The urban climate is highly influenced by its building geometry, material characteristics, street orientation and high fraction of impermeable surfaces. All of these influence the microclimate and the resulting outdoor thermal comfort. Mean radiant temperature (Tmrt) is often used as an estimator for heat exposure as it is one of the most important variables governing outdoor human thermal comfort on clear, calm and warm days. The highest values of Tmrt are commonly found in front of sunlit facades where a human is exposed to high levels of direct and reflected shortwave radiation from the sun, as well as high levels of longwave radiation emitted from surrounding sunlit walls. As a consequence, outdoor thermal comfort modelling requires accurate simulation of wall surface temperatures (Ts).The aim of this study is to present a step heating approach for calculating wall Ts in the SOlar and LongWave Environmental Irradiance Geometry model (SOLWEIG) and quantify how it influences Tmrt. This method requires information on material characteristics, i.e. specific heat capacity, density, thermal conductivity, albedo and thickness of the outer layer of the wall, as well as radiation balance at the wall surface, and ambient air temperature. Simulated Ts is compared to observed Ts of two white walls (albedo = 0.5) in Gothenburg, Sweden; one wooden wall and one plaster brick wall. The simulations show high agreement with the 15 394 observations, with R2=0.93 and RMSE = 2.09 degrees C for the wooden wall and R2=0.94 and RMSE = 1.94 degrees C for the plaster brick wall. For the walls presented here, this new parameterization scheme results in differences in Tmrt of up to 2.5 degrees C compared to the previous version of SOLWEIG.With this new approach, SOLWEIG can be used to evaluate the effect of building materials on outdoor thermal comfort. The speed and accuracy of this approach suggests that it also could be applied in other areas where Ts of walls are important, for example building energy models and urban energy balance models.

In the context of the accelerating impacts of climate change on permafrost landscapes, this study employs UAV (Unmanned Aerial Vehicle) LiDAR technology to investigate seasonal terrain changes in palsas – mounds of frozen peat – since traditional remote sensing methods have struggled to capture the full dynamics of these landforms. We investigated two tall (4–5 m tall) palsas in Sweden's largest palsa mire complex, where we performed five field campaigns between September 2022 and September 2023 to track intra-annual frost heave and thaw subsidence. Our approach allowed us to create digital terrain models (DTMs) from high density point clouds (>1,000 points/m²) and analyze elevation changes over time. We found that both palsas heaved 0.15 m from September to April and subsided back to their height from the previous year, or slightly below, over the course of the following summer. At one of the palsas, we observed notable lateral degradation over the study period in a 300 m2 area, with 0.5–2.0 m height loss, likely initiated during the preceding warm and wet summer months. Part of this degradation occurred between September 2022 and April 2023, suggesting that the degradation of these palsas is not limited to the summer months. Our study shows the value of using UAV LiDAR for understanding how permafrost areas are changing. It helps in tracking the ongoing effects of climate change and highlights palsa dynamics that would not be captured by annual measurements only.

A robust representation of the radiative properties in complex urban settings is important for accurate estimations of radiant load. Here, we present a new parameterization scheme in the SOlar and LongWave Environmental Irradiance Geometry (SOLWEIG) model that partitions the upper hemisphere into 153 patches. Partitioning of the upper hemisphere enables determination if longwave irradiance originates from the sky, vegetation, sunlit building surfaces, or shaded building surfaces from each patch. Furthermore, a model for anisotropic sky longwave irradiance where emissivity increases with zenith angle is included. Comparisons between observations and simulations show high correlation, with R 2 and RMSE for T mrt of 0.94 and 4.6 °C, respectively, and R 2 and RMSE for longwave radiation of 0.89 and 14.1 Wm −2 , respectively. Simulations show that mean radiant temperature ( T mrt ) can be up to 1.5 °C higher with an anisotropic sky compared to a uniform sky as an effect of higher radiant load on the vertical of a human when sky longwave irradiance increases with zenith angle. In comparisons of simulated T mrt with the new parameterization and old parameterization schemes, previously overestimated T mrt under trees (high sky obstruction, sky view factor (SVF) < 0.3) can be decreased by up to 3 °C from more realistic estimations using the patches. Moreover, T mrt close to sunlit walls (SVF ~ 0.5) is increased by up to 2–3 °C from increased exposure to sunlit surfaces. Concluding, anisotropic sky longwave radiation and directionality of longwave radiation from different sources are important in estimations of T mrt of humans in outdoor settings.

