Increase In Albedo Research Articles

Arctic sea‐ice export as a mechanism for cold climate events during the last deglaciation

ABSTRACTRecently it was proposed that a sudden drainage of accumulated Arctic sea ice could have caused cold climate events during the last deglaciation. To explore this mechanism, we performed numerical experiments with an atmosphere–ocean–sea ice model. In these experiments, the impact of a large flush of Arctic sea ice was compared to a reference glacial state of the climate. In our results, the sea ice flush produces a major surface freshening of the North Atlantic Ocean and a 17% weakening of the strength of the Atlantic Meridional Overturning Circulation. Together with an increase in surface albedo, this weakening in ocean circulation leads to a cooling over the North Atlantic, extending to the downwind continents. Compared to our reference glacial state, the cooling reaches 5°C and lasts about 80 years. This climate anomaly is similar in magnitude and duration to relatively short cooling events during the last deglaciation, such as the Older Dryas, the Inter‐Allerød cold period and the Preboreal Oscillation. We thus conclude that the sea‐ice flush mechanism is consistent with the occurrence of such cooling events in the North Atlantic region. However, longer cooling events such as the Younger Dryas would require additional mechanisms.

Nonlinear changes in urban heat island intensity, urban breeze intensity, and urban air pollutant concentration with roof albedo

This study systematically examines how the urban heat island (UHI) and urban breeze circulation (UBC) respond to an increase in roof albedo (αr) and its influence on urban air pollutant dispersion. For this, idealized ensemble simulations are performed using the Weather Research and Forecasting (WRF) model. The increase in αr from 0.20 to 0.65 decreases the UHI intensity, UBC intensity, and urban planetary boundary layer (PBL) height in the daytime (from 1200 to 1700 LST) by 47%, 36%, and 6%, respectively. As both UBC intensity and urban PBL height decrease, the daytime urban near-surface passive tracer concentration increases by 115%. The daytime UHI intensity, UBC intensity, and urban tracer concentration nonlinearly change with αr: For 0.10 ≤ αr < 0.80, the rates of changes in the UHI intensity, UBC intensity, and urban tracer concentration with αr overall increase as αr increases. For αr ≥ 0.80, the daytime roof surface temperature is notably lower than the daytime urban near-surface air temperature, the UHI intensity, UBC intensity, and urban tracer concentration very slightly changing with αr. This study provides insights into the associations between changes in roof surface temperature and roof surface energy fluxes with αr and those in UHI intensity.

Assessing the impact of artificial geotextile covers on glacier mass balance and energy fluxes

As global warming accelerates, leading to the retreat of glaciers, the effectiveness of artificial coverings, in particular geotextiles, in reducing glacier ablation has emerged as a topic of increasing concern. Nevertheless, a critical gap in knowledge persists regarding the specific physical processes involved in the mitigation provided by these coverings. This study explores the underlying mechanisms that govern the interaction through field observations and COSIPY model simulations at Bailanghe Glacier No. 21 in the Qilian Mountains from 26 June to 17 September 2023. It compares covered and uncovered areas to evaluate differences in mass and energy balance fluxes. It was discovered that geotextiles could decrease ice melt by up to 1000 mm w.e. in comparison to the surface of glaciers without cover, primarily because of a 23% increase in albedo compared to ice, leading to a decrease in net short-wave radiation and available melt energy. The effect of covering the entire glacier with a geotextile, which has varying albedo properties, was also simulated. It was found that, with every 5% increase in the albedo of the geotextile, ablation was reduced by 10%‒25%, resulting in a decrease in ice volume loss of approximately 2.5 × 105 m3. While artificially covering glaciers can reduce ablation rates, it faces challenges such as high costs, environmental risks, and issues with replicability. Ultimately, this study aims to analyze the feasibility of glacier coverage from a mechanistic perspective for glacier management amidst ongoing climate change.

