Importance of radiative transfer processes in urban climate models: a study based on the PALM 6.0 model system

Including radiative transfer processes within the urban canopy layer into microscale urban climate models (UCMs) is essential to obtain realistic model results. These processes include the interaction of buildings and vegetation with shortwave and longwave radiation, thermal emission, and radiation reflections. They contribute differently to the radiation budget of urban surfaces. Each process requires different computational resources and physical data for the urban elements. This study investigates how much detail modellers should include to parameterize radiative transfer in microscale building-resolving UCMs. To that end, we introduce a stepwise parameterization method to the Parallelized Large-eddy Simulation Model (PALM) system 6.0 to quantify individually the effects of the main radiative transfer processes on the radiation budget and on the flow field. We quantify numerical simulations of both simple and realistic urban configurations to identify the major and the minor effects of radiative transfer processes on the radiation budget. The study shows that processes such as surface and vegetation interaction with shortwave and longwave radiation will have major effects, while a process such as multiple reflections will have minor effects. The study also shows that radiative transfer processes within the canopy layer implicitly affect the incoming radiation since the radiative transfer model is coupled to the radiation model. The flow field changes considerably in response to the radiative transfer processes included in the model. The study identified those processes which are essentially needed to assure acceptable quality of the flow field. These processes are receiving radiation from atmosphere based on the sky-view factors, interaction of urban vegetation with radiation, radiative transfer among urban surfaces, and considering at least single reflection of radiation. Omitting any of these processes may lead to high uncertainties in the model results.

Climate Integration in Sustainable Urban Planning

Currently, cities are home to more than half of the world's population. The increasing urbanization rates create an unprecedented urban sprawl that worsens the urban climate situation. Urban areas modify their local climate and face the consequent urban climate impacts, which are particularly exacerbated by global climate change. This chapter shares scientific knowledge on how cities affect their climate and how urban spatial planning can mitigate the negative impacts of urban climate. Focus is given on the urban heat island, the most documented aspect of urban climate, directly linked to city spatial characteristics and functions. This phenomenon is explained, and tools and methods to assess it and mitigate its intensity are introduced in an attempt to help urban planners and designers to use climatic knowledge in urban planning to build more sustainable and climate-resilient cities.

Clima urbano: episódios de inverno e primavera em Rio Verde-GO

A perda de áreas florestadas causa extremos climáticos, como picos de temperatura e quedas da umidade relativa do ar, comprometendo a qualidade ambiental. Em Rio Verde, Goiás, com a expansão da área urbana, áreas de floresta foram reduzidas, trazendo um desconforto térmico na população. Assim, o objetivo deste artigo foi estimar as variações de temperatura e umidade relativa do ar, em três pontos de coletas distintos na cidade de Rio Verde-GO, considerando-se as características da superfície (uso da terra, vegetação, relevo) durante os meses de julho (inverno) e outubro (primavera) de 2018. Para isso foram processadas relações entre as temperaturas (T) e umidade relativa (UR) do ar com as áreas (vegetada; construída/pavimento e solo exposto) num raio de 200 m entre os pontos de coletas. Com essas informações fundamentadas no estudo na Teoria do Clima Urbano, por meio do subsistema termodinâmico (relativo à temperatura e umidade relativa do ar) foram feitas relações estatísticas entre a variação dos atributos climáticos e observamos os parâmetros geográficos, tais como porcentagem de vegetação, área construída, solo exposto, e a atuação e dinâmica atmosférica da região no período analisado. Os resultados mostraram que os aspectos do meio físico dos pontos amostrais, principalmente a vegetação, contribuiu para a variação dos registros da temperatura do ar mínima (T. mín) e máxima (T. máx) absoluta , com oscilação de 1,4 a 2,5°C e 2,8 a 4°C, enquanto os valores da umidade relativa do ar mínima e máxima absoluta variaram de 0,6 a 11,6% e 2,2 a 5,4%, respectivamente.Urban climate: winter and spring episodes in Rio Verde-GOA B S T R A C TThe loss of forested areas causes climatic extremes, such as temperature peaks and drops in relative humidity, compromising environmental quality. In Rio Verde, Goiás, with the population growth and the expansion of the urban area, forest areas were decimated, bringing a thermal discomfort to the population. The objective of this article was to estimate the variations in temperature and relative humidity in three distinct collection points in the city of Rio Verde-GO, considering the surface characteristics (land use, vegetation, relief) during the months of July (winter) and October (spring) 2018. For this purpose, relationships between the temperatures (T) and relative humidity (RH) of the air were processed with the areas (vegetated; constructed/paved and exposed soil) within a radius of 200 m between the collection points. With this information based on the study in the Theory of Urban Climate, through the thermodynamic subsystem (relative to the temperature and relative humidity of the air), statistical relationships were made between the variation of climatic attributes and we observed the geographical parameters, such as percentage of vegetation, area constructed, exposed soil, and the performance and atmospheric dynamics of the region in the analyzed period. The results showed that the physical aspects of the sample points, mainly the vegetation, contributed to the variation of the minimum (T. min) and maximum (T. max) absolute air temperature records, with an oscillation of 1,4 to 2,5°C and 2,8 to 4°C, while the minimum and maximum absolute relative humidity values varied from 0,6 to 11,6% and 2,2 to 5,4%, respectively.Keywords: Urban climate, climatic attributes, physical environment, land use and occupation

