Agnese Salvati

Vegetation in urban green spaces plays a critical role in mitigating surface heat, yet the magnitude of this effect remains uncertain across scales and measurement methods. This study assesses the cooling performance during the summer of 94 green spaces in three Chilean cities—classified in three types according to their size—combining satellite-derived land surface temperature (LST) data with high-resolution in situ thermal imaging. We performed comparisons of the cooling effects of green spaces and their components (vegetation, impermeable and semi-permeable surfaces). Spearman’s correlation analysis, the Mann-Whitney U test and Kruskal-Wallis and Dunn post hoc were used to evaluate associations and differences. Results demonstrate that vegetation quantity and composition—particularly tree and shrub cover—are key determinants of cooling performance. In situ measurements reveal that green spaces are on average 9.3 °C cooler than their urban surroundings, substantially exceeding differences captured by LST. Additionally, shaded surfaces within green spaces exhibit temperature reductions of 12 °C to 17 °C compared to sun-exposed areas, underscoring the role of vegetation in mitigating surface heat extremes. These findings challenge the sole reliance on remote sensing for urban heat assessments and highlight the value of integrating ground-based observations. This study advances understanding of vegetation’s localized cooling potential in Latin American cities and provides actionable insights for urban climate resilience planning.

Microclimatic conditions and activities in outdoor areas are dynamic in time and space. Such variability needs to be considered when assessing outdoor thermal comfort (OTC) and heat stress. This work proposes a methodology to analyse the spatio-temporal profiles of thermal comfort along pedestrian pathways. The analysis is based on simulated Physiological Equivalent Temperature (PET) data using the SOLWEIG model for two adjacent neighbourhoods in Barcelona, characterised by different urban form and vegetation cover. The thermal sensation along six representative pathways is compared. The results show a large variability of thermal profiles due to variations in urban morphology, vegetation and solar elevation. The heat stress severity of each pathway and time of the day is characterised in terms of magnitude (mean PET along the path) and exposure (total time of exposure to heat stress according to PET levels). The results show that the critical time of the day for heat stress along a pathway can change depending on the chosen criteria. In many cases, the critical time for exposure does not correspond to the time of maximum solar radiation. The profiles also highlight a great variability of patterns in terms of intermittency of thermal conditions and continuous exposure duration to heat stress conditions. The proposed methodology can provide valuable insights into the heat stress severity along pedestrian pathways, supporting the strategic placement of shelters to mitigate heat-related health risks and enhance OTC in urban areas.

Shade provision by buildings and trees is very beneficial in reducing pedestrian heat stress in hot climate regions, such as the Mediterranean. However, shade is not constant in time and space, which makes difficult to understand its actual potential to reduce pedestrian heat stress depending on the geometry and orientation of each urban space and the time of the day.In this work we present a framework to generate district-scale heat stress frequency maps based on the spatiotemporal variability of mean radiant temperature at the street level. This allows understanding the beneficial effect of a district urban geometry and vegetation on the thermal conditions of its urban spaces, as well as to identify where and when more shade is needed to reduce pedestrian heat stress.The approach is applied to the Gràcia district of Barcelona. First, we carried out high-resolution simulations of the radiation fluxes across the urban area using the SOLWEIG model. Then we correlated the Mean Radiant Temperature (Tmrt) to the PET values in the same points, to identify threshold values corresponding to different heat stress levels. Finally, we cross compared the spatial (maps) and frequency (histogram) distribution of Tmrt values across the whole district over different times of the day.The results indicate that shade provision by urban geometry reduces pedestrian heat stress from extreme to moderate levels in the morning (until 12:00 local time) and afternoon (starting from 16:00). In the time window from 13:00 to 15:00, urban geometry has negligible impact due to high solar elevations, while trees shades significantly reduce heat stress from beyond extreme to moderate levels.Based on the results, we generated a cumulative heat stress frequency map that can be used as a practical tool to plan district-scale shading interventions enabling acceptable thermal conditions across the whole urban area.

The combined effect of global warming and urban heat island (UHI) is leading to a sharp increase in building cooling consumption and outdoor thermal stress in cities. Building retrofits interventions using nature-based solutions (NBS) such as green facades (GF) and green roofs (GR) can reverse this vicious heat cycle. GFs and GRs reduce the radiant heat transfer from the building envelope to the interior, while also reducing the external radiant temperatures, with positive impacts on both the indoor and the outdoor environments. For district scale applications, they can mitigate the local UHI intensity, with positive returns in terms of building cooling demand. The positive effect of GF and GR on the indoor thermal conditions of buildings has been widely studied, as well as their positive effect on the urban microclimate. However, most of the studies focused on only one of the two domains, lacking a comprehensive assessment of the global indoor-outdoor cooling potential.This work proposes a simulation framework to quantify the global cooling potential of NBS applied to building retrofits at the district scale, considering their dual impact on the indoor and outdoor thermal environment. The approach is applied to the UPC University Campus of Terrassa (Barcelona, Spain), considering a deep retrofit scenario with GF and GR applied to all buildings. ENVImet is used to simulate the outdoor microclimate conditions of the campus in the current and retrofit scenarios. The ENVImet outputs are used to morph the weather files for use in EnergyPlus simulations of a representative building, including simplified GR and GF models. The improvement in indoor operative temperature and outdoor mean radiant temperature are used as performance indicators.The results provide an assessment of the potential for district-scale building retrofits using NBS to improve urban thermal comfort while contributing to the transition towards climate neutral cities.

We present unprecedented datasets of current and future projected weather files for building simulations in 15 major cities distributed across 10 climate zones worldwide. The datasets include ambient air temperature, relative humidity, atmospheric pressure, direct and diffuse solar irradiance, and wind speed at hourly resolution, which are essential climate elements needed to undertake building simulations. The datasets contain typical and extreme weather years in the EnergyPlus weather file (EPW) format and multiyear projections in comma-separated value (CSV) format for three periods: historical (2001–2020), future mid-term (2041–2060), and future long-term (2081–2100). The datasets were generated from projections of one regional climate model, which were bias-corrected using multiyear observational data for each city. The methodology used makes the datasets among the first to incorporate complex changes in the future climate for the frequency, duration, and magnitude of extreme temperatures. These datasets, created within the IEA EBC Annex 80 “Resilient Cooling for Buildings”, are ready to be used for different types of building adaptation and resilience studies to climate change and heatwaves.

Climate change and urban heat islands increase the use of mechanical cooling in buildings. The urban heat island (UHI) is responsible for a significant increase in the cooling load of buildings in Mediterranean cities. Furthermore, the use of air conditioning (AC) in buildings generates waste heat into the urban canopy thereby exacerbating the urban heat island (UHI) intensity. A significant increase in city-scale energy consumption and anthropogenic heat generation is expected due to climate change and the broader use of AC in buildings. This study investigates the combined effect of global warming and urban heat island intensity on the future building cooling demand. The analysis will be carried out using the standalone urban energy/climate model (SUECM) and future weather estimates.