Aim: Climatic conditions exert a strong control on the geographic distribution of many woodland-to-grassland transition zones (or 'tree lines'). Because woody plants have, in general, a weaker cold ...tolerance than herbaceous vegetation, their altitudinal or latitudinal limits are strongly controlled by cold sensitivity. While temperature controls on the dynamics of woodland–grassland ecotones are relatively well established, the ability of woody plants to modify their microclimate and to create habitat for seedling establishment and growth may involve a variety of processes that are still not completely understood. Here we investigate feedbacks between vegetation and microclimatic conditions in the proximity to woodland–grassland ecotones. Location: We concentrate on arctic and alpine tree lines, the transition between mangrove forests and salt marshes in coastal ecosystems, and the shift from shrubland to grassland along temperature gradients in arid landscapes. Methods: We review the major abiotic and biotic mechanisms underlying the ability of woody plants to alter the nocturnal microclimate by increasing the temperatures they are exposed to. Results: We find that in many arctic, alpine, desert and coastal landscapes the presence of trees or shrubs causes nocturnal warming thereby favouring the establishment and survival of woody plants. Main conclusion: Because of this feedback, trees and shrubs may establish in areas that would be otherwise unsuitable for their survival. Thus, in grassland–woodland transition zones both vegetation covers may be (alternative) stable states of the landscape, thereby affecting the way tree lines may migrate in response to regional and global climate change.
•We examined micro-scale outdoor thermal comfort within a large tropical urban park.•4 Different park sites were assessed through climate measurements and user surveys.•Significant differences ...existed between measured and perceived thermal comfort.•These differences are notable between park sites and between monsoon seasons.•Humidity and wind conditions are potentially critical for tropical thermal comfort.
Urban greenery is a favoured approach applied towards reducing urban warmth and climate discomfort, but ascertaining its measured and perceived effectiveness in tropical climates is relatively understudied. To this end, we investigated microclimate differences within an urban park (the Singapore Botanic Gardens) to assess if variations in plot-scale land cover affect both objective (measured) and subjective (surveyed) microclimate data. Over two monsoonal seasons, we obtained data from four distinct sites—a tropical rainforest stand, a palm tree valley, a water-body feature, and the park visitors’ centre. Measured climate data (e.g. air temperature, vapour pressure, wind velocity and globe temperatures) were used to derive mean radiant temperature Tmrt and three thermal comfort indices (e.g. temperature-humidity index THI, physiological equivalent temperature PET, and wet-bulb globe temperature WBGT). Concurrent to these measurements, we also surveyed park users (n=1573) for perceived microclimate sensations and preferences in thermal, humidity, wind and sun exposure, as well as their overall assessment of climate comfort/discomfort. The results indicate significant differences in both measured and perceived microclimates over different sites and seasons, with (i) selected heat stress thresholds based on thermal comfort indices exceeded at several sites, and (ii) visitors perceived generally hot, humid and low-wind conditions throughout. Variations in respondent acclimatisation to tropical climates are observed between correlations of WBGT and some sensation votes, with apparently stronger correlations with more acclimated respondents. While humidity was voted as the most uncomfortable climate variable across all sites, a large majority of respondents felt comfortable climate conditions throughout. Present results confirm that vegetation canopy characteristics affecting wind and sun exposure appear to be important factors in outdoor thermal comfort. Lastly, we suggest that future tropical outdoor thermal comfort studies consider the critical aspects of site humidity and wind to discern comfort/discomfort levels.
Woody plant encroachment into grasslands is a major land cover change taking place in many regions of the world, including arctic, alpine and desert ecosystems. This change in plant dominance is also ...affecting coastal ecosystems, including barrier islands, which are known for being vulnerable to the effects of climate change. In the last century, the woody plant species Morella cerifera L. (Myricaceae), has encroached into grass covered swales in many of the barrier islands of Virginia along the Atlantic seaboard. The abrupt shift to shrub cover in these islands could result from positive feedbacks with the physical environment, though the underlying mechanisms remain poorly understood. We use a combination of experimental and modeling approaches to investigate the role of climate warming and the ability of M. cerifera to mitigate its microclimate thereby leading to the emergence of alternative stable states in barrier island vegetation. Nighttime air temperatures were significantly higher in myrtle shrublands than grasslands, particularly in the winter season. The difference in the mean of the 5% and 10% lowest minimum temperatures between shrubland and grassland calculated from two independent datasets ranged from 1.3 to 2.4°C. The model results clearly show that a small increase in near-surface temperature can induce a non-linear shift in ecosystem state from a stable state with no shrubs to an alternative stable state dominated by M. cerifera. This modeling framework improves our understanding and prediction of barrier island vegetation stability and resilience under climate change, and highlights the existence of important nonlinearities and hystereses that limit the reversibility of this ongoing shift in vegetation dominance.
