Researchers from the University of Hail, Imam Mohammad Ibn Saud Islamic University, Dar Al-Hekma University, and Aswan University tackled a problem that has long frustrated urban designers and landscape architects in hot-arid regions: while urban vegetation is widely recognized as a passive cooling strategy, its actual performance depends on a complex interplay between the tree’s physical characteristics and the surrounding built environment. A tree that provides exceptional shade in one courtyard orientation may perform far less effectively in another. A species that delivers dramatic peak-hour cooling may not maintain that benefit throughout the school day. Conventional assessments that rely on a single thermal variable, such as air temperature reduction, simply cannot capture this multidimensional nature of vegetation performance.

To address this gap, the research team developed what they call a Multi-Criteria Thermal Performance Framework, or MCTPF. The framework integrates high-resolution microclimatic simulations using ENVI-met software with physiological equivalent temperature, or PET, calculations to evaluate vegetation performance across three complementary dimensions. The first dimension, quantified through the Tree Cooling Efficiency Index, measures the magnitude of integrated thermal improvement relative to a non-vegetated baseline. The second, captured by the Thermal Resilience Index, assesses whether a vegetation scenario reduces temporal variability in thermal conditions throughout the assessment period. The third, expressed through the Orientation Sensitivity Index, quantifies how much cooling effectiveness changes when the same vegetation configuration is evaluated under contrasting courtyard orientations. These three indices are subsequently integrated through a Composite Thermal Performance Index after normalization to a common performance scale.

The study focused on two semi-enclosed courtyards at the Egyptian Japanese School, each with an identical footprint of 200 square meters but with critically different orientations. The primary courtyard opens toward the east, while the secondary faces west. This asymmetrical configuration creates fundamentally different patterns of solar radiation absorption and wind interaction throughout the school day, establishing diverse thermal microenvironments within the same building complex. The researchers established a non-vegetated baseline scenario for each courtyard and then modeled three alternative vegetation scenarios by introducing individual tree species: Cassia leptophylla, commonly known as the gold medallion tree; Ficus nitida, or the Indian laurel; and Cassia nodosa, the pink shower tree. Each species was represented in the ENVI-met model using its actual morphological characteristics, including tree height, canopy diameter, leaf area index, and canopy porosity, rather than imposing an artificial standardized geometry.

The simulation results revealed substantial differences among the modeled vegetation configurations and between the two courtyard orientations. Ficus nitida consistently produced the greatest cooling response across all three thermal variables. In the east-facing courtyard, this species reduced air temperature by approximately 5.02 percent, mean radiant temperature by 37.88 percent, and PET by 25.39 percent relative to the baseline. In the west-facing courtyard, the corresponding improvements were 4.57 percent, 25.48 percent, and 15.35 percent respectively. The substantially larger reductions in mean radiant temperature compared to air temperature demonstrate that the principal cooling contribution of these tree scenarios was associated with modification of the radiative environment through shading and interception of solar radiation rather than with large reductions in ambient air temperature.

However, the story became considerably more nuanced when the researchers evaluated performance across all three dimensions simultaneously. While Ficus nitida achieved the highest Tree Cooling Efficiency Index values in both courtyards, with scores of 0.251 in the east-facing courtyard and 0.162 in the west-facing courtyard, it also exhibited the greatest sensitivity to courtyard orientation, with an Orientation Sensitivity Index of 0.428. In contrast, Cassia leptophylla demonstrated the greatest orientation robustness, with the lowest OSI value of 0.272, despite producing the lowest cooling efficiency among the three species. Cassia nodosa occupied an intermediate position, combining moderate cooling performance with the highest Thermal Resilience Index in the east-facing courtyard, indicating superior temporal stabilization of thermal conditions under that orientation.

The Composite Thermal Performance Index revealed clear trade-offs among cooling magnitude, temporal stability, and orientation robustness. Ficus nitida in the east-facing courtyard achieved the highest overall CTPI value of 74.75, reflecting its dominant cooling efficiency and near-maximum temporal resilience. However, its high orientation sensitivity resulted in the lowest orientation-robustness score, which limited its composite performance under the less favorable west-facing courtyard condition, where its CTPI dropped to just 21.06. Conversely, Cassia leptophylla, despite its lower cooling efficiency, achieved the highest CTPI in the west-facing courtyard at 25.00, benefiting substantially from its superior orientation robustness. The ranking of vegetation configurations changed between the two courtyard orientations, confirming that the same tree species can exhibit fundamentally different integrated thermal performance depending on its spatial context.

