Chao Ren

Improving the wind environment in high-density cities by understanding urban morphology and surface roughness: A study in Hong Kong

Abstract In this study, a high-resolution frontal area density (FAD) map that depicts the surface roughness of urban Hong Kong is produced using a mapping method that takes into account the dense urban morphology and the site wind availability of the territory. Using the MM5/CALMET model simulated wind data of Hong Kong, the FAD map of three urban zones are calculated: podium (0–15m), building (15–60m), and urban canopy (0–60m). The wind tunnel test data is used to correlate the FAD understanding of the three zones. The grid sensitivity test indicates that 200m×200m is the reasonable resolution for the FAD map; the test also establishes that the lower urban podium zone yields the best correlation with the experimental data. The study further establishes that the simpler two-dimensional ground coverage ratio (GCR), which is readily available in the planning circle, can be used to predict the areas average pedestrian level urban ventilation performance of the city. Working with their inhouse GIS team using available data, it allows the planners a way to understand the urban ventilation of the city for decisions related to air paths, urban permeability and site porosity.

Effect modification of the association between short-term meteorological factors and mortality by urban heat islands in Hong Kong.

Background Prior studies from around the world have indicated that very high temperatures tend to increase summertime mortality. However possible effect modification by urban micro heat islands has only been examined by a few studies in North America and Europe. This study examined whether daily mortality in micro heat island areas of Hong Kong was more sensitive to short term changes in meteorological conditions than in other areas. Method An urban heat island index (UHII) was calculated for each of Hong Kong’s 248 geographical tertiary planning units (TPU). Daily counts of all natural deaths among Hong Kong residents were stratified according to whether the place of residence of the decedent was in a TPU with high (above the median) or low UHII. Poisson Generalized Additive Models (GAMs) were used to estimate the association between meteorological variables and mortality while adjusting for trend, seasonality, pollutants and flu epidemics. Analyses were restricted to the hot season (June-September). Results Mean temperatures (lags 0–4) above 29°C and low mean wind speeds (lags 0–4) were significantly associated with higher daily mortality and these associations were stronger in areas with high UHII. A 1°C rise above 29°C was associated with a 4.1% (95% confidence interval (CI): 0.7%, 7.6%) increase in natural mortality in areas with high UHII but only a 0.7% (95% CI: −2.4%, 3.9%) increase in low UHII areas. Lower mean wind speeds (5th percentile vs. 95th percentile) were associated with a 5.7% (95% CI: 2.7, 8.9) mortality increase in high UHII areas vs. a −0.3% (95% CI: −3.2%, 2.6%) change in low UHII areas. Conclusion The results suggest that urban micro heat islands exacerbate the negative health consequences of high temperatures and low wind speeds. Urban planning measures designed to mitigate heat island effects may lessen the health effects of unfavorable summertime meteorological conditions.

Classification of Local Climate Zones Using ASTER and Landsat Data for High-Density Cities

The local climate zone (LCZ) scheme provides a standard method to conduct urban heat island studies, in which urban landscapes are classified into different LCZs according to urban structures, land cover, and construction materials. Based on the LCZ classification scheme, the World Urban Database and Access Portal Tools (WUDAPT) is a new initiative to generate LCZ maps of cities worldwide with the use of freely available Landsat data. This paper aims to evaluate the performance of the original WUDAPT method in LCZ mapping for high-density cities. To further improve LCZ mapping accuracy for high-density cities, we investigate the usage of both freely available Landsat and advanced spaceborne thermal emission and reflection radiometer (ASTER) satellite data to generate better LCZ mapping results. Experiments on two high-density Chinese cities, Guangzhou and Wuhan, showed that combining Landsat and ASTER data can improve the overall performance of LCZ mapping results, especially for urban areas. This finding indicates that further applications of the WUDAPT method for high-density cities can include both ASTER and Landsat data.

Mapping the urban microclimatic spatial distribution in a sub-tropical high-density urban environment

Understanding the urban microclimatic spatial distribution and its impact on thermal comfort is important for integrating climatic consideration into urban design process. This article presents a case study in Tsim Sha Tsui and Tai Po of Hong Kong densely built-up areas to investigate the spatial distribution of microclimatic condition. Air temperature (Ta), wind speed (v), relative humidity (RH) and globe temperature (Tg) of 87 locations in two selected sites were measured on a summer day and a winter day respectively. Physiological Equivalent Temperature was calculated to analyse the thermal comfort condition in two sites. Both numerical simulation and geographical mapping approach were used for the estimation of the microclimatic spatial distribution. Results show that the influence of urban morphology on the microclimatic spatial distribution can be well investigated by using numerical simulation while geographical mapping based on measured data shows higher estimation accuracy due to the consideration of anthropogenic heat and other factors associated with human activities. In summary, this article presents a pragmatic approach of mapping the urban microclimatic spatial distribution that can be referenced by architects and urban designers to raise climatic considerations for designing better cities.

China's adaptation to climate & urban climatic changes: A critical review

Abstract Since the conclusion of the 2014 Climate Summit in New York and the 21st Conference of the Parties (COP21) in Paris, China has been actively advancing its national policies on climate change mitigation and adaptation since more unpredictable extreme weather events are expected, which may incur a heavy cost in terms of economics and public health. Since China is still in the process of urbanisation, the greatest challenge it faces is finding a balance between economic growth and keeping carbon dioxide and greenhouse gas emission rates at a manageable level. Cities in China play a key role in the implementation of the central policies and make concrete actions in response to climate change. With reference to a series of recent policy papers and action plans as the background, this paper attempts to provide a critical overview of Chinas climate change action plans from the national to the city and urban level. It seeks to understand whether the proposed responses to climate change and strategies for actions on greening and air corridors for cities and urban areas are appropriate. It is found that for China to advance its urban climatic adaptation strategy there is a need for (1) urban data, (2) a cross-disciplinary impact assessment, and (3) the development of a market and policy transformation mechanism.