Solar Energy Received on Flat-Plate Collectors Fixed on 2-Axis Trackers: Effect of Ground Albedo and Clouds

This study investigates the performance of isotropic and anisotropic diffuse models to estimate the total solar energy received on flat-plate collectors fixed on dual-axis trackers. These estimations are applied at twelve sites selected in both hemispheres with different terrain and environmental conditions. The diffuse (or transposition) models used in this study are the isotropic Liu-Jordan (L&amp;J), Koronakis (KOR), Badescu (BAD), and Tian (TIA), and the anisotropic Hay (HAY), Reindl (REI), Klucher (KLU), Skartveit and Olseth (S&amp;O), and Steven and Unsworth (S&amp;U). These models were chosen because of their simplicity in the calculations and minimum number of input values. The results show that a single transposition model is not efficient for all sites; therefore, the most appropriate models are selected for each site under all, clear, intermediate, and overcast conditions in skies. On the other hand, an increase in the ground albedo in the vicinity of the solar installation can increase the annual inclined solar availability on a two-axis tracker by at least 9% on average. Further, a linear dependence of the annual inclined solar energy on the variation of the ground albedo was found. Also, a linear relationship exists between the annual diffuse-fraction and cloud-modification factor values at the 12 sites.

The Effects of Summer Snowfall on Arctic Sea Ice Radiative Forcing

AbstractSnow is the most reflective natural surface on Earth. Since fresh snow on bare sea ice increases the surface albedo, the impact of summer snow accumulation can have a negative radiative forcing effect, which would inhibit sea ice surface melt and potentially slow sea‐ice loss. However, it is not well known how often, where, and when summer snowfall events occur on Arctic sea ice. In this study, we used in situ and model snow depth data paired with surface albedo and atmospheric conditions from satellite retrievals to characterize summer snow accumulation on Arctic sea ice from 2003 to 2017. We found that, across the Arctic, ∼2 snow accumulation events occurred on initially snow‐free conditions each year. The average snow depth and albedo increases were ∼2 cm and 0.08, respectively. 16.5% of the snow accumulation events were optically thick (&gt;3 cm deep) and lasted 2.9 days longer than the average snow accumulation event (3.4 days). Based on a simple, multiple scattering radiative transfer model, we estimated a −0.086 ± 0.020 W m−2 change in the annual average top‐of‐the‐atmosphere radiative forcing for summer snowfall events in 2003–2017. The following work provides new information on the frequency, distribution, and duration of observed snow accumulation events over Arctic sea ice in summer. Such results may be particularly useful in understanding the impacts of ephemeral summer weather on surface albedo and their propagating effects on the radiative forcing over Arctic sea ice, as well as assessing climate model simulations of summer atmosphere‐ice processes.

Impact of Increasing Albedo on Choosing the Optimal Tilt Angle to Optimize PV Systems : Case Study

The amount of irradiation energy that is produced by reflecting one's surroundings is measured using albedo. The amount of albedo is affected by factors such as time, position, geometry, and meteorological conditions. The albedo value responds to changes in any of the characteristics described above, even if those changes are just slight. Because of this, modelling albedo can be difficult. This paper applied the optimum tilt angle at 31° with a constant albedo 0.2 for location in Al-Furat Al-Awsat Technical University - at latitude 32°03'30.6" North and longitude 44°24'13.3" East. After treating the surface on which the PV system is installed with white Portland cement, the surface albedo will change to (0.87); the increase in albedo leads to an increase in reflected radiation from the ground on PV panels then increase in the power output, also the results shown to reaching the maximum value of the solar irradiation hitting the PV panels to get maximum value of power output with albedo 0.87 in this location, optimum tilt angle will change to be 42o instated of 31o. This study proved that when the albedo of the surface on which the system is installed changes, so does the optimal tilt angle.