The researchers conducted a sensitivity analysis to examine whether alternative weighting structures would alter the comparative ranking. Under the baseline structure, which assigned the greatest weight to cooling efficiency, Ficus nitida in the east-facing courtyard remained the preferred alternative. However, when orientation robustness received substantial importance, Cassia leptophylla became the preferred configuration. This finding demonstrates that the framework does not impose a universally optimal vegetation choice but rather provides a transparent mechanism for adapting tree-selection decisions to different thermal-design priorities while preserving the spatial influence of courtyard orientation.

Model validation showed strong agreement between simulated and measured air temperature patterns, with a coefficient of determination of 0.996 and a mean absolute error of 1.505 degrees Celsius. Relative humidity demonstrated even stronger agreement, with a coefficient of determination of 0.9998. However, the researchers acknowledge that the validation was based on baseline measurements at a single location over one 24-hour period and did not directly validate vegetation-induced thermal responses. Mean radiant temperature, wind conditions, PET, and the magnitude of vegetation cooling were not independently validated against field measurements, meaning the findings should be interpreted primarily as comparative simulation-based evidence rather than fully validated predictions of absolute thermal conditions.

The implications of this research extend well beyond a single school in Aswan. As cities across the Middle East, North Africa, and other hot-arid regions grapple with intensifying urban heat, the framework offers a transparent and reproducible pathway from microclimatic simulation to climate-responsive design selection. Rather than asking simply which tree provides the greatest temperature reduction, designers can now evaluate vegetation strategies according to clearly defined priorities: whether maximum cooling efficiency matters most, whether temporal stability throughout the occupancy period is the primary concern, or whether robustness across different spatial orientations should dominate the decision. The framework makes these trade-offs explicit, allowing vegetation selection to respond to specific courtyard conditions and design objectives rather than relying on single-variable comparisons that may mask critical performance differences. The researchers emphasize that future studies should validate vegetation-induced thermal effects through field measurements across broader environmental contexts, examine multiple seasons and climatic regions, and incorporate age-specific physiological parameters to better represent the children and adolescents who constitute the primary users of educational courtyards.

Subject of Research: Tree selection, courtyard form, and outdoor microclimatic comfort in hot-arid educational spaces: a multi-criteria decision framework

Article Title: Tree selection, courtyard form, and outdoor microclimatic comfort in hot-arid educational spaces: a multi-criteria decision framework

Article References: Aldersoni, A., Abdallah, A. S. H., Abdelhafez, M. H. H., Elkhayat, K., Gomaa, M. M., & Ragab, A. (2026). Tree selection, courtyard form, and outdoor microclimatic comfort in hot-arid educational spaces: a multi-criteria decision framework. Frontiers in Built Environment, 12, Article 1956270. https://doi.org/10.3389/fbuil.2026.1956270

Image Credits: AI Generated

DOI: 10.3389/fbuil.2026.1956270

Keywords: ENVI-met, PET, TCEI, TRI, OSI, CTPI, courtyard orientation, hot-arid climate, school courtyards, tree selection, thermal comfort, urban vegetation

The research, led by Floralba Pirracchio Massimino with colleagues Rui Alexandre Castanho, Inmaculada Gómez, and Javier Velázquez, tested its Sustainable Greening Upgrades protocol in Catania, a Sicilian city of roughly 296,500 inhabitants whose historic core was largely rebuilt after the 1693 earthquake in Baroque style and now forms part of the UNESCO-listed Late Baroque Towns of the Val di Noto. The team focused on a 2.22 square kilometer sample area within the historic center, a fabric they characterize as compact mid-rise: continuous building blocks, medium heights, extensive impervious surfaces, and very limited vegetation. The area houses about 18,432 residents and has a built-coverage ratio of 0.68, meaning more than two thirds of the ground is occupied by buildings, with most of the rest sealed in one way or another.

The urgency behind the work is stark. The June 2025 heatwaves tripled heat-related deaths in Europe, and Mediterranean cities are warming faster than many other European regions. Previous studies of Catania had already shown that land cover is the main driver of surface temperature differences observed by satellite, with gaps of 15 to 17 degrees Celsius between green and built areas both day and night. In Thessaloniki, the historical center records mean land surface temperatures of about 29 degrees with peaks above 31 degrees due to canyon effects, and similar constraints have been documented in Florence. What has been missing, the authors argue, is a practical bridge between diagnosis and design: maps of urban heat are abundant, but concrete, georeferenced micro-sites ready for intervention are not.