The demonstration of survival of forest stands in relatively stable refugia during cold glacial stages has offered an increased understanding of the response of vegetation to climate change, but also ...provides insight into considerations for the conversation of biodiversity hotspots. However, refugia studies in China remain in question due to the lack of plant macrofossils, especially those of endemic and relict species. Palynology, while more broad brush, provides a method for exploring whether refugia occur, and can provide some details of palaeovegetation composition and temporal dynamics. Here, three pollen records derived from subalpine wetlands in central China, spanning the Last Glacial Maximum (LGM), have been coupled with biome and mean annual precipitation (MAP) reconstructions to identify the presence of trees that endured cold climate. The results indicated that some forest, including temperate deciduous broadleaf forest and cool mixed forest, survived the LGM at the three locations, and was thus at odds with the hypothesis that forests were replaced by herbs and grasses in central China at that time. Refugia favored by protection from cold air drainage and the availability of adequate water can explain the survival of the trees during otherwise harsh episodes. Our findings are consistent with other records from central China that argue for tree dominated refugia during the LGM.
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•Biomization reconstructs the regional landscape from three fossil pollen records.•Mean annual precipitation meets the threshold required for forest survival.•Central China was home to glacial refugia during the LGM.•Geographical and climatic factors play important roles on survival of trees.
•This research estimated building energy changes due to UHII and urban vegetation.•The summer UHI alone increased the air conditioning load between 9% and 12%.•Adding 5% mature trees in the urban ...case reduced peak UHII by 1.0°C.•Energy modelling estimated a reduction of 2.7% in July chiller energy due to trees.•Energy savings increased to 4.8% under a three-day period of peak UHI conditions.
Climate change projections estimate a rise of approximately 3°C by the 2080s for most of the UK (medium emissions scenario at 50% probability level, 1961–1990 baseline). Warming is a particular concern for urban areas due to urban densification and the Urban Heat Island (UHI) effect.
To counteract the UHI, one adaptation strategy for urban areas is increasing the proportion of greenspace, such as parks, street tree plantings, and green roofs. This research employed an interdisciplinary approach to measure and model fine-scale microclimate changes due to greenspace and explore the implications for building energy demand in Manchester, UK. Both the modelled and measured microclimate data informed development of a series of weather files for building energy modelling of three commercial building types.
For a scenario adding 5% mature trees to the urban case study, the combination of microclimate modelling and data analysis estimated a maximum hourly air temperature reduction of nearly 1.0°C under peak UHI conditions and wind speed reductions up to 1.0m/s. These results were used to change the weather files in the building energy modelling, which estimated a reduction of 2.7% in July chiller energy due to the combination of reduced UHI peak hours and eight additional trees shading a three-storey shallow plan building. Energy savings increased to 4.8% under a three-day period of peak UHI conditions.
The article concerns the problematics of unburned earth used as material for moulding formwork or clay plaster with lowered contraction, especially about interior unburned earth plaster with the ...heightened percentage of clay and therefore improved sorption abilities. By adding a plasticizer, it is possible to modify the fluidity of the mixture. With lessening the amount of water it is possible to lower the shrinkage. Furthermore, we can increase the ratio of clay to sand and thus we can control the indoor microclimate. This is because the clay provides adsorption properties. Unburnt clay has been widely used as a building material in the past around the world. In the last century, this material was rather despised. Nowadays, however, this trend is reversing and the unburnt clay is experiencing a renaissance. Increasingly people emphasize ecology, a healthy and balanced indoor climate, and demand buildings with low operational and energy intensity. All this can be offered by unburnt clay, because it is energy-efficient in production, easily accessible in almost all parts of the world, harmless, and beneficial to human health, as clay can contribute to the improvement of the internal microclimate to a much greater extent than other building materials, as confirmed by many scientific findings.
