained heat longer into the evening. Indoor humidity levels by 6 PM tended to rebound toward morning levels as temperatures fell, except in spaces like the gym that had significant occupancy (which can raise humidity through human presence). In summary, ESJF’s older construction and east–west orientation led to some areas (east-facing and top-floor rooms) being consistently warmer and drier, pointing to a need for shading (e.g., awnings or tree cover) and ventilation improvements for those hotspots.

ESDD’s pavilion-style layout yielded a somewhat different indoor profile. In the morning, temperatures in most classrooms were relatively uniform (generally 18–20 °C), but humidity was higher on ground floors (~65% RH) than upper floors (~55–60% RH). This likely reflects cooler, moist air near the ground and possibly better shading from trees for the lower rooms, as several blocks have adjacent trees that shield early sun. By early afternoon, ESDD saw a more pronounced spike in certain areas: for instance, the sports pavilion (gym) interior temperature jumped by about 9 °C from morning, reaching the high 20 s (°C)—this was partly due to a combination of weather and usage (a scheduled PE class during measurement). Similarly, Building F’s west-facing classrooms, which receive full sun in the afternoon, saw sharp temperature rises (often 4–5 °C higher than their east-facing counterparts in the same building). In Building A, which has one side shaded by trees and another exposed, we measured a ~2 °C difference between the east-facing (tree-shaded) classrooms and west-facing rooms during peak heat. By 6 PM, most indoor spaces at ESDD had cooled down to near-morning temperatures, thanks to the evening air and cross-ventilation (the open corridors may facilitate airflow). An exception was the gymnasium, where residual heat and possibly continued activity kept humidity somewhat elevated (in contrast to classrooms where humidity dropped as students left). Overall, ESDD’s more modern, spread-out design benefitted many classrooms by giving them cross-ventilation and some tree shade, but it also meant that those lacking shade (especially west-facing) experienced significant midday thermal stress.

4.2.2. Outdoor Environments

The microclimate maps for the schoolyards (Figure 6 and Figure 7) vividly illustrate how green cover moderates the microclimate, especially during peak heat periods. In the morning (around 8:15–9:30), both campuses showed relatively small spatial temperature differences (<2 °C) as the night’s coolness lingered. However, even at this time, areas above heat-storing surfaces were starting to warm faster and had lower humidity than grassy or treed areas. Notably at ESJF (Figure 6), the open asphalt sports field on the east side had among the lowest relative humidity readings in the morning (~30%, several points lower than the forecast ambient RH), indicating how a bare sunlit surface quickly dries the air above it. Meanwhile, the vegetated patches and the courtyard with trees maintained higher RH (~40%+) and slightly cooler temperatures than their surroundings, essentially acting as early-morning moisture refuges.

By early afternoon (around 13:15–14:45), as expected, the differences became far more pronounced. At ESJF (Figure 6), sun-exposed hardscape areas (e.g., the basketball court, bare ground near buildings) heated up to over 34 °C, whereas the coolest recorded spots-beneath the cluster of linden trees (Tilia spp.) and in the shaded corner of the main courtyard—were around 29–30 °C. Thus, trees were providing a cooling up to ~4 °C within roughly a 15–20 m radius of their canopy. Correspondingly, mid-afternoon relative humidity plummeted to ~20–25% in the hottest, unshaded zones (notably the eastern asphalt and near a sunlit wall by the student cafeteria), whereas the tree-covered area retained RH closer to 30–35%. Interestingly, the highest RH values at that time (~40%) were measured in a grassy zone that was partly shaded and also exposed to a breeze, suggesting cooling due to evapotranspiration from soil and turf. By late afternoon (6:00 PM), as the sun angle lowered, some previously shaded areas became sun-exposed and vice versa, slightly shifting the pattern. ESJF’s overall yard temperature began to decline (most areas fell to 25–28 °C), but the earlier thermal inertia meant some spots stayed warm. The asphalt court, for instance, remained one of the warmer surfaces even without direct sun, due to stored heat. Humidity levels by early evening rebounded in many areas—grass-covered sections climbed back above 40% RH as they cooled, whereas the driest air (still ~21–25% RH) lingered over the artificial surfaces that were slow to cool. ESJF’s outdoor thermal maps underline that vegetation and shade not only reduced peak temperatures but also helped moderate humidity, whereas expansive paved areas experienced stark hot-and-dry conditions at midday.