The protocol’s methodological core is a five-stage decision chain built entirely from open or routinely available spatial data. First, the study area is delimited morphologically. Second, satellite imagery is preprocessed to produce diagnostic layers of land surface temperature and vegetation. Third, deficits in urban green space are mapped using a 200-meter service-area buffer around existing parks larger than 500 square meters. Fourth, candidate urban voids are delineated and prioritized. Fifth, the hottest and most transformable sites are evaluated in a microclimate simulation. The team retrieved land surface temperature from Landsat 8 thermal imagery acquired on 15 July 2025, applying radiometric conversion, brightness-temperature calculation, and NDVI-based emissivity correction, then disaggregated the 30-meter thermal data to 10 meters using Random Forest regression with Sentinel-2-derived predictors, achieving an internal model fit of R-squared 0.91 with a root-mean-square error of 1.8 degrees Celsius.

The definition of an urban void is deliberately operational rather than poetic: a mineral, sealed interstitial space between 15 and 100 square meters. Candidate sites had to satisfy six screening criteria, including a Normalized Difference Vegetation Index below 0.2, a surface temperature above 45 degrees Celsius, public or semi-public ownership, physical accessibility, and a distance of more than 100 meters from an existing green space. Crucially, the geometry of these voids was not derived from the coarse satellite raster but mapped independently by vector photointerpretation of high-resolution orthophotography, with the satellite layers serving only as diagnostic covariates assigned to each polygon. This separation avoids implying sub-pixel precision that the 10-meter data cannot deliver.

Applying these criteria across the surveyed extent of the Civita and San Cristoforo sectors, roughly 0.70 square kilometers, the team identified 127 urban voids covering 6,784 square meters, or 0.98 percent of the surveyed area. The units ranged from 19 to 94 square meters with a mean of 53.4 square meters. Thermal classification placed 23 voids in the hottest priority class above 50 degrees Celsius, 59 in the 47-to-50-degree band, and 45 in the 45-to-47-degree band. Notably, the two sectors differed in thermal severity rather than in the overall density of voids: 27.5 percent of San Cristoforo’s voids reached the highest thermal class against 11.8 percent in Civita, a statistically significant difference. Sensitivity tests on the size criterion showed the 23-site priority subset was robust, remaining unchanged under most alternative size ranges tested.

To separate thermal need from practical feasibility, the researchers introduced a transformability index that scores each site for usable size, operational accessibility, ownership regime, and utility interference, then multiplies by limiting factors for pavement removability and heritage restriction. The hybrid additive-multiplicative form reflects a key reality of protected historic fabrics: a single prohibitive condition, such as listed lava-basalt paving or direct appurtenance to a monument protected under Italian heritage law, can cancel feasibility entirely and would otherwise be averaged away. The 23 priority sites all scored at or above the 0.6 admissibility threshold, with archived scores ranging from 0.60 to 0.85 and a median of 0.70. The authors are careful to stress that these are expert-assigned scores and that heritage compatibility is a second-stage constraint, not a guarantee that every candidate site is immediately implementable.

The design scenario transformed the 23 priority voids into Micro Green Units through full depaving, sustainable drainage systems with a substrate albedo of 0.25, and one six-meter Celtis australis, the Mediterranean hackberry, per unit, with a leaf area density of 1.5 square meters per cubic meter. Simulations in ENVI-met V5.1.1 at 2-meter horizontal resolution compared the sealed baseline against the greened scenario over a 24-hour period on 15 July 2025, using hourly forcing data from the ARPA Sicily Catania Center station and an initial soil wetness of 30 percent. Outputs were averaged over the 14:00 to 16:00 UTC afternoon window at 1.5 meters above ground.

The modelled results are striking. Within the 23 greened units, mean land surface temperature fell by approximately 8.3 degrees Celsius, with a peak reduction of 12.1 degrees, and nearly 87 percent of internal model pixels showed reductions greater than 5 degrees. Air temperature at pedestrian height dropped by an average of 2.1 degrees, with a maximum of 3.8 degrees, while Physiological Equivalent Temperature, a comfort metric combining temperature, humidity, radiation, and wind, decreased by 4.6 degrees on average, shifting conditions from the very hot class above 41 degrees into the hot class of 35 to 41 degrees. A modelled cooling signal also extended roughly 20 meters into the surroundings, with a mean surface-temperature reduction of about 3.2 degrees, though the authors emphasize this is descriptive rather than a quantified cooling radius. These magnitudes sit comfortably within published ranges for pocket parks and tree-lined Mediterranean courtyards, lending contextual plausibility to the scenario.