Weather data is a key input to achieve reliable building energy simulation, and in current studies, EnergyPlus Weather (EPW) data, historically measured by a few suburban weather stations, is the ...most widely used. However, weather is shaped by urban morphology and other factors, so transforming weather files for the urban context using tools such as Urban Weather Generator becomes necessary. This study investigated the differences between multi-sourced weather datasets after transforming, and, in turn, the subsequent impact on urban building energy simulation. As a case study, one campus block was selected, with 41 urban blocks and their urban morphologies obtained. One microclimate station and 16 sensors were then installed to collect weather data to validate multi-sourced weather files for energy simulation models. The study results showed the root mean square error of temperature differences between suburban weather station, EPW and on-campus microclimate was 2.1 °C and 4.3 °C, respectively, before transforming and 1.2 °C and 4.1 °C, respectively, after transforming. Regarding building energy use, the mean absolute percentage difference (MAPD) of cooling-energy use intensity (EUI) between those calculated using the three datasets was 32.4% and 13.1%, respectively, before transforming and 25.8% and 4.1%, respectively, after transforming. Meanwhile, the MAPD of heating-EUI was 27.2% and 116.3%, respectively, before transforming and 12.7% and 93.6%, respectively, after transforming. This study results provide a reference for selecting weather data for urban building energy modelling to achieve a reliable energy decision-making process.
Life quality in urban contexts is related to several interconnected factors. Lots of innovative technologies allow for the gathering of real-time information, which is helpful for analysing and ...interpreting significant urban dynamics and citizens’ behaviours. The presence of people in outdoor environments, particularly for social and recreational purposes, can be considered as a qualitative indicator, giving evidence of a living environment. The relationship between urban areas and the climate context has been addressed in recent years by the scientific literature. However, these studies did not report the direct correlation between people’s presence and outdoor thermal comfort in outdoor spaces. The aim of this paper is to assess whether the presence of people in outdoor public spaces, detected through human presence sensors, can be associated with outdoor microclimatic conditions (both with on-site measurement and software simulation) and outdoor thermal comfort indicators (as physiological equivalent temperature). The question is whether there exists a direct correlation between outdoor microclimate in public spaces and people’s presence, and if a public event plays a role in changing it. The research compares on-site measurements of physics variables (e.g., air temperature) and people’s presence with outdoor microclimate maps by Envi-met. The case study, carried out in the framework of the H2020 project ROCK—Regeneration and Optimization of Cultural Heritage in Creative and Knowledge cities, focuses on two squares located in Bologna’s historic city center. The conclusions show that public events are the main deciding factor influencing square crowding; nevertheless, the study reveals a relationship between thermal comfort and the number of people.
•Microclimate data measured in different urban spaces (squares, parks, courtyards).•Data for surface, air and globe temperatures, humidity, wind speed, solar radiation.•Effects of ground surface ...materials, shading, vegetation, water.•High pavement albedo reduces surface temperatures and increases globe temperatures.•Tree shade has the largest influence on microclimate and pedestrian thermal comfort.
The microclimates of open spaces in cities are highly influenced by urban geometry and construction materials. The present study reports on measurements of microclimate data taken in different open urban spaces such as parks, squares and courtyards featuring various ground surface materials, in particular asphalt, concrete, marble, granite, porous stone, cobble stone, ceramic tiles, gravel, grass and water. The measured data were used to assess the effect of morphologic features and material properties on microclimate development. Measurements were taken in two stages, starting with exploratory readings followed by corrective and complementary measurements. These took place in six different sites in the city of Thessaloniki, in northern Greece. The measurements include surface and ambient temperatures, relative humidity and wind velocity readings. Spot measurements of direct and reflected solar radiation were also taken for an indicative calculation of surface albedo. The second round of measurements included globe temperatures in order to estimate the effect of the radiant environment on pedestrian thermal comfort. The results show differences between and within open spaces and their surfaces, thus highlighting the effects of shading, vegetation, water and material properties on microclimate development and pedestrian thermal comfort.
•Lake Urmia’s energy and water balance were investigated from 2001 to 2020.•The heat storage capacity of Lake Urmia exponentially varies with its area.•The declined cooling effect of Lake Urmia ...explains the rising maximum temperatures.•Lake Urmia’s depleted heat storage can exacerbate the impact of climate change.
The catastrophic drying of Lake Urmia, once the world’s second-largest saline lake, has led to the degradation of its vital ecosystem services, including microclimate regulation. This study investigates the variation of Lake Urmia’s heat storage, a key driver of its microclimate regulation function, from 2001 to 2020. We analyze Lake Urmia’s monthly energy and water balances considering the spatial variation of hydro-meteorological variables over the lake and explicitly accounting for lake salinity. We found that the heat storage capacity of Lake Urmia has exponentially depleted with its shrinkage. The NRMSE values of the proposed equations for Lake Urmia’s maximum and minimum heat storage were 0.24 and 0.20, respectively. As a potential consequence, the maximum air temperature over the lake has increased while the minimum temperature has remained constant. The reviled role of Lake Urmia’s heat storage capacity in hindering the maximum annual temperature of the area can provide valuable insights into the role of lake conservation in mitigating climate warming.
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