The Vissátvuopmi palsa complex (N 68°74′50′′, E 21°11′30”) is the largest coherent palsa complex in Sweden (ca 274 ha). Aerial photo-interpretation over an area covered by plateau palsas showed a 30% decline in lateral area -- from ca 70 to 49 ha -- that occurred between 1955 to 2016 (Olvmo et al., 2020). Within Vissátvuopmi, we have more closely studied two single palsas, one dome-shaped and one ridge-shaped, for changes in extent, height and vegetation composition. Manual interpretation of aerial photography between 1955 and 2016 show lateral degradation of 35% and 54% for the dome and ridge palsas, respectively. Since 2018 we have monitored the palsas using images from drones as well as analysis of Planet Dove and Sentinel-2 satellite imagery. Photogrammetry is used to produce orthophotos as well as digital surface models (DSMs) from the drone images, and compared to earlier LiDAR and aerial photo DSMs, to study lateral and vertical degradation. The drone-generated DSMs from 2018, 2019 and 2020 show further lateral degradation of the two large palsas. In 2020 a rapid change in vegetation composition was seen on the dome-shaped palsa, where a 250 m2 area of Betula nana and Empetrum hermaphroditum transitioned to lichen. This vegetation change could be seen in spectral data from both drone and satellite platforms. The future development of this palsa, monitored annually using both fine and medium spatial resolution data, will give insight into the timing and signs of the individual palsas in stages of degradation.

BACKGROUND:The Wet-Bulb Globe Temperature (WBGT) index is a common tool to screen for heat stress for sporting events. However, the index has a number of limitations. Rational indices, such as the physiological equivalent temperature (PET) and Universal Thermal Climate Index (UTCI), are potential alternatives.AIM:To identify the thermal index that best predicts ambulance-required assistances and collapses during a city half marathon.METHODS:Eight years (2010-2017) of meteorological and ambulance transport data, including medical records, from Gothenburg's half-marathon were used to analyse associations between WBGT, PET and UTCI and the rates of ambulance-required assistances and collapses. All associations were evaluated by Monte-Carlo simulations and leave-one-out-cross-validation.RESULTS:The PET index showed the strongest correlation with both the rate of ambulance-required assistances (R2=0.72, p=0.008) and collapses (R2=0.71, p=0.008), followed by the UTCI (R2=0.64, p=0.017; R2=0.64, p=0.017) whereas the WBGT index showed substantially poorer correlations (R2=0.56, p=0.031; R2=0.56, p=0.033). PET stages of stress, match the rates of collapses better that the WBGT flag colour warning. Compared with the PET, the WBGT underestimates heat stress, especially at high radiant heat load. The rate of collapses increases with increasing heat stress; large increase from the day before the race seems to have an impact of the rate of collapses.CONCLUSION:We contend that the PET is a better predictor of collapses during a half marathon than the WBGT. We call for further investigation of PET as a screening tool alongside WBGT.

Substantial palsa degradation has occurred in Fennoscandia, which is considered to be driven by global climate change. Deeper understanding of the role of different climatic drivers on palsa decay, however, is lacking. We use meteorological data and aerial photographs from 1955 to 2016 to statistically identify the most important climatic drivers affecting changes in lateral-temporal palsa decay rates in the largest coherent palsa complex in Sweden, Vissátvuopmi. We show that wetter, warmer and shorter winters are the main causes of large and rapid changes in lateral-palsa extent since the mid-1950s. By analyzing meteorological data from the 1880s to present, we show that average annual temperature conditions have been unfavourable for palsas for more than a century and average annual precipitation conditions have been unfavourable since the 1940s. The decay rates have likely been amplified over the past 50-60 years, and in particular over the most recent decades, due to the combined effect of adverse air temperature and precipitation conditions. Palsa loss is expected to continue, most likely at a higher rate than today, with serious ecological impacts as a consequence.