At ESDD (Figure 7), the larger amount of greenery led to generally smaller thermal gradients across the site. On the cool spring morning measured, almost the entire schoolyard was a uniform ~13–15 °C, with relative humidity around 65–70% everywhere. The tall pines and cypresses, along with building shadows, kept the early day microclimate fairly even (and as some staff noted, even cold in certain classrooms). By early afternoon, however, differences emerged: the open eastern sports field (with no tree cover) became the hottest area, reaching ~32–33 °C on its bare soil surface, and correspondingly its RH dropped to near 30% (from ~50% mid-morning). In contrast, the western tree grove (pine trees near Building B/C) and the greenspace around the gym stayed much cooler—around 27–28 °C—providing a cooling of about 5 °C relative to the exposed field. These vegetated zones maintained RH in the mid-40 s%, markedly higher than the exposed areas. Notably, unlike ESJF, ESDD’s tall evergreen canopies did not boost humidity as much; the dense pine stands provided shade that kept temperatures low, but the measured RH under them was only slightly higher than outside (trees moderate temperature more than they directly add moisture). Another observation at ESDD was the effect of wind: during our measurements, a gentle northerly breeze funneled through the open field, which likely helped cool that area faster by late afternoon. Indeed, by 6:00 PM the eastern field had shed much of its heat and was no longer the hottest spot; instead, the built areas (Building F/C) and the main entrance plaza, which absorbed heat all day, were relatively warmer in the late day. Relative humidity across ESDD in the evening was fairly uniform (around 60%), indicating the entire site re-equilibrated as temperatures leveled off. Overall, ESDD’s outdoor data demonstrate that even in a greener campus, timing and distribution of sun exposure matter: at midday there was a sharp contrast between the comfort of shaded lawns (pleasantly cooler) and unshaded grounds (uncomfortably hot). By planting more trees or creating shade in those exposed spots (like the sports field), the school could mitigate the short but intense thermal extremes they currently face at the peak of the day.

5. Discussion

The results of this study highlight the significant impact that greening and design modifications can have on improving thermal comfort in school settings. Studying two schools with distinct architectural typologies provided a rich perspective on the challenges and opportunities for climate adaptation in educational environments. Both ESJF and ESDD currently exhibit features of an “arid” school microclimate, largely due to insufficient vegetation cover and heat-retaining construction. However, the nuances between the two sites offer valuable lessons on how design and maintenance influence thermal outcomes, which we discuss below, along with proposed solutions informed by the data and literature (Figure 8).

At ESJF, the combination of an older, compact building layout and large asphalt surfaces has created pronounced thermal stress. The lack of natural shade over the main yard means that during sunny days this area becomes a heat sink, corroborating the students’ feedback of avoiding it during extreme heat. The east-facing classroom wing exemplifies how building orientation without adequate shading leads to morning overheating—by midday those rooms were uncomfortably warm, a pattern also observed in similar urban school buildings without external shading [3]. Meanwhile, the north-facing classrooms stayed cooler but felt stuffy and humid, suggesting a ventilation issue. Although ESJF has some trees, they are too few and mostly peripheral; their cooling benefit did not extend to upper floors or deeper courtyard zones. These observations align with studies showing that a sparse or isolated tree canopy in dense urban settings provides only limited microclimate regulation [25]. In essence, ESJF’s campus suffers from design legacies (extensive paving, courtyard enclosure) that concentrate heat, and its scant greenery is insufficient to counteract this, especially for upper-story environments.

ESDD, with its pavilion-style spread and more plentiful green space, fared better overall in thermal comfort, yet it too had notable issues. The data and community feedback both point to maintenance and distribution problems rather than a sheer lack of vegetation. For example, ground-floor classrooms in ESDD stayed reasonably cool thanks to tree shade, but when those trees are tall and limbed-up (like the cypresses along the edge), they provide shade without much evapotranspiration at the human level, sometimes creating “dry shade” conditions. Indeed, we noted that areas under row-of-cypress plantings were not as cool as under broad-canopied pines, indicating canopy density is key. This echoes findings by [26] hat denser foliage and appropriate species selection significantly enhance shading efficiency in urban greenspaces. ESDD’s survey also revealed that many students avoided certain outdoor areas not only due to thermal discomfort but because those areas were unattractive or poorly equipped. For instance, the seldom-used dirt field (A2) contributes little to the microclimate (it is an expanse of bare ground that becomes very hot), and simultaneously it offers no recreational draw—a worst-of-both-worlds situation. By contrast, the more vegetated corners of ESDD were valued for comfort but could not fully compensate for a lack of functional amenities. In summary, while ESDD demonstrates the potential of distributed greenery (it clearly moderated the campus climate, as our measurements show), it also illustrates that green infrastructure must be coupled with usability and care to make a meaningful difference in daily school life.