Numerical assessment of changes in land–atmosphere interactions during the rainy season in South America using an updated vegetation map

AbstractLand Use and Land Cover Change (LULCC) is a key driver of changes in land–atmosphere interactions, playing an essential role in climate and weather patterns in South America (SA). This study used a modelling approach to assess the land–atmosphere changes introduced by LULCC over the Brazilian territory. Numerical experiments of early (2006), neutral (2004) and late (2008) rainy season onset years were performed in the Integrated BIosphere Simulator (IBIS) to assess the land‐surface parameters, and in Brazilian Atmospheric Model (BAM) to assess the atmospheric variables. The models were run with a natural (NAT) vegetation map and an updated (UP) vegetation map, which incorporated realistic Brazil deforestation up to the early 2000s. The differences between the two maps were particularly larger over 25°–15°S and 50°–40°W, where the Atlantic Forest and Cerrado biomes were replaced by pasture. IBIS experiments showed that over the area of larger LULCC there was an increase in albedo of up to 8% while reductions in net radiation, surface heat fluxes, surface temperature and surface roughness were noticed. Land–atmosphere feedbacks assessed with BAM experiments showed that LULCC contributed to a drier and colder (stable) atmosphere over central‐east SA that opposes the necessary conditions for the rainy season onset. The changes included increases in surface pressure and low‐level wind associated with reductions in 2 m temperature and surface roughness. These changes contributed to decrease the cloud formation and less precipitation in all three rainy season onset years, but particularly in the late rainy season onset year during September–October–November (SON). The atmospheric changes induced by LULCC show a pattern of dry atmosphere (reduced precipitation), similar to those of late onset years, and indicate that LULCC enhances the late rainy season onset condition over central‐east SA. Additionally, this study highlights the importance of considering up‐to‐date vegetation maps because these changes significantly affect both surface and atmospheric variables.

Accounting for the effect of aerosols in GHGSat methane retrieval

Abstract. GHGSat comprises a constellation of satellites with high spatial and spectral resolution that specialize in monitoring methane emissions at 1.65 µm. This study investigates the ability to accurately retrieve both the methane mixing-ratio enhancement (ΔXCH4) and the aerosol optical depth (AOD) simultaneously from simulated GHGSat observations that incorporate angle-dependent scattering information. Results indicate that the sign of the ΔXCH4 bias when neglecting aerosols changes from negative to positive as surface albedo increases, which is consistent with previous studies. The bias in ΔXCH4 is most pronounced when AOD is not simultaneously retrieved, ranging from −3.0 % to 6.3 % with an AOD of 0.1, a 60° solar zenith angle, and a surface albedo of 0.2 for the nadir-only retrieval. Using multiple satellite viewing angles during the GHGSat observation sequence with a scattering angle ranging from 100 to 140°, the study shows that the mean bias and standard deviation of ΔXCH4 are within 0.3 % and 2.8 % relative to the background. The correlation between simultaneously retrieved ΔXCH4 and AOD shifts from being positive to negative as surface albedo increases and the aerosol asymmetry factor decreases, signifying a transition of the dominant aerosol effect from aerosol-only scattering to aerosol–surface multiple scattering. The variety of scattering angle ranges has little impact on the performance of the multi-angle viewing method. This study improves the understanding of the impact of aerosols on the GHGSat ΔXCH4 retrieval and provides guidance for improving future GHGSat-like point-source imagers.

Arctic Sea Ice Albedo Estimation from Fengyun-3C/Visible and Infra-Red Radiometer