During clear weather conditions the main part of the shortwave irradiance derives from sun direct-beam radiation. However, part of the shortwave radiation also originates from all-sky diffuse radiation (D), with a large part being circumsolar in origin. Many radiation models considers the sky as isotropic when estimating D. Here we implement an anisotropic model for D into the SOLWEIG model to examine the spatial patterns of D in a built-up environment, as well as its influence on mean radiant temperature (T-mrt), a variable essential for estimating outdoor human thermal comfort. Comparisons between the anisotropic and the isotropic models indicates that the D in the isotropic model is overestimated in shaded areas and underestimated in areas close to sunlit walls. This is explained by the circumsolar origin of D during clear and semi-cloudy conditions and solar altitude. These over- and underestimations, consecutively, have implications for T-mrt, which can differ by up to 3 degrees C. The deviations in D thus signify the importance of using an anisotropic model when estimating D and T-mrt, especially since the areas with the highest reported radiant loads receive even more radiation considering an anisotropic diffuse sky, i.e. the hottest areas are even hotter than previously reported.

AbstractThe aim was to analyze the influence of weather conditions on medical emergencies in a half-marathon, specifically by evaluating its relation to the number of non-finishers, ambulance-required assistances, and collapses in need of ambulance as well as looking at the location of such emergencies on the race course. Seven years of data from the world’s largest half marathon were used. Meteorological data were obtained from a nearby weather station, and the Physiological Equivalent Temperature (PET) index was used as a measure of general weather conditions. Of the 315,919 race starters, 104 runners out of the 140 ambulance-required assistances needed ambulance services due to collapses. Maximum air temperature and PET significantly co-variated with ambulance-required assistances, collapses, and non-finishers (R2=0.65–0.92; p=0.001–0.03). When air temperatures vary between 15–29°C, an increase of 1°C results in an increase of 2.5 (0.008/1000) ambulance-required assistances, 2.5 (0.008/1000) collapses (needing ambulance services), and 107 (0.34/1000) non-finishers. The results also indicate that when the daily maximum PET varies between 18–35°C, an increase of 1°C PET results in an increase of 1.8 collapses (0.006/1000) needing ambulance services and 66 non-finishers (0.21/1000).

Cultivated and settlement areas were studied in a small area (14 km2) in South Wollo, Ethiopia, by aerial photos, satellite images, field observations and interviews. Areas for cultivation/rural settlement decreased a few per cent between 1958 and 2013. Cultivated land per household slowly decreased in 1958-2003 but in 2003-2013 the annual decrease was 3-4 times higher. New farm buildings are often built on cultivated land, and abandoned buildings areas return to cultivation. Rainwater harvesting ponds have increased the areas with perennial crops that are important as a source of income. Tin roofed buildings are signs of improved livelihood. Very small farm size and rain-dependent agriculture combined with climate variability make food security vulnerable. Landuse inventories including remote sensing and local knowledge would be a valuable approach to assess livelihood needs. Further, it should involve decision makers at different levels, but local agricultural extension officers may play a central role.

Present-day and projected future changes in mean radiant temperature, T (mrt) in one northern, one mid-, and one southern European city (represented by Gothenburg, Frankfurt, and Porto), are presented, and the concept of hot spots is adopted. Air temperature, T (a) , increased in all cities by 2100, but changes in solar radiation due to changes in cloudiness counterbalanced or exacerbated the effects on T (mrt). The number of days with high T (mrt) in Gothenburg was relatively unchanged at the end of the century (+1 day), whereas it more than doubled in Frankfurt and tripled in Porto. The use of street trees to reduce daytime radiant heat load was analyzed using hot spots to identify where trees could be most beneficial. Hot spots, although varying in intensity and frequency, were generally confined to near sunlit southeast-southwest facing walls, in northeast corner of courtyards, and in open spaces in all three cities. By adding trees in these spaces, the radiant heat load can be reduced, especially in spaces with no or few trees. A set of design principles for reducing the radiant heat load is outlined based on these findings and existing literature.

