Are detailed urban canopy parameters necessary for modelling the urban climate in Africa?

2020 ◽  
Author(s):  
Oscar Brousse ◽  
Jonas Van de Walle ◽  
Lien Arnalsteen ◽  
Matthias Demuzere ◽  
Wim Thiery ◽  
...  
Keyword(s):  
Climate Model ◽  
Urban Climate ◽  
Urban Canopy ◽  
Sub Saharan Africa ◽  
Climate Modelling ◽  
Local Climate ◽  
African Cities ◽  
Local Climate Zones ◽  
The City

<p>Local Climate Zones (LCZ) have now been widely accepted and used by the urban climate community (Ching et al., 2018). However, their use over Sub-Saharan Africa has still been limited because of data scarcity in the region. Brousse et al. (2019, 2020) demonstrated the added value of applying spatially variant urban canyon parameters derived from LCZ in the urban climate model TERRA_URB – embedded in the COSMO-CLM model. Despite its promising results, thermal and morphological parameters extracted out of the ranges proposed by Stewart and Oke (2012) are mostly derived from Western cities. Hence, uncertainties related to the use of unascertained urban forms and functions of African cities for urban climate modelling have not yet been evaluated.</p><p>To quantify the sensitivity of the model to more representative urban canopy parameters of African cities, this study sets up a methodology for: (i) obtaining from in situ measurements archetypal parameters of LCZ classes for Kampala (Uganda); and (ii) simulating the potential effect of the newly defined urban structure on the local climate.</p><p>In situ data were obtained during field work held in the summer months of 2018. A representative sample of 1300 measurement points was selected throughout the city of Kampala, for which both quantitative (road width, distance between houses, heights of buildings) and qualitatively estimated (vegetation fraction, road-wall-roof material) variables were collected.  These variables enabled the development of an updated LCZ map of the city of Kampala.</p><p>To evaluate the model’s sensitivity to the new spatially explicit urban morphological and thermal parameters, this new information was fed into the TERRA_URB scheme at a horizontal resolution of 1 km for a 3-months period (December 2017 – February 2018). The run was nested within a 12 km simulation forced by ERA-Interim reanalysis data. Results show tangible effects of the updated parameters on the 2-meter air temperature, land surface temperature and surface energy balance components. Still, no major improvements in model skill compared to the default LCZ framework proposed by Brousse et al. (2020) were found. [1] [WT2] This study is among the first studies to test the sensitivity of an urban climate model to more realistic urban parameters in Africa and aims at triggering more research to be done in the area with a variety of urban climate models.</p>

scholarly journals Impact of Urban Canopy Parameters on a Megacity’s Modelled Thermal Environment

Atmosphere ◽  
2020 ◽  
Vol 11 (12) ◽  
pp. 1349
Author(s):  
Mikhail Varentsov ◽  
Timofey Samsonov ◽  
Matthias Demuzere
Keyword(s):  
Urban Areas ◽  
Climate Model ◽  
Thermal Environment ◽  
Weather Prediction ◽  
Urban Canopy ◽  
Anthropogenic Heat ◽  
Climate Modelling ◽  
Local Climate ◽  
Anthropogenic Heat Flux ◽  
Local Climate Zones

Urban canopy parameters (UCPs) are essential in order to accurately model the complex interplay between urban areas and their environment. This study compares three different approaches to define the UCPs for Moscow (Russia), using the COSMO numerical weather prediction and climate model coupled to TERRA_URB urban parameterization. In addition to the default urban description based on the global datasets and hard-coded constants (1), we present a protocol to define the required UCPs based on Local Climate Zones (LCZs) (2) and further compare it with a reference UCP dataset, assembled from OpenStreetMap data, recent global land cover data and other satellite imagery (3). The test simulations are conducted for contrasting summer and winter conditions and are evaluated against a dense network of in-situ observations. For the summer period, advanced approaches (2) and (3) show almost similar performance and provide noticeable improvements with respect to default urban description (1). Additional improvements are obtained when using spatially varying urban thermal parameters instead of the hard-coded constants. The LCZ-based approach worsens model performance for winter however, due to the underestimation of the anthropogenic heat flux (AHF). These results confirm the potential of LCZs in providing internationally consistent urban data for weather and climate modelling applications, as well as supplementing more comprehensive approaches. Yet our results also underline the continued need to improve the description of built-up and impervious areas and the AHF in urban parameterizations.