The sea ice albedo can amplify global climate change and affect the surface energy in the Arctic. In this paper, the data from Visible and Infra-Red Radiometer (VIRR) onboard Fengyun-3C satellite are applied to derive the Arctic sea ice albedo. Two radiative transfer models, namely, 6S and FluxNet, are used to simulate the reflectance and albedo in the shortwave band. Clear sky sea ice albedo in the Arctic region (60°~90°N) from 2016 to 2019 is derived through the physical process, including data preprocessing, narrowband to broadband conversion, anisotropy correction, and atmospheric correction. The results are compared with aircraft measurements and AVHRR Polar Pathfinder-Extended (APP-x) albedo product and OLCI MPF product. The bias and standard deviation of the difference between VIRR albedo and aircraft measurements are −0.040 and 0.071, respectively. Compared with APP-x product and OLCI MPF product, a good consistency of albedo is shown. And analyzed together with melt pond fraction, an obvious negative relationship can be seen. After processing the 4-year data, an obvious annual trend can be observed. Due to the influence of snow on the ice surface, the average surface albedo of the Arctic in March and April can reach more than 0.8. Starting in May, with the ice and snow melting and melt ponds forming, the albedo drops rapidly to 0.5–0.6. Into August, the melt ponds begin to freeze and the surface albedo increases.

Impact of Wildfires on Land Surface Cold Season Climate in the Northern High-Latitudes: A Study on Changes in Vegetation, Snow Dynamics, Albedo, and Radiative Forcing

Anthropogenic climate change is increasing the occurrence of wildfires, especially in northern high latitudes, leading to a shift in land surface climate. This study aims to determine the predominant climatic effects of fires in boreal forests to assess their impact on vegetation composition, surface albedo, and snow dynamics. The influence of fire-induced changes on Earth’s radiative forcing is investigated, while considering variations in burn severity and postfire vegetation structure. Six burn sites are explored in central Alaska’s boreal region, alongside six control sites, by utilizing Moderate Resolution Imaging Spectroradiometer (MODIS)-derived albedo, Leaf Area Index (LAI), snowmelt timing data, AmeriFlux radiation, National Land Cover Database (NLCD) land cover, and Monitoring Trends in Burn Severity (MTBS) data. Key findings reveal significant postfire shifts in land cover at each site, mainly from high- to low-stature vegetation. A continuous increase in postfire surface albedo and negative surface shortwave forcing was noted even after 12 years postfire, particularly during the spring and at high-severity burn areas. Results indicate that the cooling effect from increased albedo during the snow season may surpass the warming effects of earlier snowmelt. The overall climate impact of fires depends on burn severity and vegetation composition.

Indigenous lands and conservation units slow down non-GHG climate change in the Cerrado-Amazon ecotone

Preserving tropical forests by avoiding deforestation and forest degradation is essential for maintaining ecosystem services. Brazilian Conservation Units (CUs) and Indigenous Lands (ILs) have effectively prevented deforestation and supported climate regulation. However, these protected areas face increasing threats from forest fires and droughts across the Amazon and Cerrado biomes. This study assesses how disturbances affect climate regulating factors (surface temperature (LST), evapotranspiration (ET), and albedo) in Mato Grosso state, among different land uses (CUs, ILs, and multiple-use areas - MUs). To do so, we analyzed satellite data collected between 2001 and 2020. Results showed that MUs (outside protected areas) had lower ET (∼10%), higher daytime LST (∼1.5 °C), and higher albedo (∼10%) than CUs and ILs in both biomes in 2001. Over the study period, MUs experienced a greater increase in LST (Amazon: ∼1.4 °C; Cerrado: ∼1.1 °C) and albedo (Amazon: ∼6%; Cerrado: ∼3%) compared to protected areas, regardless of the biome. In contrast, ILs and CUs showed smaller mean changes in LST (∼0.2 °C), ET (∼1.3%), and albedo (∼1.3%). These changes were associated with native vegetation loss, forest fires, and water stress. Our results highlight the important role of protected areas in maintaining climate stability, with higher ET, lower LST, and lower albedo than other land uses. However, the long-term preservation of these services within protected areas depends on interventions in surrounding regions, particularly in the Amazon. Protecting and restoring these natural ecosystems is key for safeguarding ecosystem services and climate regulation in tropical regions.