ABSTRACTA nocturnal cooling rate model (NOCRAM) to simulate nocturnal air temperature at urban sites is presented. The model is designed for urban planners, practitioners and researchers who demand meteorological information for urban planning and research applications. The model is based on the concept of nocturnal cooling, progressing in two distinct phases, i.e. site‐dependent cooling around sunset and site‐independent cooling from about 1 or 2 h after sunset until sunrise. Cooling rates are usually determined predominantly by prevailing weather conditions (i.e. clearness of the sky and wind speed), followed by maximum daily air temperature and by sky view factors. Second phase cooling is chiefly determined by sky clearness and wind speed. The findings and statistical results from the analysis of observational data during warm months (May–September) from Gothenburg, Sweden, as well as from past studies, were used. The model requires standard meteorological variables (i.e. wind speed, incoming short‐wave radiation, air temperature, relative air humidity, air pressure) at a reference station as well as geometrical information (i.e. the sky view factor of the site and the geographical co‐ordinates of the reference meteorological station). The model simulates the characteristic development of cooling rates in the two phases at open sites and built‐up sites with different sky view factors under a wide range of weather conditions in warm months. Using the modelled cooling rates, nocturnal air temperature is estimated easily with the accuracy of root mean square error (RMSE) ≤1.54 °C and R2 ≥0.78.

ABSTRACTThe aim of this study was to provide a better understanding of how vegetation and building geometry influence the spatial distribution of air temperature and nocturnal cooling rates (CR) in a high‐latitude city. Intra‐urban thermal variations were analysed in two seasons (May–September and November–March) and in different weather conditions (clear, calm and cloudy, windy) in Gothenburg, Sweden. Simultaneous air temperature measurements were conducted for 2 years (2012–2013) at ten fixed park and street sites characterized by varying type and amount of vegetation, building geometry, openness and surface cover. Several spatial characteristics, including sky view factor (SVF) as well as the cover and volume of buildings and trees, were calculated within circular areas of radii ranging from 10 to 150 m. Spatial characteristics were found to explain air temperature distribution in the studied area to a large extent throughout the day and year, in both clear, calm as well as cloudy, windy conditions. The highest correlations were found for weighted calculation areas accounting for the influence of both nearest (10 m) and wider (25–150 m) surroundings. Park sites remained cooler than built‐up areas, with the most pronounced cooling effect (0.8 °C) on clear, calm days of the warm season. The most important factor governing CR around sunset was SVF. However, on clear, calm nights of the warm season, they were also enhanced by vegetation, indicating the influence of evapotranspiration. Minimum night‐time air temperature was governed mostly by the presence of buildings. Within the street canyon, a daytime cooling and night‐time warming effect of a street tree was observed, particularly in the warm season. The study shows the importance of various spatial characteristics describing openness, amount of vegetation and building geometry in analysing intra‐urban variations in daytime and night‐time air temperature.

Urban areas are believed to affect temperature readings, thereby biasing the estimation of twentieth-century warming at regional to global scales. The precise effect of changes in the surroundings of meteorological stations, particularly gradual changes due to urban growth, is difficult to determine. In this paper, data from 10 temperature stations within 15 km of the city of Mainz (Germany) over a period of 842 days are examined to assess the connection between temperature and the properties of the station surroundings, considering (i) built/paved area surface coverage, (ii) population, and (iii) night light intensity. These properties were examined in circles with increasing radii from the stations to identify the most influential source areas. Daily maximum temperatures T-max, as well as daily average temperatures, are shown to be significantly influenced by elevation and were adjusted before the analysis of anthropogenic surroundings, whereas daily minimum temperatures T-min were not. Significant correlations (p < 0.1) between temperature and all examined properties of station surroundings up to 1000 m are found, but the effects are diminished at larger distance. Other factors, such as slope and topographic position (e.g., hollows), were important, especially to T-min. Therefore, properties of station surroundings up to 1000 m from the stations are most suitable for the assessment of potential urban influence on T-max and T-min in the temperate zone of central Europe.

