Towards planning and practical understanding of the need for meteorological and climatic information in the design of high-density cities: A case-based study of Hong Kong



More than half the world's population lives in cities. In tropical and subtropical regions, the growth of mega and compact cities are on the rise. The urban climatic issues of heat, humidity, lack of daylight, solar access, and urban ventilation is of topical concern to urban planners and governments. This paper puts forward a notion that a well established view of the low impact of urban climate on planning may be due to the lack of planning on the part of urban climatologists. Overly detailed and precise meteorological information, and excessively sophisticated climatic explanations and knowledge presentation do not help planners; information overload makes planners feel discouraged and ill equipped. In this paper, the understanding of Hong Kong based on the scale of planned decision making is elaborated with examples. Urban climatic information must be presented sequentially to fit the hierarchal process of planning and land use decision making. For better transfer of knowledge and communication, ‘prevailing’ and ‘criticality’ should be observed; information overload must be avoided, and spatial information must be presented graphically whenever possible. Scholars have argued that instead of the need for precision and accuracy, most of the time planners need to make balanced and reasonable decisions. Simplicity is the key. Furthermore, the advent of rapid urbanisation in the age of climate change further endows urban climatologists the burden to develop appropriate and easy-to-understand urban climate knowledge for planners. Resolving something complicated into something simple for planners is the only way forward. Copyright © 2011 Royal Meteorological Society

1. Toward mega, compact, and habitable cities

Since 2006, more than half the world's population have lived in cities (UNFPA, 2009). The number of cities and megacities is on the rise; the urban population, especially in Asia, is on the rise as well. There are now more than 20 megacities (i.e. cities with population of more than 10 million) on Earth. More cities are being added to the list. In addition, more than 400 cities now have populations in excess of 1 million. The conversion rate of agricultural land and rural areas into concrete-paved and tarmac-sealed land, especially in rapidly developing regions such as China, is increasing (Seto and F ragkias, 2005). The United Nations estimated that the urban population in less-developed countries would rise from 0.5 to 3 billion by 2030. Urbanisation and higher-density living is now an irreversible trend of human urban development (UNFPA, 2009).

There are commercial and political reasons for high-density living in mega and compact cities (Walker, 2003). Higher density and more compact city designs conserve valuable land resources, reduce transport distance (and consequently, the energy needed), and make public transport more viable (Smith, 1984; Betanzo, 2007). Advocates argue that high-density cities are more economically efficient. There are, of course, downsides and concerns (Phoon, 1975), such as the stress of crowed living and ‘high density, low diversity’ (Freedman, 1975; Travers, 1977). Doubtless, concerns are mostly based on past unhappy episodes of squatters, high-rise council flats, and slums. Nonetheless, the need for appropriate designs for high-density cities is clear. Designs that take urban climate into consideration are puzzling agenda for planners and urban climatologists.

Mega and high-density compact cities suffer from large conglomerates of urban land mass with high thermal capacity and urban heat island intensity (Oke, 1973). In addition, they have higher ground roughness and poorer urban ventilation (Landsberg, 1981; Oke, 1987). High anthropogenic heat and pollution emissions are also problems under weak synoptic wind conditions (Taha, 1997; Hamilton et al., 2009; Narumi et al., 2009). High-density compact cities, by their own urban morphological nature, have tall and bulky buildings, which lead to high frontal area density, high building-height-to-street-width ratio, restricted sky view factors, and low solar access (Yamashita et al., 1986). They are also lacking in open and green spaces (Jim, 2004).

Urban landscape creates an urban climate that affects human comfort and environmental health (Tzoulas et al., 2007; Poggio and Vrščaj 2009). Generally, the use of climatic knowledge in land use and urban planning is lacking (Oke, 1984; Pressman, 1996). Planners and policymakers either do not pay sufficient attention to this increasingly important issue, or cannot fully engage the missing link. Understanding this lack of integration between urban climatic and urban planning knowledge is important, especially for planners of mega, high-density, and compact cities (de Schiller and Evans, 1996; Evans and de Schiller, 1996; Scherer et al., 1999; Eliasson, 2000).