On the energy impact of cool roofs in Dubai

Urban warming can significantly increase the energy demand for building cooling. As temperatures rise, buildings require additional energy for air conditioning, which can lead to higher electricity demand and increased greenhouse gas emissions. This can create a positive feedback loop, as increased energy demand leads to increased waste heat and further exacerbates the urban warming effect. To solve this issue, this study integrates high-resolution meteorological data from the Weather Research and Forecasting coupled with Single Layer Urban Canopy Model (WRF/SLUCM) into CitySim for the first time to evaluate the building energy demands at various building types in Dubai metropolis. Examining how cool materials reduced cooling loads was achievable utilizing modified albedo in Dubai's downtown buildings. An increase of urban albedo from 0.2 to 0.8 significantly lowers the urban heating effect, as well as the building cooling needs. The study shows that for albedo scenario 0.8, Low-rise residential buildings experienced cooling load reductions of about 13.1 kWh/m2 and 6 kWh/m2 for buildings without insulation and those with insulation, respectively, compared to the base case. Additionally, high-rise residential buildings saw cooling load reductions ranging from 7.7 kWh/m2 to 11.7 kWh/m2 for buildings without insulation and a cooling load reduction of 3.6 kWh/m2 to 5.4 kWh/m2 for insulated buildings. This study provides a tool for regulating the energy impact of cool roofs in different urban settings using energy simulation, which could help policymakers control the energy needs in subtropical desert urban environments.

Source-specified atmospheric age distribution of black carbon and its impact on optical properties over the Yangtze River Delta

Black carbon (BC) exerts a profound and intricate impact on both air quality and climate due to its high light absorption. However, the uncertainty in representing the absorption enhancement of BC in climate models leads to an increased range in the modeled aerosol climate effects. Changes in BC optical properties could result either from atmospheric aging processes or from variations in its sources. In this study, a source-age model for identifying emission sources and aging states presented by University of California at Davis/California Institute of Technology (UCD/CIT) was used to simulate the atmospheric age distribution of BC from different sources and to quantify its impact on the optical properties of BC-containing particles. The results indicate that regions with greater aged BC concentrations do not correspond to regions with higher BC emissions due to atmospheric transport. High concentrations of aged BC are found in northern Yangtze River Delta (YRD) regions during summer. The chemical compositions of particles from different sources and with different atmospheric ages differ significantly. BC and primary organic aerosols (POA) are dominating in Traffic-dominated source while other components dominate in Industry-dominated source. As the atmospheric age increases, the mass fraction of secondary inorganic aerosols rises. Compared to the original model, the simulated mass absorption cross section of BC particles in the source-age model decreases while the single scattering albedo increases. This compensates for ~11 % of the overestimation of the simulated BC direct radiative forcing. Our study highlights that incorporating atmospheric age and source information into models can greatly improve the estimation of optical properties of BC-containing particles and deepen our understanding of their climate effects.

Winter cover cropping increases albedo and latent heat flux in a Texas High Plains agroecosystem

AbstractWinter cover crops represent a land cover change that may sequester carbon in the soil and improve agricultural sustainability. Their adoption may also change the Earth's radiative balance and result in biophysical feedbacks to climate through alterations in albedo and latent heat fluxes. Understanding the mechanisms underlying these alterations to the radiative balance is important for making reliable future climate projections. However, data on cover crop biophysics are limited, requiring models to rely on data from summer plants for parameterization, likely biasing predictions. To address this gap, we measured the albedo and stomatal conductance of two summer crops and three winter crops on farms in the High Plains region of Texas. We also established a winter cover crop field experiment with two cover crops and fallow fields to estimate the change in albedo and latent heat flux that results from a switch to winter cover cropping. We found that albedo was significantly higher in winter‐like conditions than in summer‐like conditions due to an increase in plant albedo and a reduction in leaf area index. The albedo of winter cover crops was higher than the soil albedo, resulting in an increase in top‐of‐atmosphere reflected radiation of 7%–14% when converting from fallow fields to winter cover cropped fields. There was an additional cooling effect through doubling of the estimated latent heat flux caused by the presence of cover crops. The combined changes in albedo and latent heat resulted in a change in the surface energy balance that is associated with an overall cooling effect of winter cover crops on surface atmospheric temperatures. While this effect is likely to be region‐specific, these results strongly indicate that winter cover crops alter the surface albedo and latent heat flux of agricultural fields and provide a direct cooling effect in the High Plains region of Texas.

