Highest Urban Heat Island Intensity Research Articles

Effects of urban planning indicators on urban heat island: a case study of pocket parks in high-rise high-density environment

Due to urbanization, the urban heat island (UHI) effect has become a modern endemic threat to human health and energy consumption, especially in compact urban areas with high population density. Pocket parks, as the major component of urban green space in high-rise high-density built area of Hong Kong, play important roles in shaping the city. By conducting in situ climate measurements and morphological analysis of 12 sites in Hong Kong, this study investigates the impact of pocket parks on UHI intensity, and the relationships between five urban planning indicators and UHI. Results show that pocket parks and their surrounding areas in Hong Kong have a moderate UHI intensity (0.1°C) during the daytime but a very high nighttime UHI intensity (2.39°C). Ten parks are cooler than their surrounding urban streets for both daytime and nighttime, which means that pocket parks in Hong Kong can help to alleviate UHI intensity at the micro scale. Floor Area Ratio (FAR), building density and Tree Cover Ratio (TCR) are found to be significantly and negatively related with daytime UHI. It indicates that higher FAR, building density and TCR in high-rise high-density urban environment may help to reduce daytime UHI intensity without increasing the early nighttime intensity. Planting trees is an effective measure to reduce the UHI intensity inside the parks for high-rise high-density urban environment. But a threshold for TCR (around 42%) shall be achieved to maximize its cooling effect.

Impacts of urban surface characteristics on spatiotemporal pattern of land surface temperature in Kunming of China

To explore impacts of urban surface characteristics on spatiotemporal pattern of land surface temperature (LST), LST was retrieved from the thermal infrared band of satellite images and five indices were selected and extracted from remote sensing images in different time periods respectively acquired from 1992 to 2014. The correlation analysis (pixel by pixel) and linear regression analysis showed that although Normalized Difference Built-up Index (NDBI) and LST had the highest correlation coefficient, a combination of Modified Normalized Difference Water Index (MNDWI) and Normalized Difference Vegetation Index (NDVI) yielded the best regression results (the mean of R-squared value increased 0.1). These results showed that both NDBI and NDVI-MNDWI would be acceptable indicators of LST, but NDVI-MNDWI could be better. Moreover, urban heat island (UHI) intensity (represented by LST) analysis showed that the highest UHI intensity appeared in the April, while the lowest UHI intensity index emerged in June. These results suggested that both UHI intensity and UHI intensity index might be closely related to land surface moisture. Furthermore, the regions of UHI intensity index greater than 0.5 were unchanged essentially from 2000 to 2014. So, these regions would be considered as key areas where the UHI could be focused on elimination.

The Impact of Morphological Features on Summer Temperature Variations on the Example of Two Residential Neighborhoods in Ljubljana, Slovenia

The study conducted in this paper is focused on a predominantly residential area of the City of Ljubljana—Koseze, which is characterized by generally favorable (bio)climatic conditions. Nonetheless, thermal satellite images showed that residential neighborhoods within the Koseze district display unexpected variations in summer temperatures. This observation called into question the benefits of existing bioclimatic features and indicated the need to investigate and compare two neighborhoods with similar urban parameters, with the aim to identify morphological differential characteristics impacting urban heat island (UHI) intensity. By applying the study methodology based on a literature review, surveys of key precedents, detailed mapping in two Koseze locations, in situ measurements, observations and recordings, thermal imagery, and the analyses of statistical data, as well as by defining the four main categories of morphological urban parameters—structure, cover, fabric and metabolism, it was concluded that both neighborhoods have common morphological elements mitigating the UHI effect. Additionally, it was found that the neighborhood with higher UHI intensity has several less favorable features, such as busier roads, larger surface of parking corridors, and the existence of underground parking space. The traffic as an element of urban morphology hence represents the main cause of differences among UHI levels in the two Koseze neighborhoods.

The influence of atmospheric circulation on the intensity of urban heat island and urban cold island in Pozna\u0144, Poland

The study has analyzed influence of an atmospheric circulation on urban heat island (UHI) and urban cold island (UCI) in Poznań. Analysis was conducted on the basis of temperature data from two measurement points situated in the city center and in the Ławica airport (reference station) and the data concerning the air circulation (Niedźwiedź’s calendar of circulation types and reanalysis of National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR)). The cases with UHI constitute about 85 % of all data, and UCI phenomena appear with a frequency of 14 % a year. The intensity of UHI phenomenon is higher in the anticyclonic circulation types. During the year in anticyclonic circulation, intensity of UHI is 1.2 °C on average while in cyclonic is only 0.8 °C. The occurring of UHI phenomena is possible throughout all seasons of the year in all hours of the day usually in anticyclonic circulation types. The cases with highest UHI intensity are related mostly to nighttime. The cases of UCI phenomena occurred almost ever on the daytime and the most frequently in colder part of the year together with cyclonic circulation. Study based on reanalysis data indicates that days with large intensity of UHI (above 4, 5, and 6 °C) are related to anticyclonic circulation. Anticyclonic circulation is also promoting the formation of the strongest UCI. Results based on both reanalysis and the atmospheric circulation data (Niedźwiedź’s circulation type) confirm that cases with the strongest UHI and UCI during the same day occur in strong high-pressure system with the center situated above Poland or central Europe.