Many mega, high-density, and compact cities are located in tropical and subtropical Southeast Asia, which have hot and humid climatic conditions (Table I) (Roth, 2007). Many of these cities are on the coastline. Past ill planning in Hong Kong has resulted in tall buildings that limit incoming sea breeze to inland areas (Ng et al., 2009). For cities next to hills, vegetation is not protected, resulting in lesser katabatic wind and air mass exchange benefits. Cities situated in the basin suffer from low wind penetration and higher air pollution, especially when important air paths through the city are blocked (Mayer, 1999).

Table I. Some examples of mega and compact cities in topical and sub-tropical Southeast Asia, and their key urban and climatic characteristics
CityContextPopulation (millions)Urban area (KM2)Mean summer air temperature ( °C)/RH (%)Max. UHI 
  1. c: Coastal.

  2. l: Inland.

  3. v: Basin.

  4. h: Hilly.

Manila, Philippinesc20142528/90%3Tiangco et al., (2008)
Mumbai, Indiac2177730/85% 
Gugngzhou, Chinal12259029/83%6Jiang et al., (2007)
Jakarta, Indonesiac24272027/92% 
Taipei, Taiwanl, v, h744028/91%6Lin et al., (2008)
Singaporec4.547927/79%7Chow and Roth, (2006)
Hong Kongc, h727228/80%8Nichol, (2009)
Kula Lumpur, Malaysial, h6213727//95%8Mohammed, (2004)
Bangkok, Thailandl9150229/91%3.5Boonjawat et al., (2000) and Elsayed, (2006)
Dhaka, Bangladeshl1034429/79% 

In mega, high-density, and compact cities located in the tropical and subtropical region of Southeast Asia, heat-stress-related mortality and morbidity is on the rise (Yan, 1997, 2000; Yip et al., 2006; Leung et al., 2008; Chan et al., 2010). This has raised the alarm for local politicians and city planners. Given the inevitable event of global warming and extreme weather, health implications of increasing urban heat stress in cities is of topical concern (McGeehin and Mirabelli, 2001; Kovats and Jendritzky, 2006). Heat waves are becoming more frequent, longer in duration, and higher in intensity. One study in Hong Kong has indicated that the occurrence of ‘heat spells’—defined as 6 continuous very hot days (Tmax over 33 °C) and counting from the first day of the occurrence—can increase from 11 to 97 times under a UHI of 3 °C in the daytime. The increase of very hot nights (Tmin over 28 °C) from 10 to 127 times has also been reported under the same UHI conditions. In a nutshell, with 3 °C of UHI, inhabitants of the city would live almost every day and night under high thermal heat stress during the summer (Ng, 2009). Apart from the impact to health, higher urban temperature also means higher energy consummation for air conditioning (Fung et al., 2006), thereby increasing energy use and CO2 emission.

Noting the inevitable implications of urban climatic issues on health and comfort, the green and sustainable movement for city planning has gathered momentum in recent years. Since 2002, the Cabinet in Tokyo has had a general task force comprising the ministries concerned to address such issues. In 2005, the Hong Kong government established the First Sustainable Development Strategy for Hong Kong; in 2006, it launched the Feasibility Studies for the Establishment of Air Ventilation Assessment System. Since 2004, the Singaporean Government has been finding ways to understand these problems and has attempted to address them by commissioning various studies (Wong, 2004; Jusuf et al., 2007). Since 2005, the city government of Taipei has begun to pay attention to these same problems (Lin et al., 2005; Lin et al., 2008). At least for some quickly urbanising areas, political will is present; only the methods remain to be a concern for the planners and the politicians.