Modelling the impact of a Sub-Saharan metropolis (Kampala) on the local climate during specific meteorological conditions of a dry season

2021 ◽  
Author(s):  
Oscar Brousse ◽  
Jonas Van de Walle ◽  
Matthias Demuzere ◽  
Alberto Martilli ◽  
Nicole van Lipzig ◽  
...  
Keyword(s):  
Urban Canopy ◽  
Building Energy ◽  
Dry Season ◽  
Meteorological Conditions ◽  
Sub Saharan Africa ◽  
Wave Radiation ◽  
Local Climate ◽  
Local Climate Zones ◽  
Sub Saharan ◽  
The Impact

<p>In order to build resilient cities in face of climate change in Sub-Saharan Africa, much is to be done to understand the impact of rapid and uncontrolled urbanization on the local climate in the region. Recent efforts by Brousse et al. (2019, 2020) demonstrated that using generic urban parameter information  derived out of Local Climate Zones (LCZ ; Stewart and Oke, 2012) maps created through the World Urban Database and Access Portal Tool framework (Ching et al. 2018) may be used to model the impact of Sub-Saharan African cities on their local climate – using the case of Kampala, the capital city of Uganda. These studies showed that despite the characteristic data scarcity on urban typologies that is present in Sub-Saharan Africa, LCZ could be used as a solution for modelling and studying the urban climates in the region.</p><p>Yet these conclusions were only obtained through the use of the bulk-level urban canopy model TERRA_URB, embedded in the COSMO-CLM regional climate model. We therefore test the applicability of a more complex urban canopy models – the Building Effect Parameterization coupled to the Building Energy Model (BEP-BEM) – over the region. To do so, we focus on short periods with specific meteorological conditions during the dry season spanning from December 2017 to February 2018. These are obtained through a k-means clustering over hourly weather measurements given by the automatic weather station located at the Makerere University, in the city-center of Kampala. Wind direction and speed, 2-meter air temperature, incoming short-wave radiation, precipitation, daily temperature range, 2-meter air relative humidity and near-surface pressure are used to depict 5 weather typologies (ie. clusters) during the dry season. We chose to keep only periods with 5 consecutive days of one weather typology, which results in three 5-day periods of distinct typology. We then run the model for these periods and evaluate its outputs against the state-of-the-art simulation by Brousse et al. (2020) as well as in-situ and satellite observations for certain meteorological variables. After that, we show the effect of the recent urbanization on the local climate for each of those three periods and relate it to the variability in urban heat.</p><p>This study is the first to model a tropical African city at 1 km horizontal resolution using the BEP-BEM model embedded in WRF. The latter could have major implications as more complex urban canopy models coupled to building energy models could shed light on the impact of the built environment on the livability of indoor and outdoor environments in these cities. Furthermore, insights could indeed be gained on the contribution of air conditioning heat fluxes to outdoor temperatures and the energetic consumption needed to keep indoor environments at an optimal temperature. Additionally, by resolving the urban environment in three dimensions, BEP-BEM could help increase our understanding of how specific urban planning and architectural adaptation strategies (like green or cool roofs, roof top solar panel, new building materials, urban greening etc.) may increase the citizens’ thermal comfort and reduce negative health impacts under specific weather conditions.</p>

Comparison of urban climate measurements in Berlin and LES model output for a special observation period

2021 ◽  
Author(s):  
Ines langer ◽  
Alexander Pasternack ◽  
Uwe Ulbrich ◽  
Henning Rust
Keyword(s):  
Mean Square Error ◽  
Urban Climate ◽  
Specific Humidity ◽  
Mean Square ◽  
Climate Zones ◽  
Local Climate ◽  
Large Eddy Simulation Model ◽  
Local Climate Zones ◽  
The City ◽  
Observation Period