Given these insights, what interventions can enhance thermal comfort in such school environments? Our study strongly supports a suite of nature-based and design solutions, grounded in the microclimate data and community suggestions:

• Increase Tree Canopy and Strategic Planting: Both schools would benefit from more trees, particularly deciduous species with broad canopies planted in high-exposure areas (south- and west-facing sides of yards and buildings). At ESJF, new tree plantings around the eastern sports court and within the central courtyard could greatly expand shaded zones and lower surface temperatures by several degrees through evapotranspiration (“cool shade” effect). Deciduous trees are ideal here as they cool in summer and allow sun in winter [8,27,28]. At ESDD, creating small groves or “micro-woods” in currently open areas like the dirt field (A2) and near Building F would reduce the expansive heat patches. Species should be chosen for drought-tolerance and canopy density; for example, adding native or non-potential invasive shade trees like plane trees or oaks could complement the existing pines and cypresses to provide lower-level shade where needed [26].
• Greening of Bare Surfaces: Converting some of the asphalt or dirt surfaces into green or biophysical surfaces will directly mitigate heat. For ESJF, this could include replacing portions of the asphalt yard with permeable play turf or a garden area, which would cool the surface and add humidity. For ESDD’s dirt field, planting grass or native meadow species would prevent it from becoming a radiating “heat pad” and also improve its utility for recreation. Even small interventions like planting vines on fences or creating shrub borders can have a cooling impact and improve aesthetics.
• Shade Structures and Green Roofs/Walls: Where planting large trees is impractical (due to space or building constraints), built shade canopies or green structures are recommended. For instance, ESJF could install pergolas with climbing plants over parts of the courtyard or along the east facade to intercept morning sun in classrooms [29,30]. ESDD might consider tensile shade sails over the schoolyard equipment or seating areas in A1 and A4. Additionally, green roofs on flat sections of buildings (both at ESJF and ESDD) would reduce indoor heat gain and provide cooling due to evapotranspiration for the immediate surroundings. Green walls (vertical gardens) could be implemented on sun-exposed facades to insulate classrooms and cool the adjacent air [31,32]. These solutions have proven effective in other school settings for lowering surface temperatures and managing stormwater, bringing co-benefits of improved insulation and biodiversity habitat.
• High-Albedo and Porous Materials: Another complementary strategy is to use cooler paving materials in necessary hardscape areas. Re-surfacing yards with high-albedo (light-colored) [33] coatings or permeable pavers can significantly reduce heat absorption [25]. For example, the basketball court at ESJF, if kept asphalt, could be painted with a reflective coating to lower its surface temperature. Likewise, pathways at ESDD could use porous pavers that allow water infiltration and cooling [34]. While these are not nature-based per se, they work synergistically with vegetation (by retaining soil moisture and reflecting light into tree canopies, enhancing growth).

It is also important to situate these school-level changes within the broader urban context. In the case of ESJF, the school lies in a densely built central area already identified as an urban heat island hotspot [4]. Thus, the school’s greening could connect with citywide green infrastructure corridors (Figure 9).

By aligning the school’s planting strategy with these nearby elements—for example, using similar species or creating a vegetated walking route between the school and these parks—there is an opportunity to enhance ecological continuity and amplify cooling effects beyond the campus. Such connectivity would contribute to urban resilience by extending shade corridors for students walking to school and creating small “stepping stone” habitats for birds and pollinators, thereby enriching the urban fabric [25].

Finally, we highlight the role of environmental education and stewardship as a cornerstone of sustainable improvement. Technical fixes alone will not guarantee long-term success unless the school community values and maintains the green spaces. Both schools could implement programs where students actively participate in planting and caring for vegetation—for instance, forming “green brigades” to water young trees, or integrating garden-based learning into the curriculum [18]. These initiatives cultivate a sense of ownership and responsibility. When students help create a new shade garden or mural on a rainwater tank, they are more likely to use and protect those amenities. Over time, this can shift the culture: instead of seeing the outdoors as an uncomfortable or neglected space to avoid, the schoolyard becomes an extension of the classroom—a living lab where students learn about sustainability by doing. In our surveys, many students expressed willingness to be involved in such projects if given the chance. Thus, implementing the physical interventions hand-in-hand with educational components will reinforce their effectiveness and ensure that the green spaces remain functional, appreciated, and resilient to future challenges.