2. The Missing Link

Very few planners are familiar with the work of Luke Howard (1772–1864). However, planners would most likely know Sir Ebenezer Howard (1850–1928) and the details of his contribution to garden city and modern urban and land use planning (probably in good urban climatic sense cloaked in planning language). Sir Ebenezer's three-magnet-diagram mentions ‘foul’ and ‘pure’ air, ‘murky sky,’ ‘bright homes and gardens,’ and ‘no smoke’ (Howard, 1902). Sir Ebenezer knew and probably had read what Luke Howard discovered and published in his book, The Climate of London, in 1818 (Howard, 2009). Luke Howard vividly wrote his observations of the sky and air of the city of London. He describes the situation as ‘this volcano of a thousand months would, in winter be scarcely habitable.’ Apart from Luke Howard's understanding of the sky and air of the city of London, he has also been attributed to be one of the first, if not the first, to have noted that urban temperature is higher than rural temperature (Howard, 1833). This is now known as the urban heat island intensity (UHI). In hindsight, the garden city movement of Sir Ebenezer is perhaps the best solution to the problem that planners face today.

Landsberg, in the preface of his book, The Urban Climate, wishes that the text ‘will not only be useful for boundary layer meteorologists, but also for city planners and developers …’ (Landsberg, 1981). Unfortunately, 30 years on, the number of planners and developers who are familiar with even the title of the book, let alone the content of urban climate knowledge essential to planning-related decision making, remains small. Eliasson observes that, although planners may claim an interest in urban climate, the use of climate knowledge in their work is unsystematic and has a low impact on the planning process (Eliasson, 2000). She attempts to outline the missing link based on five explanatory variables: conceptual and knowledge-based, technical, policy, organisation, and the market. The onerous task, she reckons, is for urban climatologists to provide suitable methods and tools to the planners, and not, as typically argued, for planners to learn from urban climatologists. Echoing Eliasson in the 2009 World Climate Conference 3, Grimmond and Mills have presented two papers that gather the views of over twenty international co-authors (Cleugh et al., 2009; Grimmond et al., 2009). The authors argue that there is a ‘technical’ need for information especially for fast-growing cities and mega cities in the tropics and subtropics. There are also ‘communication’ needs for programs and dialogues. More importantly, Mills calls for an integrated hierarchal model that can address planning needs at various planning scales. This is an important acknowledgement by urban climatologists that planning is a hierarchal process that sequentially deals with issues based on an important working parameter called ‘scale.’ This demands from urban climatologists an appreciation of the kind of urban climatic information that must be tailored for various scales of planning. Hence, avoiding information overload is crucial as it has the inevitable side effect of causing planners to believe, as Eliasson observes in her study, that they are not well equipped (Eliasson, 2000).

3. Disserting the missing link with reflective practice

To further understand the missing link, an investigation protocol commonly known in the design field as ‘reflective practice’ is used. The concept was introduced by Donald Schön (Schön, 1983; Schön, 1985), and is based on an older conceptual protocol known as the Mediation of Marcus Aurelius (Mac Suibhne, 2009). A planner himself, he understands the thinking process of professionals especially under new and uncharted circumstances. He realizes that professionals seldom follow technical rationality as the grounds of professional knowledge. Bryant (Bryant et al., 1997) appropriately sums up the crisis Schön identifies: Technical rationality is a positivist epistemology of practice. It is ‘the dominant paradigm which has failed to resolve the dilemma of rigor versus relevance confronting professionals.’ Schön notes that design professionals work by referring to a repertoire of metaphors and images that allow for different ways of framing a situation. The repertoire of known metaphors and images provides what Schön sees as the ‘stable state,’ which practitioners seldom cross. Unless new information can be framed within the repertoire, the information is more likely to be overlooked (Schön, 1973). The beginning paragraphs of Section 2 in this paper about the two Howards illustrate this mismatch.