<p>Surface (2 m) temperature and specific humidity data are measured at 5-minute intervals in a network comprising 33 stations distributed across the city of Berlin, Germany. These data are utilized in order to validate a LES (large eddy simulation) model designed to assess the local climate at a very high resolution of 10 m to 1 m. This model, was developed at the ​Institute of Meteorology and Climatology (IMUK) of the Leibniz Universität Hannover, Germany, and is developed into an application tool for city planners within the funding programme "[UC²] - Urban Climate under Change", of the German Federal Ministry of Education and Research (BMBF).</p><p>The evaluation distinguishes between the different Local climate zones (LCZ) in the city, which are defined following the concept of Stewart & Oke (2012). For Berlin, the following LCZ have been identified: 2 (compact midrise), 4 (open high-rise), 6 (open low-rise), 8 (large low-rise), A (dense trees), B (scattered trees), D (low Plants), G (water).</p><p>We analyzed one cold winter day during an intensive observation period from 06 UTC on 17<sup>th</sup> January to 06 UTC on 18<sup>th</sup> January, 2017. The minimum and maximum recorded temperatures were -8.1 °C and +2 °C, respectively, the sun shine duration was 6.5 hours. Daily and hourly mean absolute error, mean square error and root mean square error confirm that the deviation between measurements and the PALM-4U model differs between the LCZ for Berlin, with particularly large negative deviations of up to 5 K in forest areas, as they are not yet well represented in the model. Smallest deviations are found for the industrial zone. In all cases, the observed amplitude of the diurnal cycle is underestimated. The role of the driving model for the deviations found is addressed.</p><p>Stewart, I.D., Oke, T.R. (2012) Local climate zones for urban temperature studies. Bull. Amer. Meteor. Soc. 93 1879-1900. DOI: 10.1175/BAMS-D-11-00019.1.</p><p> </p>

scholarly journals Can local fieldwork help to represent intra-urban variability of canopy parameters relevant for tropical African climate studies?

2021 ◽  
Author(s):  
Jonas Van de Walle ◽  
Oscar Brousse ◽  
Lien Arnalsteen ◽  
Disan Byarugaba ◽  
Daniel S. Ddumba ◽  
...  
Keyword(s):  
Building Materials ◽  
Climate Model ◽  
Urban Climate ◽  
Boreal Summer ◽  
Future Research ◽  
Site Specific ◽  
Local Climate ◽  
African Cities ◽  
Climate Studies ◽  
Urban Characteristics

AbstractRapid and uncontrolled urbanization in tropical Africa is increasingly leading to unprecedented socio-economical and environmental challenges in cities, particularly urban heat and climate change. The latter calls for a better representation of tropical African cities’ properties relevant for urban climate studies. Here, we demonstrate the possibility of collecting urban canopy parameters during a field campaign in the boreal summer months of 2018 for deriving a Local Climate Zone (LCZ) map and for improving the physical representation of climate-relevant urban morphological, thermal and radiative characteristics. The comparison of the resulting field-derived LCZ map with an existing map obtained from the World Urban Data and Access Portal Tool framework shows large differences. In particular, our map results in more vegetated open low-rise classes. In addition, site-specific fieldwork-derived urban characteristics are compared against the LCZ universal parameters. The latter shows that our fieldwork adds important information to the universal parameters by more specifically considering the presence of corrugated metal in the city of Kampala. This material is a typical roofing material found in densely built environments and informal settlements. It leads to lower thermal emissivity but higher thermal conductivity and capacity of buildings. To illustrate the importance of site-specific urban parameters, the newly derived site-specific urban characteristics are used as input fields to an urban parametrization scheme embedded in the regional climate model COSMO-CLM. This implementations decreases the surface temperature bias from 5.34 to 3.97 K. Based on our results, we recommend future research on tropical African cities to focus on a detailed representation of cities, with particular attention to impervious surface fraction and building materials.

scholarly journals Data for the geoecology of solution karst dolines, with particular attention to climatic, soil and biogenic environment

2021 ◽  
Vol 55 (4) ◽  
pp. 27-71
Author(s):  
Ilona Bárány Kevei ◽  
Zoltán Zboray ◽  
Márton Kiss
Keyword(s):  
21St Century ◽  
Heat Load ◽  
Climate Model ◽  
Model Simulation ◽  
Urban Climate ◽  
Climate Index ◽  
Local Climate ◽  
Tropical Night ◽  
Mitigation And Adaptation ◽  
Local Climate Zones