Polarimetry of Didymos–Dimorphos: Unexpected Long-term Effects of the DART Impact

We have monitored the Didymos–Dimorphos binary system in imaging polarimetric mode before and after the impact from the Double Asteroid Redirection Test mission. A previous spectropolarimetric study showed that the impact caused a dramatic drop in polarization. Our longer-term monitoring shows that the polarization of the post-impact system remains lower than the pre-impact system even months after the impact, suggesting that some fresh ejecta material remains in the system at the time of our observations, either in orbit or settled on the surface. The slope of the post-impact polarimetric curve is shallower than that of the pre-impact system, implying an increase in albedo of the system. This suggests that the ejected material is composed of smaller and possibly brighter particles than those present on the pre-impact surface of the asteroid. Our polarimetric maps show that the dust cloud ejected immediately after the impact polarizes light in a spatially uniform manner (and at a lower level than pre-impact). Later maps exhibit a gradient in polarization between the photocentre (which probes the asteroid surface) and the surrounding cloud and tail. The polarization occasionally shows some small-scale variations, the source of which is not yet clear. The polarimetric phase curve of Didymos–Dimorphos resembles that of the S-type asteroid class.

The influence of hemispherical albedo on the dynamics of cometary particles

ABSTRACT This paper presents a new approach to determining the dimensions of particles that can be lifted to a coma by the sublimation flux of water ice. Due to the diverse colour of the cometary surfaces, in the presented calculations we take into account the influence of the reflectance coefficient (hemispherical albedo) on the size of particles lifted from the surface of the nucleus. A Cary 5000 spectrometer was used to measure hemispherical albedo. Spectroscopic measurements used dust particles that consisted of pure silicate or were a mixture of pure silicate and organic compounds such as charcoal, soot, and ash. In addition, these admixtures acted as a means of darkening the tested sample. Depending on the colour of the sample and the wavelength, the measured value of hemispherical albedo oscillated in the range from 4.93 per cent to 48.65 per cent. A thermodynamic model of cometary matter emission was developed based on the results of hemispherical albedo measurements. The performed numerical simulations show that the temperature decreases with the increase of the hemispherical albedo, which translates into the sublimation flux and the dynamics of the dust-ice particles present on the surface of the cometary nucleus. Taking into account the extreme values of the hemispherical albedo, the differences in the size of particles carried away from the surface of the nucleus are in the order of centimeters.

Cool roofs boost the energy production of photovoltaics: Investigating the impact of roof albedo on the energy performance of monofacial and bifacial photovoltaic modules

Photovoltaics (PVs) provide clean and affordable energy contributing to the decarbonisation of the energy sector. High surface temperature of the PV modules reduces their efficiency and the corresponding energy production and increases the sensible heat released to the atmosphere contributing to urban overheating. For roof mounted PVs, increase of the roof albedo helps to decrease the surrounding ambient temperature, raises the efficiency of the PVs and increases the reflected solar radiation received by the modules. Numerous studies have assessed the impact of increased roof albedo on the energy yield of the monofacial and bifacial PVs for given installation characteristics and specific climatic conditions. There is a serious need to collect, analyse, compare, and parameterize the existing information in order to provide more global and holistic knowledge to the PVs industry. We have analysed 13 and 57 case studies reporting the impact of modified roof albedo on the energy yield of monofacial and bifacial PV modules, respectively. It is concluded that, on average, increasing the roof albedo by 0.1 contributes to enhance the energy production of monofacial and bifacial PV modules by 0.7% and 4.55% respectively while delivering important co-benefits to urban heat mitigation. Parametric relations between the potential increase of the roof albedo and the increase of the annual energy yield are proposed for both monofacial and bifacial PV modules. The impact of the geographic and installation parameters on the energy production of the modules is analysed and discussed. The results of such a study could help to identify the optimal roof albedo for maximizing energy performance and reducing energy costs.