Reflective practice means that one studies one's own working process critically to understand what can be improved. The process is associated with learning from experience and is an important strategy for lifelong learning. There are typically three phrases of reflective practice: ‘reflection for action,’ ‘reflection in action,’ and ‘reflection on action’ (McAlpine and Weston, 2000). ‘Reflection in action’ is likely the more suitable protocol used as the disserting tool in this study. Since 2003, the author of this study has worked ‘reflectively’ with city planners of the Planning Department of the Hong Kong Government on a number of projects. They range from the district level land use planning, new town planning, to the urban level and site-level planning where urban climatic issue is regarded as a concern by top government officials and politicians. The working process has allowed for observations that may shed light on the so-called missing link.

4. From meteorological observations to urban planning

The starting point of all urban climatic understanding of urban planning typically begins with meteorological information from local observatories. Meteorological observations (e.g. air temperature, rainfall, wind speed, and relative humidity) are routinely collected by meteorological services at stations around the world at quarter-hourly or shorter intervals (WMO, 2003) to monitor weather conditions in both synoptic and local scales. Data of weather stations with long periods of observation provide climatic information for a specific area, and are essential for planners and architects to understand its ‘prevailing’ and ‘critical’ climate conditions. Moreover, meteorological data depicting ambient climate conditions are often used in downscaling studies and spatial evaluation of data related to detailed urban planning, building design, and environmental impact assessments.

When assessing climatic information, the key words for planners are ‘prevailing’ and ‘critical’; these translate to ‘how often’ and ‘how important’, respectively. The ‘how often’ aspect of information is normally well presented in tables and diagrams; unfortunately, the ‘how important’ aspect of the information is typically missing. Rather than knowing the average air temperature in the month of July, understanding the human-biometeorological implications is more important to planners. Hence, overlaying basic climatic information with human-biometeorological information (Figure 1) is far more useful (Cheng and Ng, 2006). The consequences of urban climatic conditions that fall outside the human-biometeorological threshold should also ideally be stated and explained to planners when climate information is presented (Li and Chan, 2000; Yan, 2000; Yip et al., 2007; Chau et al., 2009). Most importantly, to avoid information overload, information should be presented in a simple and sequential manner to fit the hierarchal process of planning and land use decision making.

Figure 1.

The monthly minimum, average, and maximum air temperatures are graphed. It is then overlaid with the human biometeorological comfort zones of the locals after taking into account human acclimatisation. The importance of wind for the summer months of June–August is highlighted. The important message to the planners is that urban wind must be optimised. This figure is available in colour online at

For air temperature, monthly air temperature of the Hong Kong Observatory coupled with the human-biometeorological threshold of local inhabitants taken from user survey data reveal that, in the months of May and September, daytime maximum air temperature can be a problem (Figure 1). Planners have learned that ‘critically,’ every 1 °C beyond the threshold can mean an increase of four times the incidence of heat-stress-related mortality (Leung et al., 2008). Designing the city to limit daytime maximum heat island to within 2 °C, while simultaneously maximising urban wind to the order of one meter per second is crucial. By themselves, these simple objectives allow planners and politicians to realize the goal. This is the situational metaphor, as identified in Section 2 of this paper, which design professionals need. In this case, criticality of the images includes heat-related mortality issues. Furthermore, planners in Hong Kong should also focus on ‘prevailing’ issues in terms of timing (i.e. in the months of June to August). During the working process with planners, climatic terms, such as air temperature, wind speed, and so on, have little meaning in terms of planner mental metaphors and images. These have to be constantly brought back to concerns of criticality that have social and economical implications. Otherwise, little of the meteorological data would make sense to planners, let alone to politicians who often direct what planners should or should not do.