In this study the changes in the nighttime heat load in Carpathian Basin cities during the 21st century were examined. To quantify the heat load, the tropical night climate index was used. The MUKLIMO_3 local scale climate model was used to describe the urban processes and the land use classes were defined by the local climate zones. The expected change was examined over three periods: the 1981–2010 was taken as reference period using the Carpatclim database and the 2021–2050 and 2071–2100 future periods using EURO-CORDEX regional model simulation data for two scenarios (RCP4.5 and RCP8.5). To combine the detailed spatial resolution and the long time series, a downscaling method was applied. Our results show that spectacular changes could be in the number of tropical nights during the 21st century and the increasing effect of the urban landform is obvious. In the near future, a slight increase can be expected in the number of tropical nights, which magnitude varies from city to city and there is no major difference between the scenarios. However, at the end of the century the results of the two scenarios differ: the values can be 15-25 nights in case of RCP4.5 and 30-50 nights in case of RCP8.5. The results show that dwellers could be exposed to high heat load in the future, as the combined effect of climate change and urban climate, thus developing various mitigation and adaptation strategies is crucial.

scholarly journals COSMO-BEP-Tree v1.0: a coupled urban climate model with explicit representation of street trees

2020 ◽  
Vol 13 (3) ◽  
pp. 1685-1710 ◽  
Author(s):  
Gianluca Mussetti ◽  
Dominik Brunner ◽  
Stephan Henne ◽  
Jonas Allegrini ◽  
E. Scott Krayenhoff ◽  
...  
Keyword(s):  
Air Temperature ◽  
Climate Model ◽  
Urban Climate ◽  
Coupled Model ◽  
Urban Canopy ◽  
Small Scale ◽  
Climate Modelling ◽  
Street Trees ◽  
Effective Measure ◽  
Weather And Climate

Abstract. Street trees are more and more regarded as an effective measure to reduce excessive heat in urban areas. However, the vast majority of mesoscale urban climate models do not represent street trees in an explicit manner and, for example, do not take the important effect of shading by trees into account. In addition, urban canopy models that take interactions of trees and urban fabrics directly into account are usually limited to the street or neighbourhood scale and hence cannot be used to analyse the citywide effect of urban greening. In order to represent the interactions between street trees, urban elements and the atmosphere in realistic regional weather and climate simulations, we coupled the Building Effect Parameterisation with Trees (BEP-Tree) vegetated urban canopy model and the Consortium for Small-scale Modeling (COSMO) mesoscale weather and climate model. The performance and applicability of the coupled model, named COSMO-BEP-Tree, are demonstrated over the urban area of Basel, Switzerland, during the heatwave event of June–July 2015. Overall, the model compared well with measurements of individual components of the surface energy balance and with air and surface temperatures obtained from a flux tower, surface stations and satellites. Deficiencies were identified for nighttime air temperature and humidity, which can mainly be traced back to limitations in the simulation of the nighttime stable boundary layer in COSMO. The representation of street trees in the coupled model generally improved the agreement with observations. Street trees produced large changes in simulated sensible and latent heat flux, and wind speed. Within the canopy layer, the presence of street trees resulted in a slight reduction in daytime air temperature and a very minor increase in nighttime air temperature. The model was found to realistically respond to changes in the parameters defining the street trees: leaf area density and stomatal conductance. Overall, COSMO-BEP-Tree demonstrated the potential of (a) enabling city-wide studies on the cooling potential of street trees and (b) further enhancing the modelling capabilities and performance in urban climate modelling studies.

scholarly journals Investigating the effect of land-use change on the heat load within two Austrian cities

2021 ◽  
Author(s):  
Robert Goler ◽  
Maja Žuvela-Aloise ◽  
Sandro Oswald ◽  
Brigitta Holllósi ◽  
Claudia Hahn ◽  
...  
Keyword(s):  
Land Use ◽  
Land Cover ◽  
Heat Load ◽  
Climate Model ◽  
Land Use Changes ◽  
Urban Climate ◽  
Climate Indices ◽  
Local Climate ◽  
Use Categories

<p>As the majority of the population live in cities, it is important to understand the urban climate and how it can change in the future. Accordingly, the ACRP-funded project LUCRETIA investigates how land use and land cover determine local climate characteristics within cities in Austria. </p><p>Historical land use data has been obtained for Graz and Vienna for a number of years and used as input into the microscale urban climate model MUKLIMO_3 to simulate both cities in conditions representing a typical summer day. In conjunction with the cuboid method, climate indices such as the average number of summer and hot days per year have been calculated to establish how the heat load changes from one year to another. Differences in the heat load have been related to changes in the land use focusing on (i) the change that occurs in situ and (ii) the change that occurs in the neighbourhood. <br> <br>It is shown that land use categories can be ordered according to their heat load, with categories containing larger amounts of greenery generally having lower heat loads. With the land use categories sorted in such a way, it enables a relatively quick assessment to be made of the effect of replacing one land use category with another, without having to employ expensive modelling tools. Furthermore, it is shown that land-use changes not only affect the heat load of the changed area in situ, but also the neighbourhood around where the change was made. This demonstrates that land-use changes may have a broader spatial impact than initially anticipated. The results from this study can serve as guidance for city planners regarding future land use and land cover changes.</p>

scholarly journals COSMO-BEP-Tree v1.0: a coupled urban climate model with explicit representation of street trees