An important ecosystem service provided by urban trees is the cooling effect caused by their transpiration. The aim of this study was to quantify the magnitude of daytime and night-time transpiration of common urban tree species in a high latitude city (Gothenburg, Sweden), to analyse the influence of weather conditions and surface permeability on the tree transpiration, and to find out whether tree transpiration contributed to daytime or nocturnal cooling. Stomatal conductance and leaf transpiration at day and night were measured on mature street and park trees of seven common tree species in Gothenburg: Tilia europaea, Quercus robur, Betula pendula, Acer platanoides, Aesculus hippocastanum, Fagus sylvatica and Prunus serrulata. Transpiration increased with vapour pressure deficit and photosynthetically active radiation. Midday rates of sunlit leaves ranged from less than 1 mmol m(-2) s(-1) (B. pendula) to over 3 mmol m(-2) s(-1) (Q. robur). Daytime stomatal conductance was positively related to the fraction of permeable surfaces within the vertically projected crown area. A simple estimate of available rainwater, comprising of precipitation sum and fractional surface permeability within the crown area, was found to explain 68% of variation in midday stomatal conductance. Night-time transpiration was observed in all studied species and amounted to 7 and 20% of midday transpiration of sunlit and shaded leaves, respectively. With an estimated night-time latent heat flux of 24 W m(-2), tree transpiration significantly increased the cooling rate around and shortly after sunset, but not later in the night. Despite a strong midday latent heat flux of 206 W m(-2), a cooling effect of tree transpiration was not observed during the day.

The urban heat island (UHI) and the intra-urban heat island (IUHI) are mainly nocturnal phenomena that develop through differences in cooling between urban and rural sites or between intra-urban sites of various types (Eliasson 1994; Runnalls and Oke 2000). These differences are a result of site characteristics such as building density, surface material, amount of vegetation and presence of anthropogenic heat (Oke 1987). It has been observed that nocturnal cooling progresses in two distinct phases (phase 1: site-dependent cooling around sunset, and phase 2: site-independent cooling from about one or two hours after sunset until sunrise) (Oke and Maxwell 1975; Upmanis et al. 1998; Holmer et al. 2007; Holmer et al. 2013). In this study, the temporal development of nocturnal cooling was investigated especially focusing on the two phases using observational data from Gothenburg, Sweden (Onomura et al. 2015). Based on the data analysis, a NOcturnal Cooling RAte Model (NOCRAM) was analytically developed to simulate nocturnal air temperature at urban sites using standard meteorological variables and sky view factor of the site. The model is evaluated with other datasets in the city and further applied to one built-up site with complex urban geometry in London UK.

We describe a new two-step modeling framework for investigating the impact of climate change on human comfort in outdoor urban environments. In the first step, climate change scenarios for air temperature and solar radiation (global, diffuse, direct components) are created using a change-factor algorithm. The change factors are calculated by comparing ranked daily regional climate model outputs for a future-period and a present-day period, and then changes consistent with these daily change factors are applied to historical hourly climate observations. In the second step, the mean-radiant-temperature (T mrt) is calculated using the SOLWEIG (SOlar and LongWave Environmental Irradiance Geometry) model. T mrt, which describes the radiant heat exchange between a person and their surroundings, is one of the most important meteorologically derived parameters governing human energy balance and outdoor thermal comfort, especially during warm and sunny days. We demonstrate that change factors can be applied independently to maximum air temperature and daily global solar radiation, and show that the outputs from the algorithm, when aggregated to daily values, are consistent with the driving regional climate model. Finally, we demonstrate how to obtain quantitative information from the scenarios regarding the potential impact of climate change on outdoor thermal comfort, by calculating changes in the distribution of hourly summer day-time T mrt and changes in the number of hours with T mrt >55 °C.

Mean radiant temperature (Tmrt) has shown to be an important meteorological variable in studies of human comfort and health. The Tmrt is defined as the ‘uniform temperature of an imaginary enclosure in which the radiant heat transfer from the human body equals the radiant heat transfer in the actual non-uniform enclosure’ (ASHRAE, 2001). One way to obtain Tmrt is to calculate the surface temperature of a standing man approximated as a cylinder emitting the same amount of longwave radiation as all shortand longwave radiation fluxes received from the surrounding four cardinal points and downand upwards. Fig. 1 shows an example of the equipment that can be used. The calculation was introduced by Höppe in (1992) and has then been used both in models (e.g. SOLWEIG) (Lindberg, Holmer, & Thorsson, 2008) and field studies (Kantor, Kovacs, & Lin, 2014; Kantor, Lin, & Matzarakis, 2014; Thorsson, Lindberg, Eliasson, & Holmer, 2007). However, the formula by Höppe describes in fact a man shaped like a box and not a cylinder as noted by Kantor, Lin, et al. (2014). The box shape has resulted in some peculiar features noticed in studies of Tmrt such as a local minimum at noon (e.g. Kantor, Kovacs, et al. (2014); Kantor, Lin, et al. (2014); Mayer, Holst, and Imbery (2009); Thorsson et al. (2007)) and an influence of the orientation of the field equipment (Kantor, Lin, et al., 2014).These anomalies occur not only in Tmrt calculated from field data but also in model calculations based on the Höppe formula, e.g. SOLWEIG. Thus the anomalies are caused by the calculation method and not connected to shortcomings of the equipment.