World Urban Database and Access Portal Tools (WUDAPT), an urban weather, climate and environmental modeling infrastructure for the Anthropocene

Capsule Summary:WUDAPT, an International community generated urban canopy information and modeling infrastructure (Portal) to facilitate urban focused climate, weather, air quality, and energy use modeling application studies.

Characterizing prolonged heat effects on mortality in a sub-tropical high-density city, Hong Kong

Extreme hot weather events are likely to increase under future climate change, and it is exacerbated in urban areas due to the complex urban settings. It causes excess mortality due to prolonged exposure to such extreme heat. However, there is lack of universal definition of prolonged heat or heat wave, which leads to inadequacies of associated risk preparedness. Previous studies focused on estimating temperature-mortality relationship based on temperature thresholds for assessing heat-related health risks but only several studies investigated the association between types of prolonged heat and excess mortality. However, most studies focused on one or a few isolated heat waves, which cannot demonstrate typical scenarios that population has experienced. In addition, there are limited studies on the difference between daytime and nighttime temperature, resulting in insufficiency to conclude the effect of prolonged heat. In sub-tropical high-density cities where prolonged heat is common in summer, it is important to obtain a comprehensive understanding of prolonged heat for a complete assessment of heat-related health risks. In this study, six types of prolonged heat were examined by using a time-stratified analysis. We found that more consecutive hot nights contribute to higher mortality risk while the number of consecutive hot days does not have significant association with excess mortality. For a day after five consecutive hot nights, there were 7.99% [7.64%, 8.35%], 7.74% [6.93%, 8.55%], and 8.14% [7.38%, 8.88%] increases in all-cause, cardiovascular, and respiratory mortality, respectively. Non-consecutive hot days or nights are also found to contribute to short-term mortality risk. For a 7-day-period with at least five non-consecutive hot days and nights, there was 15.61% [14.52%, 16.70%] increase in all-cause mortality at lag 0–1, but only −2.00% [−2.83%, −1.17%] at lag 2–3. Differences in the temperature-mortality relationship caused by hot days and hot nights imply the need to categorize prolonged heat for public health surveillance. Findings also contribute to potential improvement to existing heat-health warning system.

Beyond the urban mask

Despite the great importance of cities, relatively little consistent information about their internal configuration (structure, cover and materials) is available. The World Urban Database and Access Portal Tools (WUDAPT) initiative aims at the acquisition, storage and dissemination of data on the form and function of cities indifferent levels. At the lowest level, the Local Climate Zone (LCZ) scheme provides a basic description of urban structure. This scheme is a climate-based typology of urban and natural landscapes that also provides relevant information on basic physical properties of the landscape, which can be used in modelling and observational studies. The LCZ scheme has large potential as a standard generic description of urban areas. In this paper the scheme and our standard mapping approach are presented, followed by recent improvements and research on object-based image analysis, transferability of trained LCZ classifiers, quality of crowd contributions, and the use of other data sources and methods.

Defining the environmental performance of neighbourhoods in high-density cities

ABSTRACT The regenerative design framework aims to ‘engage a broader range of possibilities by moving beyond the immediate building and site boundaries’. It implies that the environmental performance of buildings requires a revised definition so that it considers not only the building itself, but also its contribution beyond its own boundary, i.e. neighbourhoods. In high-density cities, outdoor spaces are culturally considered as the extension of one’s living spaces. The environmental performance of neighbourhoods is particularly important to the health and wellbeing of urban inhabitants. This paper aims to define the environmental performance of neighbourhoods in high-density urban context based on the experience acquired in previous studies in Hong Kong over the last 15 years. These studies cover a wide range of environmental issues including urban climate, outdoor thermal comfort, and daylighting design in high-density cities. Subsequent development of the assessment tools for environmental performance of neighbourhoods in Hong Kong is also presented. The framework of stakeholder engagement, as an integral part of the neighbourhood assessment tool, is discussed. This paper highlights the distinctive features of the environmental performance of neighbourhoods in high-density urban context and how it influences the professional practices in Hong Kong.

Investigating the relationship between Local Climate Zone and land surface temperature

The concept of Local Climate Zone (LCZ) has been developed to quantify the correlation between urban morphology and urban heat island (UHI). Each LCZ is supposed to have homogenous air temperature. However, traditional air temperature observation methods have limited spatial coverage and poor spatial resolution. Land surface temperature (LST) acquired from satellite images can be used to study the temperature characteristics of LCZ classes by providing continuous data on surface temperature. This study aims to study the relationship between LST and LCZ classes with Shanghai selected as a case study because of its high urbanization rate and serious UHI effect. This study has three major steps: Firstly, Shanghai local climate zone map was generated using the World Urban Database and Portal Tool (WUDAPT) method. Secondly, a remote sensing approach was taken to acquire Shanghais LST from night-time Aster thermal data in different seasons. Thirdly, the LST was associated with the Shanghai LCZ map and the correlation between LCZ and LST in Shanghai was discussed. The results show that there are large variations in LST across LCZ classes in different months in Shanghai. These results will be able to offer integrated information under urban climate principles for urban planners and urban climate researchers.