5. The planning process

During the observation period of working with planners, the need for planners and architects to understand how climate information can be usefully incorporated into decision making is realized (Chandler, 1976; de Schiller and Evans, 1996). Climatologists, in turn, need to appreciate the work pf planners and architects in design. For planners, a plan is a systematic arrangement, configuration, or outline of elements (such as buildings and their related functions) or important parts (land use zones, like roads and open spaces) for the accomplishment of an objective. Professionals dealing with the built environment need to bridge a very large spatial and time scale difference of understanding (Oke, 2006). In addition, multiple, and sometimes contrasting, data have to be reconciled. Most of the time, a compromise, and not an optimised result, emerges. Indeed, planning is a political process that needs to balance the interests of different stakeholders and factors. Most of the time, there is a need to strike a reasonable solution, rather than an accurate or precise one. Scientists commonly find this unscientific manipulation and balancing act by planners difficult to appreciate. Borrowing from Schön's theory of reflective practice, a big difference is observed in the repertoire of known metaphors and images of framing a situation between a design professional dealing with complicated ‘wicked’ problems (Table II) (Rittel and Webber, 1973) and an urban climatologist wishing for precision and definitive solutions.

Table II. Rittel and Webber's ten characteristics of wicked problems of planning, (Ritchey, 2007)
1. There is no definitive formulation of a wicked problem.
2. Wicked problems have no stopping rule.
3. Solutions to wicked problems are not true or false, but better or worse.
4. There is no immediate and no ultimate test of a solution to a wicked problem.
5. Every solution to a wicked problem is a ‘one-shot operation’; because there is no opportunity to learn by trial and error, every attempt counts significantly.
6. Wicked problems do not have an enumerable (or an exhaustively describable) set of potential solutions, nor is there a well described set of permissible operations that may be incorporated into the plan.
7. Every wicked problem is essentially unique.
8. Every wicked problem can be considered to be a symptom of another problem.
9. The existence of a discrepancy representing a wicked problem can be explained in numerous ways. The choice of explanation determines the nature of the problem's resolution.
10. The planner has no right to be wrong (planners are liable for the consequences of the actions they generate).
1. The solution depends on how the problem is framed and vice-versa (i.e. the problem definition depends on the solution)
2. Stakeholders have radically different world views and different frames for understanding the problem.
3. The constraints that the problem is subject to and the resources needed to solve it change over time.
4. The problem is never solved definitively.

Examining the planning process further reveals three process scales in Hong Kong (Cullingworth and Nadin, 2006) and, commonly, in other places in the world: regional, district, and master layouts. The decisions and climatic information required are different in each of the three stages.

6. Regional planning

Typically, regional planning in the form of territorial or country plans involves a spatial scale of tens or hundreds of kilometers or larger, and with decision time scale implications of 10–30 years, and a map scale in the order of 1:20 000 or larger. In the past, planners planned the future of an area by mostly addressing socio-economic needs. They made decisions in terms of land use, development density, transportation, resources, and energy flows; all of which take into account characteristics of the region and the infrastructural constraints. The political aspirations and values of citizens allowed prioritisation of various factors to be considered; these affected the outcome of planning. For example, town planners commonly proposed a plan in the year 2000 for 2030 with a sub-text of ‘towards a city of 10 million,’ ‘a better connected social network,’ or ‘sustainable eco-city.’ In the past, ‘climate information’ was rarely seriously considered when planning at this strategic level. A number of reasons underlined this lack of consideration. First, climate was considered a ‘constant’ entity. The advent of the issue of climate change (IPCC, 2007) and a better understanding of UHI (Mills, 2005) and other urban climatic issues are slowly changing the perception or repertoire of known metaphors and images of framing a situation. Furthermore, the political quest for sustainability and energy efficiency has somehow required planners to find ways to address issues and explain plans accordingly to the public. There is a need to appreciate the changing climatic boundary conditions of planned areas. Second, climate was not perceived to be an important issue because there were more pressing socio-economical needs and wishes. Public perception is slowly being altered due to an increased awareness of environmental concerns (Evans and de Schiller, 1996).

In Hong Kong, government planners have developed the 2030 strategic plan (Figure 2), and sustainability and city design have been mentioned in the working process. The planning keywords are ‘infrastructure capacities’ in terms of the environment, ‘quality living space’ in terms of urban spaces and environment, ‘air quality’ in terms of emission and dispersion, and ‘waste management and energy consumption’ in terms of resources management. Regardless of the parametric concerns of planning, in spatial design (i.e. laying down the morphology of the future city on paper), the need to spatially appreciate concerns is ever-present; issues of ‘prevailing’ and ‘criticality’ are already assumed. How should urban climate at this scale be presented spatially, with both notions incorporated?