The authors are unusually candid about the limits of their findings. The cooling figures are deterministic model responses under a single meteorological day, one soil-moisture condition, and an idealized full-depaving assumption with intermediate-stage vegetation; they are not field-validated predictions, and a paired pixel-wise statistical test was demoted to descriptive status because spatial autocorrelation undermines independence. Uncertainties from the one-day offset between satellite acquisitions, the downscaling procedure, and an unexplained uniform rescaling of the scenario polygons relative to the mapped inventory are all flagged rather than hidden. Yet the study’s strongest contribution is methodological: a workflow-reproducible chain that links open-data thermal screening to independently delineated, georeferenced micro-sites, separates thermal need from transformability, and connects the selected subset to an ex-ante design scenario. As a form of green acupuncture for compact historic fabrics, the approach reframes urban greening from an aggregate deficit problem into a hunt for specific, mappable, and potentially transformable hot spots, offering heat-stressed heritage cities a realistic path to turn their smallest forgotten spaces into climate assets.

Subject of Research: Micro-scale urban greening of sealed voids to mitigate the urban heat island in the historic center of Catania, Italy

Article Title: Turning urban voids into climate assets: Micro green units for cooling historic cities

Article References: Massimino, F. P., Castanho, R. A., Gómez, I., & Velázquez, J. (2026). Turning urban voids into climate assets: Micro green units for cooling historic cities. Environmental and Sustainability Indicators, 32, Article 101545. https://doi.org/10.1016/j.indic.2026.101545

Image Credits: AI Generated

DOI: 10.1016/j.indic.2026.101545

Keywords: urban heat island, urban voids, micro green units, Catania, land surface temperature, ENVI-met, nature-based solutions, historic cities, remote sensing, Landsat 8, Sentinel-2, green infrastructure

The framework’s workflow is deliberately sequential and reproducible. Open datasets drawn from diverse sources are first processed in a GIS environment to derive the district’s urban morphology and material properties—building heights, street widths, surface coverings, vegetation cover and albedo values. That digital twin is then translated into a three-dimensional CFD domain, where the microclimate is simulated hour by hour, capturing the interplay of solar radiation, shading, surface temperature, humidity and wind flow through urban canyons. The simulation results are finally returned to the GIS as hourly rasters at a remarkably fine resolution of one square meter, enabling spatial and statistical analysis of thermal conditions across every street and square in the district. The authors validated the approach against in-situ temperature measurements, giving the modelled results an empirical anchor that many purely simulation-based studies lack.

What truly distinguishes the study, however, is not the modelling machinery but the metric it introduces: cumulative thermal stress. Conventional assessments of outdoor heat typically rely on snapshot evaluations—a peak-hour temperature map, a midday comfort index, a single worst-case moment. Such snapshots can seriously mislead, because two neighborhoods with identical afternoon peaks may impose very different total heat burdens on their residents depending on how long severe conditions persist. The new framework instead computes the hourly count of Universal Thermal Climate Index (UTCI) values above 32 °C, a widely used threshold for strong heat stress, effectively quantifying the total number of hours per day that a given location spends in dangerously stressful conditions. This cumulative measure translates abstract microclimate physics into something municipal decision-makers can act upon directly: hours of exposure, mapped street by street.

The UTCI itself is worth understanding, because the study’s most surprising result hinges on it. Unlike simple air temperature, the Universal Thermal Climate Index integrates air temperature, mean radiant temperature, humidity and wind speed into a single equivalent temperature describing how the human body actually experiences the environment. A street can feel brutally hot even when the air temperature is moderate, if surrounding surfaces radiate intense heat onto pedestrians and the air is still. This distinction is precisely where the study’s headline finding emerges: the intervention that cools the air most effectively is not the one that makes people feel most comfortable.

The research team compared three scenarios for the Seville district: baseline conditions with no intervention; an intervention raising surface albedo through reflective materials; and a combined strategy pairing reflective materials with urban greening. The reflective-materials scenario delivered exactly what proponents of cool roofs and cool pavements promise—a peak air temperature reduction of roughly 1.25 °C. But the high-resolution spatiotemporal analysis revealed a hidden cost. By bouncing more shortwave solar radiation back into the street canyon, the reflective surfaces raised mean radiant temperature during daylight hours, increasing the radiant heat load on pedestrians. The result was a worsening of daytime outdoor comfort as measured by UTCI, even as the air itself grew cooler. For anyone walking, waiting at a bus stop or working outdoors, the reflective district could feel harsher than the one it replaced.