6. Conclusions and Lessons Learnt

Green spaces in schools are increasingly recognized not just for their aesthetic value but as essential elements for student and teacher well-being and for building climate resilience. This study, focusing on two urban schools in Coimbra, underscores several key lessons about designing and retrofitting educational environments for thermal comfort:

• Vegetation is Vital but Must Be Optimized: Simply having green areas is not enough—it is the quality, quantity, and placement of vegetation that determine its cooling effectiveness. At ESJF, a clear gap was observed between the presence of some trees and the actual thermal relief they provided; the few trees were either too peripheral or too small to significantly influence most spaces. At ESDD, a larger green footprint did translate to better comfort in general, but even there, uneven tree distribution (with some areas over-planted and others bare) led to hot spots. Schools should prioritize planting deciduous shade trees in the most sun-exposed locations and around key activity areas. Trees with broad canopies and, where possible, drought-resistant traits are ideal. In exposed pavements or courtyards, adding even small clusters of trees or shrubs can yield disproportionate benefits by breaking up large radiant surfaces.
• Maintenance and Access Matter: A well-designed green space that is inaccessible or poorly maintained will not serve its purpose. Both case studies revealed maintenance issues—dried-out lawns, unpruned trees, or neglected planters—which diminished the potential benefits of those green features and sometimes even caused discomfort (e.g., uncleared leaf litter can be slippery, overgrown areas might harbor pests). Ensuring regular upkeep (watering, pruning, cleaning) is as important as the initial installation of green infrastructure. Moreover, opening up previously off-limits vegetated areas (like ESJF’s courtyards) for supervised student use can instantly improve the user experience. Involving students in maintenance (through eco-clubs or class projects) can alleviate some of the resource burden while providing educational value.
• Synergy of Design Interventions: The greatest improvements in thermal comfort will come from a combination of approaches. For example, at both schools we identified that adding trees would help, but trees take time to grow. In the interim, installing shade sails or canopies can provide immediate relief. Likewise, a tree planted next to a reflective wall will have more impact if the wall is also painted a light color to reduce heat absorption. Our findings advocate for an integrated design: green (vegetation) plus gray (built shade and cool materials) together. Such synergy was evident at ESDD, where covered walkways plus adjacent trees made outdoor circulation reasonably comfortable even on hot days. Future school designs should consider pergolas with climbing vines, courtyards with a mix of trees and tensile structures, and play areas that alternate softscape with hardscape to balance functionality with comfort.
• Community Engagement and Education: Perhaps the most important lesson is that successful sustainable design in schools involves the users at every stage. The differences we saw between the two schools’ usage of spaces were not only due to physical factors but also due to how students perceived and valued those spaces. A participatory process—from surveying needs, to co-design workshops, to student-led planting days—can generate a sense of ownership that ensures long-term success. Our project showed that students are keenly aware of their environment’s shortcomings and often have creative ideas to offer. Empowering them to be part of the solution (for instance, letting them design a mural on a new rainwater cistern or choose species for a small garden) can lead to more widely accepted and respected outcomes. Environmental education programs that tie into these real-world projects amplify the impact, turning the school into a microcosm of sustainable practice. As a result, not only is the immediate goal of thermal comfort met, but the school also fulfills its broader educational mission by equipping young people with knowledge and experience in climate adaptation and stewardship. Building on this conclusion, further developments could incorporate feedback from a broader school community, including parents, alumni, local residents, and a wider range of school users. Ultimately, inputs from a more diverse group of stakeholders would, on the one hand, provide a broader set of recommendations and demonstrate the robustness of the previous findings, and, on the other hand, foster community engagement and promote participatory co-creation on a larger scale.
• Scalability and Urban Integration: Improvements made at the school level can have ripple effects in the urban ecosystem. The initiatives suggested—planting trees, creating green roofs, etc.—contribute cumulatively to urban cooling and air quality if adopted widely. There is an opportunity for schools to serve as community hubs or demonstrators of climate resilience. For example, a network of green schoolyards across a city can form a patchwork of cooler zones that mitigate the urban heat island. In Coimbra, connecting ESJF’s greening efforts with nearby parks and tree-lined streets (as illustrated conceptually in this study) would magnify benefits for the neighborhood at large. City planners and educational authorities should view school refurbishment projects as part of the urban green infrastructure strategy. Funding mechanisms and policies could encourage schools to adopt nature-based solutions by highlighting not only the pedagogical and health benefits, but also the municipal gains in resilience.
• Sustainability Strategies: The proposed greening interventions in schoolyards not only address local thermal discomfort but also align directly with several Sustainable Development Goals (SDGs), namely SDG 3 (Good Health and Well-being), SDG 4 (Quality Education), SDG 11 (Sustainable Cities and Communities), and SDG 13 (Climate Action). By enhancing microclimatic resilience in educational facilities, these measures contribute to the European Green Deal’s objectives of promoting climate-neutral, resource-efficient, and health-conscious urban environments, while simultaneously supporting national and municipal climate adaptation strategies. Moreover, the cumulative effect of implementing green infrastructure across multiple schools extends beyond campus boundaries, mitigating urban heat island dynamics, improving air quality, and strengthening ecological connectivity in densely built areas. In this way, schools can serve as pivotal nodes within broader urban sustainability networks, functioning not only as spaces of learning but also as demonstrators of climate adaptation, thereby reinforcing the integration of local interventions with global policy frameworks.