2019 ◽  
Author(s):  
Gianluca Mussetti ◽  
Dominik Brunner ◽  
Stephan Henne ◽  
Jonas Allegrini ◽  
E. Scott Krayenhoff ◽  
...  
Keyword(s):  
Air Temperature ◽  
Climate Model ◽  
Urban Climate ◽  
Coupled Model ◽  
Urban Canopy ◽  
Climate Modelling ◽  
Street Trees ◽  
Night Time ◽  
Effective Measure ◽  
Weather And Climate

Abstract. Street trees are more and more regarded as an effective measure to reduce excessive heat in urban areas. However, the vast majority of mesoscale urban climate models do not represent street trees in an explicit manner and for example do not take the important effect of shading by trees into account. In addition, urban canopy models that take interactions of trees and urban fabrics directly into account are usually limited to the street or neighbourhood scale and, hence, cannot be used to analyse the citywide effect of urban greening. In order to represent the interactions between street trees, urban elements and the atmosphere in realistic regional weather and climate simulations, we coupled the vegetated urban canopy model BEP-Tree and the mesoscale weather and climate model COSMO. The performance and applicability of the coupled model, named COSMO-BEP-Tree, are demonstrated over the urban area of Basel, Switzerland, during the heatwave event of June–July 2015. Overall, the model compared well with measurements of individual components of the surface energy balance and with air and surface temperatures obtained from a flux tower, surface stations and satellites. Deficiencies were identified for night-time air temperature and humidity, which can mainly be traced back to limitations in the simulation of the night-time stable boundary layer in COSMO. The representation of street trees in the coupled model generally improved the agreement with observations. Street trees produced large changes in simulated sensible and latent heat flux, and wind speed. Within the canopy layer, the presence of street trees resulted in a slight reduction in daytime air temperature and a very minor increase in night-time air temperature. The model was found to realistically respond to changes in the parameters defining the street trees: leaf area density and stomatal conductance. Overall, COSMO-BEP-Tree demonstrated the potential of (a) enabling city-wide studies on the cooling potential of street trees and (b) further enhancing the modelling capabilities and performance in urban climate modelling studies.

scholarly journals Urban Cold and Heat Island in the City of Bragança (Portugal)

Climate ◽  
2018 ◽  
Vol 6 (3) ◽  
pp. 70 ◽  
Author(s):  
Artur Gonçalves ◽  
Gabriella Ornellas ◽  
António Castro Ribeiro ◽  
Filipe Maia ◽  
Alfredo Rocha ◽  
...  
Keyword(s):  
Rural Areas ◽  
Urban Areas ◽  
Thermal Environment ◽  
Urban Climate ◽  
Heat Island ◽  
Local Climate ◽  
Climate Conditions ◽  
Urban Green Spaces ◽  
Local Climate Zones ◽  
The City

The thermal environment is an important aspect of the urban environment because it affects the quality of life of urban residents and the energy use in buildings. Urban Heat Island (UHI) and Urban Cold Island (UCI) are complementary effects that are the consequence of cities’ structures interference with the local climate. This article presents results from five years of urban climate monitoring (2012–2016) in a small Portuguese city (Bragança) using a dense meteorological network of 23 locations covering a wide array of Local Climate Zones (LCZ), from urban areas to nearby rural areas. Results show the presence of both the UHI effect, from mid-afternoon until sunrise, and the UCI after sunrise, both being more intense under the dense midrise urban context and during the summer. Urban Green Spaces had an impact on both UHI and UCI, with an important role in cooling areas of the city during daytime in the summer. Other LCZs had less impact on local thermal conditions. Despite the small size of this city, both effects (UHI and UCI) had a relevant intensity with an impact on local climate conditions. Both effects tend to decrease in intensity with increasing wind speed and precipitation.

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