Figure 2.

The recommended development plan under Hong Kong 2030 planning vision and strategy (HKGSAR, 2007b). This figure is available in colour online at

Climatic maps (klimaaltas) are powerful and, more importantly for planners, more easily understood visual tools. The method originated in Germany (Mayer, 1988; VDI, 1997; Scherer et al., 1999), and is now popular in other places in the world (Alcoforado, 2008). Earlier climatic maps were hand drawn; however, lately, the use of Geographic Information System (GIS) has become common. The climatic map synthesises various kinds of climatic, topographic, and urban morphological information into synergetic understanding (Figure 2). Human-biometeorology, urban noise, and air pollution interpretations based on these maps can be formulated. When necessary, mitigation measures can be detected and planned at the regional spatial scale.

The making of a climatic map relies on a careful collection and collation of available meteorological data from the National Meteorological and Hydrological Service (NMHS). Long-term air temperature, precipitation, wind, cloud, and solar radiation data are input into the map and evaluated. The Berlin Digital Environmental Atlas contains eleven layers of information on climate ranging from ‘long-term mean air temperature’ to ‘bioclimate day and night.’ The Hong Kong Urban Climatic Map has nine layers of information on climate and planning ranging from wind formation to building volume and building ground coverage (Ng et al., 2009).

In making the urban climatic map, supplementing observed meteorological data with simulation and experimental data (Schirmer, 1984) is necessary. Meso-scale models (e.g. MM5) have been used. Some simulations involve a nesting strategy to bring the resolution down to a few hundred meters and, parametrically, at the urban canopy level. Use of the prognostic model FITNAH for the Berlin Atlas; the Urban Canopy Simulation System (UCSS) for the Tokyo Environmental Map; and the MM5/CALMET model for Hong Kong (Figure 3) are examples. The crucial step is to simplify results of the model simulation for planning. In Hong Kong, rather than presenting complicated wind rise and frequency information of wind availability, only the prevailing wind direction in the summer months is extracted. This represents the critical condition for planning to try to make a reasonable decision.

Figure 3.

A simulation in July 2004 showing the prevailing wind directions representing the critical summer month conditions of Hong Kong using MM5/CALMET simulation model. (Graphics, courtesy of Professor Jimmy Fung of Hong Kong University of Science and Technology. The figure is provided to the author as part of the urban wind environment study for planning in Hong Kong). This figure is available in colour online at

In some cases, tracer gas experiments, wind tunnel tests, and mobile traverse air temperature measurements are conducted in monitoring stations in the city, mostly in the form of short-term case-based studies. Currently, due to the sparse data density of weather observing networks (mostly not within the city) and the expense of conducting field case studies, the case-based data could at best be described as ‘snapshots,’ and may not be entirely robust both for its representativeness and for post-design evaluation purposes. For planners, without long-term site-specific meteorological records, snapshots in critical conditions are still the ‘no-better-alternative’ solution. Again, the information is useful for making ‘reasonable’ planning decision.

At this scale of climatic understanding, planners need to first discern ‘the general patterns,’ such as the generic climatic zones, the regional wind directions, the locations of the breeze-way, and the major air mass exchange routes. Second comes the ‘important issues’ of climate of the city. These typically do not need to be too exact or detailed. This is very important to appreciate because urban climatologists or scientists have a tendency to provide too much complicated information, which could overload the planners too early in the process. As explained, providing 12 monthly wind-rise values may be scientifically accurate; however, the planners need only to have the prevailing wind flow of an area in critical times for their work. Basing on results of model simulation, and with reference to the observatory data in Hong Kong, planners and urban climatologists sat down and made a simple interpretation of wind dynamics of the city and produced the Wind Information Map of Hong Kong (Figure 4). This map is an evaluated simplification of the observed and model-simulated data into a generalised understanding for planning.