Véderdő telepítésének lehetséges jövőbeli hatásai Szeged hőterhelésében

n this study the possible future thermal consequences of a fictional protective forest around Szeged were examined. The aims of this installation are the adaptation to climate change and reducing air pollution. However, the complex effects of local urban climate should be taken into consideration as well. Therefore, the changing of heat load due to the forest was studied by presenting the change of climate indices during the 21st century. In order to simulate the local circumstances of the city, a MUKLIMO_3 local scale model was applied. EURO-CORDEX regional model simulations ensured the climate data for periods 2021–2050 and 2071–2100 using scenarios RCP4.5 and RCP8.5. Our results show that the effect of the protective forest is not favourable in certain parts of the city due to the reduction or block of the ventilation. The forest induces cooling effect mostly during daytime, but the extent of unfavourable effects exceeds the advantages especially at night time.

Using the dendro-climatological signal of urban trees as a measure of urbanization and urban heat island

Using dendroclimatological techniques this study investigates whether inner city tree-ring width (TRW) chronologies from eight tree species (ash, beech, fir, larch, lime, sessile and pedunculate oak, and pine) are suitable to examine the urban heat island of Berlin, Germany. Climate-growth relationships were analyzed for 18 sites along a gradient of increasing urbanization covering Berlin and surrounding rural areas. As a proxy for defining urban heat island intensities at each site, we applied urbanization parameters such as building fraction, impervious surfaces, and green areas. The response of TRW to monthly and seasonal air temperature, precipitation, aridity, and daily air-temperature ranges were used to identify climate-growth relationships. Trees from urban sites were found to be more sensitive to climate compared to trees in the surrounding hinterland. Ring width of the deciduous species, especially ash, beech, and oak, showed a high sensitivity to summer heat and drought at urban locations (summer signal), whereas conifer species were found suitable for the analysis of the urban heat island in late winter and early spring (winter signal).The summer and winter signals were strongest in tree-ring chronologies when the urban heat island intensities were based on an area of about 200 m to 3000 m centered over the tree locations, and thus reflect the urban climate at the scale of city quarters. For the summer signal, the sensitivity of deciduous tree species to climate increased with urbanity.These results indicate that urban trees can be used for climate response analyses and open new pathways to trace the evolution of urban climate change and more specifically the urban heat island, both in time and space.

Barriers and Enablers for Integrating Public Health Cobenefits in Urban Climate Policy

Urban climate policy offers a significant opportunity to promote improved public health. The evidence around climate and health cobenefits is growing but has yet to translate into widespread integrated policies. This article presents two systematic reviews: first, looking at quantified cobenefits of urban climate policies, where transportation, land use, and buildings emerge as the most studied sectors; and second, looking at review papers exploring the barriers and enablers to integrating these health cobenefits into urban policies. The latter reveals wide agreement concerning the need to improve the evidence base for cobenefits and consensus about the need for greater political will and leadership on this issue. Systems thinking may offer a way forward to help embrace complexity and integrate health cobenefits into decision making. Knowledge coproduction to bring stakeholders together and advance policy-relevant research for urban health will also be required. Action is needed to bring these two important policy agendas together. Expected final online publication date for the Annual Review of Public Health, Volume 43 is April 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Estimating Terrestrial Radiation for Human Thermal Comfort in Outdoor Urban Space

Cities inadvertently create warmer and drier urban climate conditions than their surrounding areas through urbanization that replaces natural surfaces with impervious materials. These changes cause heat-related health problems and many studies suggest microclimatic urban design (MUD) as an approach to address these problems. In MUD-related research, although terrestrial radiation plays an important role in human thermal comfort and previous studies use thermal comfort models to identify human heat stress, few studies have addressed the effect of terrestrial radiation. This study develops the ground ratio factor (GRF) model to estimate the different terrestrial radiation according to different ground conditions. Three types of ground materials (asphalt, concrete, and grass) were considered in the model, and field studies were conducted in humid subtropical climate (Cfa) zone during the hot season (13 July to 19 September 2020). The model was validated by comparing the predicated terrestrial radiation (PTR) from the model with the actual terrestrial radiation (ATR). The results showed that there is a statistically significant strong correlation between PTR and ATR. The model can contribute to MUD strategies by updating existing human energy budget models, which can lead to the measurement of more accurate human thermal comfort for mitigating thermal environments.