Grupphandledning av examensarbete inom geografi, med fokus på naturgeografi, vid Göteborgs Universitet infördes 2012 som ett komplement till den individuella handledningen i syfte att öka genomströmningen av studenter samt kvaliteten på arbetena. I denna artikel presenteras och utvärderas det aktuella kursupplägget. Såväl genomströmningen som kvaliteten (bearbetning och tolkning av materialet, teorianknytning, disposition och språk) ökade efter införandet av grupphandledning, vilket i linje med tidigare studier visar att grupphandledning är ett bra komplement till den traditionella individuella handledningen.

The authors analysed rainfall variability at Combolcha and Hayk in Ethiopia during the short rainy season, the Belg (February-May), in the period 1964-1996 and compared the results with similar data for the period 1997-2012. These towns are located 30 km apart in South Wollo. They have similar in topography and surrounding land use but differ in the amount of rainfall they receive. Daily rainfall data from local weather stations were used as input in a rainfall model for the cultivation of teff to analyse the number of years when it a harvest was possible. After 1996, Belg rainfall declined by 25-30% at both sites. The decline was greatest in February; Combolcha received one-third of its earlier rainfall. The teff model showed that the sowing date changed from February to March in both study areas. Between 1964 and 1996, lack of rain reduced the years with a harvest to every second year in Hayk and every third year in Combolcha. In the period 1997-2012, the number of years with a harvest was slightly reduced in Hayk, whereas in Combolcha it declined to one in every five years. Thus, both sites suffered from the diminished Belg rainfall but the consequences were worse for Combolcha.

Trees can mitigate heat stress in urban areas through shade and evapotranspiration (Mayer et al. 2009; Bowler et al. 2010; Shashua-Bar et al. 2011). However, in order to provide a cooling effect, urban trees need to remain healthy in spite of harsh growing conditions and stress factors absent or less severe in their natural environment (Roberts 1977). While transpiration of forest trees has been widely studied, little research has been conducted on the transpirational cooling effect of mature urban trees. Within the urban environment, trees growing over paved surfaces were found to have restricted growth and reduced gas exchange in comparison to those surrounded by grass or bare soil (Celestian and Martin 2005; Ferrini and Baietto 2007). Knowledge about the transpiration rates of urban trees and how these depend on environmental factors is essential for estimating the cooling effect provided by urban greenery as well as for appropriate urban planning and management to promote this ecosystem service. Transpiration in darkness is often assumed to be negligible due to stomatal closure. However, several studies have reported non-negligible night-time stomatal conductance and transpiration of trees in forests and urban parks (Snyder et al. 2003; Fisher et al. 2007; Chen et al. 2011), with an average of 5-15% of the daytime values, as reported in a review by Caird et al. (2007). While not directly measured, evening evapotranspiration has also been suggested by Lindén (2011) and Holmer et al. (2013) as a reason behind intensive nocturnal cooling of densely vegetated areas in the tropical city of Ouagadougou, Burkina Faso. The rapid cooling of vegetated areas in Ouagadougou around sunset, in the so called Phase 1 of nocturnal cooling (Holmer et al. 2007), was accompanied by an increase of specific humidity not observed at non-vegetated sites, which cooled more slowly. In Phase 2, starting around 2-3 h after sunset, the cooling was less intensive, with small differences in cooling between vegetated and non-vegetated sites. Nocturnal cooling rates are of high importance in urban climate studies, as an enhanced cooling in Phase 1 can lead to lower night-time air temperature, providing a relief from heat during heat waves and decreasing heat related mortality in urban areas (Rocklöv et al. 2011). The aims of this study are to: i) quantify the magnitude and diurnal variations of transpiration of the most common urban tree species in Gothenburg, Sweden, ii) analyse the influence of meteorological conditions and surface permeability on the transpiration of urban trees and iii) find out whether transpiration of urban trees contributes to daytime or nocturnal cooling.