The combined strategy told a strikingly different story. When reflective materials were paired with urban greening—trees and vegetation providing shade and evaporative cooling—the district achieved localized UTCI reductions exceeding 7 °C, a transformative improvement in how outdoor spaces feel during peak heat. Compared with reflective materials alone, the combined approach improved daytime comfort across more than 86 percent of the district. Crucially, when the authors applied their cumulative thermal stress metric, the combination delivered reductions of two to four hours in daily severe heat exposure, meaning residents in the hottest pockets of the neighborhood gained back hours of tolerable outdoor conditions every day. Shade from vegetation appears to be the decisive ingredient, intercepting solar radiation before it can heat pedestrian-level radiant environments while adding cooling through transpiration.

For cities across the Mediterranean and beyond, the implications are immediate and practical. Reflective materials remain a legitimate and valuable tool—air temperature reductions of over a degree matter for energy demand, nighttime cooling and indoor comfort—but the study demonstrates that they cannot stand alone in pedestrian-oriented urban regeneration. Deployed without complementary vegetation, high-albedo surfaces risk shifting the heat burden from the atmospheric domain to the human body, improving the numbers in a climate model while degrading the lived experience on the pavement. The one-meter-resolution mapping makes these trade-offs visible at exactly the scale at which residents experience them, allowing planners to identify which streets benefit from reflectivity, which need shade, and which require both.

The predictive character of the framework is its second major contribution. Because the workflow relies on open datasets and validated simulation, it can be applied to a candidate district before any capital is committed, ranking scenarios by their effect on cumulative exposure rather than on aesthetic preference or material cost alone. For municipalities with limited adaptation budgets—and few cities have unlimited ones—this provides a defensible, evidence-based method for prioritizing interventions in the most vulnerable neighborhoods first. The authors explicitly frame the work within the United Nations Sustainable Development Goals: reducing heat exposure advances inclusive and resilient cities (SDG 11), urban climate action (SDG 13) and the reduction of inequalities (SDG 10) through the same measure, since severe outdoor heat falls disproportionately on elderly residents, outdoor workers, children and low-income communities least able to escape it.

Methodologically, the integration of GIS and ENVI-met-style microclimate modelling through hourly raster exchange represents a template that other research groups and city governments can adapt. The study’s validation against field measurements addresses a persistent criticism of microclimate simulation—that its outputs can drift from reality—and its use of a Typical Meteorological Year drawn from data supplied by the Spanish State Meteorological Agency (AEMET) grounds the scenarios in representative climatic conditions rather than cherry-picked extremes. The cumulative stress metric, computed simply as hours above a UTCI threshold, is deliberately easy to communicate, which may prove as important as its scientific rigor: a city councilor does not need a physics degree to understand that an intervention that removes three hours of daily severe heat stress from a plaza is worth funding.

As climate change pushes summer temperatures in Southern Europe toward repeatedly breaking records, the gap between interventions that look effective on paper and those that genuinely protect residents is becoming a matter of public health. This study closes part of that gap with a clear, quantified warning: cooling the air is not the same as cooling the person, and the strategies that succeed are those engineered around the full human thermal experience—radiant load, humidity, wind and, above all, duration of exposure. In Seville’s most heat-vulnerable district, the winning formula was neither purely technological nor purely green, but a carefully modelled combination of the two, delivering seven-degree comfort improvements and hours of reclaimed safety every single day. That is the kind of measurable, street-level outcome that climate-resilient regeneration will need to deliver, and, thanks to this framework, cities can now predict it before they build it.

Subject of Research: Predictive assessment of urban outdoor thermal comfort and cumulative heat exposure for climate-resilient district regeneration using GIS modelling and CFD microclimate simulation

Article Title: Predictive assessment of urban comfort and cumulative heat exposure for climate-resilient district regeneration

Article References: Sola-Caraballo, J., Fiorito, F., Rivera-Gomez, C., & Galan-Marin, C. (2026). Predictive assessment of urban comfort and cumulative heat exposure for climate-resilient district regeneration. Discover Sustainability. https://doi.org/10.1007/s43621-026-04692-7

Image Credits: AI Generated

DOI: 10.1007/s43621-026-04692-7

Keywords: urban heat mitigation, UTCI, cumulative thermal stress, GIS-based modelling, CFD microclimate simulation, ENVI-met, climate-resilient planning, urban greening, reflective materials, albedo, Seville, district regeneration