Observed and simulated local climate responses to tropical deforestation

Tropical deforestation has local and regional effects on climate, but the sign and magnitude of these effects are still poorly constrained. Here we used satellite observations to evaluate the local land surface temperature and precipitation response to tropical deforestation in historical simulations from 24 CMIP6 models. We found tropical forest loss leads to an observed local dry season warming and reduced wet and dry season precipitation across the range of scales (0.25°-2°) analysed. At the largest scale analysed (2°), we observed a warming of 0.018 ± 0.001 °C per percentage point of forest loss (°C %−1), broadly captured in the multi-model mean response of 0.017 ± 0.005 °C %−1. The multi-model mean correctly simulates reduced precipitation due to forest loss in the dry season but simulates increased precipitation due to forest loss in the wet season, opposite to the observed response. We found that the simulated dry season surface temperature and precipitation changes due to forest loss depend on the simulated surface albedo change, with less warming and less drying in models with greater increases in surface albedo due to forest loss. Increased recognition of the local and regional climate benefits of tropical forests is needed to support sustainable land use policy.

Application of the novel satellite calibrated method “Radiative Forcing Meter” on a high albedo test facility for CO2 compensation

The increase of terrestrial albedo may be considered a key strategy to mitigate global warming, since it produces a reduction of the radiative forcing (RF). The RF concept, as defined by IPCC, is used in literature for calculations of the CO2 compensation due to albedo increase, which can be achieved by the development of high-albedo solutions (cool materials, retro-reflective materials, green infrastructures, etc.). The authors have previously proposed a new procedure, called RF-meter, to measure the continuous time history of the RF due to an albedo increase (RFΔα) and so to calculate the related CO2 offset potential by high-albedo solutions. RF-meter procedure is based on the continuous albedo measurements at ground level and discrete satellite calibration. The proposed method is tested on a high-albedo surface (HAS) of 900 m2 treated with a high-reflective paint installed on the roof of CIRIAF building, University of Perugia, Italy. The experimental field is equipped with an albedometer, a weather station and a Calculus Unit. The measured data are elaborated by the Calculus Unit to calculate the RF time history and the compensated CO2. Data from albedo monitoring exhibited that albedo of HAS was always higher than albedo before the treatment (α0) and the average Δα is equal to 0.3. The calibration procedure allows to reduce the errors on RFΔα calculation. The maximum difference between albedo values from albedometer and satellite measurements resulted equal to 3.9%. Results from the Calculus Unit showed an amount of CO2 compensated by HAS equal to 73 kgCO2eq/m2.

The effect of facade materials and coatings on urban heat island mitigation and outdoor thermal comfort in hot semi-arid climate

High urban temperature is generally associated with negative effects on building energy consumption, outdoor thermal comfort, air quality, and human health. Then it is necessary to find strategies to reduce urban heat island and improve outdoor thermal comfort. This research investigates and classifies facade coatings and materials with regards to urban heat island effect in hot semi-arid climate of Shiraz. The surface temperature of 20 common and modern building facade materials during two periods for five days and their effect on outdoor air temperature is investigated through field measurement. Additionally, to study the effect of each material on urban heat island and thermal comfort index, Physiological Equivalent Temperature (PET) of a neighborhood in Shiraz was simulated with ENVI-met software on June 22. The results show that during the day under direct sunlight, the living wall has the lowest surface and air temperatures, and as the nearby air temperature increases during the night, it lowers the temperature fluctuations both during the day and night. Materials with high albedo increase the Mean Radiant Temperature and PET index despite their lower surface temperature. Materials with high thermal mass and low emissivity have lower temperature. The living wall has the lowest PET index, indoor and outdoor surface temperature during the day. It can also result in 2 °C reduction of air temperature.