WRF model evaluation for the urban heat island assessment under varying land use/land cover and reference site conditions

Urban heat island effect in Delhi has been assessed using Weather Research and Forecasting (WRF v3.5) coupled with urban canopy model (UCM) focusing on air temperature and surface skin temperature. The estimated heat island intensities for different land use/land cover (LULC) have been compared with those derived from in situ and satellite observations. The model performs reasonably well for urban heat island intensity (UHI) estimation and is able to reproduce trend of UHI for urban areas. There is a significant improvement in model performance with inclusion of UCM which results in reduction in root mean-squared errors (RMSE) for temperatures from 1.63 °C (2.89 °C) to 1.13 °C (2.75 °C) for urban (non-urban) areas. Modification of LULC also improves performance for non-urban areas. High UHI zones and top 3 hotspots are captured well by the model. The relevance of selecting a reference point at the periphery of the city away from populated and built-up areas for UHI estimation is examined in the context of rapidly growing cities where rural areas are transforming fast into built-up areas, and reference site may not be appropriate for future years. UHI estimated by WRF model (with and without UCM) with respect to reference rural site compares well with the UHI based on observed in situ data. An alternative methodology is explored using a green area with minimum temperature within the city as a reference site. This alternative methodology works well with observed UHIs and WRF-UCM-simulated UHIs but has poor performance for WRF-simulated UHIs. It is concluded that WRF model can be applied for UHI estimation with classical methodology based on rural reference site. In general, many times WRF model performs satisfactorily, though WRF-UCM always shows a better performance. Hence, inclusion of appropriate representation of urban canopies and land use–land cover is important for improving predictive capabilities of the mesoscale models.

Impacts of inland water area changes on the local climate of Wuhan, China

A distinct feature of Wuhan is that almost a quarter of the total area of this city is covered with water, leading to its unique hot and humid climate characteristics in summer. However, according to records, water area in built-up zone of Wuhan has been reduced by 130.5 km2 from 1965 to 2008, while the annual average air temperature has been increased by more than 3℃. To investigate the quantitative connection between the water area reduction and air temperature increase, three scenarios were simulated in a summer; to evaluate the impact of water reduction on the local thermal environment in different water areas; and to study the impact of water reduction on the urban heat island (UHI) phenomenon. Meso-scale meteorological models of Weather Research and Forecasting model were applied in this study for quantitative assessment and prediction. With the predictions, this study reveals that the decreased water area could affect air temperature, wind velocity and wind flow direction, energy balance and the UHI intensity. The simulations show that areas with significant wind velocity, wind direction and air temperature differences are distributed among the downwind zones. Moreover, the areas with high UHI intensity are wider and farther from the boundary of urban areas because of the reduction of water areas.

A numerical study of the Urban Heat Island over Madrid during the DESIREX (2008) campaign with WRF and an evaluation of simple mitigation strategies

AbstractNowadays, mesoscale meteorological models coupled to Urban Canopy Parameterizations (UCP) can be used to complement and interpret the information gathered from intensive meteorological campaigns on the behaviour of the Urban Boundary Layer (UBL). Moreover, the impact of the air conditioning (AC) systems on the air temperature, the relationships existing between energy consumption (EC) and meteorological conditions, and the evaluation of strategies to mitigate the Urban Heat Island (UHI) phenomenon can be evaluated using detailed UCP. In this work, a new UCP implemented in the Weather Research and Forecasting (WRF) model (version V3.2) has been tested over the city of Madrid using two different turbulent parameterisations of the Planetary Boundary Layer (PBL) under atmospheric conditions that were favourable for a large UHI. Two selected days were analysed coinciding with the Dual‐use European Security IR Experiment (DESIREX) campaign that took place in the summer of 2008, and focused on Urban Heat Island (UHI) and Urban Thermography (UT) monitoring and assessment. For the two simulated days (30 June and 1 July) a high UHI intensity (5‐6 °C) was observed and modelled. Numerical results for the surface air temperature and wind speed were compared against measurements showing a global satisfactory performance of the model. Some differences in the air temperature predictions were observed within the two turbulent schemes. Subsequently, the impact of the AC systems and the EC were evaluated for the simulated period. The heat fluxes coming from AC systems were responsible of an increase in the air temperature up to 1.5–2 °C in some dense urban areas. Effects of modifications in the roof albedo and building material properties reduced the total EC by 4.8 and 3.6%, respectively, affecting the intensity of the UHI. When AC systems were not ejecting the heat fluxes out in the atmosphere, the EC was reduced to 2.5%. Copyright © 2011 Royal Meteorological Society