Figure 4.

The Wind Information Map of Hong Kong. The complex understanding of model simulation and the wind roses of over 40 observatory stations have been synthesized to allow planners an easy overview of the more critical wind flow pattern of the territory. This figure is available in colour online at

For planners, the ‘criticality’ of climatic information is important. Rather than simply showing the variations of daily/monthly air temperature in tables and graphs, planners need to see the relevance of data if the ‘how important’ of the data is represented. Researchers in Japan (Masumoto, 2009) have calibrated air temperature data into hot days and nights. As such, planners have a clearer map-based spatial picture of the consequences of air temperature data and are in a better position to act when there is a need to address the issue from a political and planning point of view. In Hong Kong, the urban climatic analysis map classifies territory into eight classes using the human biometeorological assessment index, PET (Physiologically Equivalent Temperature), developed by Mayer and Höppe (1987). The urban climatic map takes into account building volume information, topography, and greening as the bases of the thermal load evaluation. The map also takes into account building ground coverage, ground roughness, and proximity to openness as the bases to evaluate the dynamic potential of the urban area in a 100 × 100 meter grid. Calibrations are conducted using field measurements and wind tunnel studies (Cheng et al., 2008; Ng et al., 2009; Ren and Ng, 2009; Chen et al., 2010), The eight classes are elaborated with explanations of their likely thermal and dynamic effects and planning actions needed (Figure 5). This spatially based urban climatic information is very useful to planners as it can be directly overlaid to strategic plans.

Figure 5.

The Urban Climatic Map of Hong Kong. The classes denote the predicted Physiological Equivalent Temperature (PET) differentials under typical summer daytime conditions. The map allows the planners an overview of the regional human biometeorological characteristics of the territory. Detail investigations (inserted diagram at the lower right) can be identified for their next stage of planning works. This figure is available in colour online at

Furthermore, consequential ‘urban parametric variations’ (i.e. what one should do and how much one needs to respond to) of climate information, even broadly speaking, is necessary. Knowing the density of buildings, even roughly, is important (Stone and Rodgers, 2001); percentage of ground coverage and greeneries may be balanced to achieve a desirable result given a certain understanding of intra-city air temperature variations. For subtropical summers of Hong Kong, to thermally mitigate the negative effects of high-density and bulky buildings in the city, 20–30% greenery is deemed to be reasonable, desirable, and practical (Wong, 2009; Wang and Ng, 2010). This information translating urban climatic understanding into a planning actionable understanding, rough as it may be, is more useful to architects, planners, regulators, and policymakers.

7. District planning

Once regional (territorial) planning is strategically developed, planners in Hong Kong and typically in other places need to zoom into the district level. The scale of operation is typically at the map scale of 1:5000 to 1:10000 and at the spatial scale of a few or tens of kilometers. In Hong Kong, this is the planning scale of the statutory Outline Zoning Plan (OZP). The plan is statuary and is the daily working plan of planners. OZPs show the proposed land-uses and major road systems. Areas covered by such plans are zoned for such uses as residential, commercial, industrial, open space, government, and comprehensive development areas. Attached to each OZP is a set of notes setting out the uses that are always permitted; otherwise, permission must be sought with the Town Planning Board. The explanatory statement reflects the planning intentions and objectives of the various land-use zones.

At this scale, the city structure, land use parcels, development density, building heights, and non-building areas, as well as infrastructural routes of transportation, can all be defined and mapped. A parametric understanding of the urban morphological characteristics is possible at this scale. Ground roughness length (zo), ground sealing percentage, tree area ratio, settlement extent and density, and anthropogenic input can all be estimated and planned. Coupled with this is a fundamental understanding of the climate of the locality and climatically conducive local natural settings, such as the surrounding mountains and the sea. In addition, the urban climatic characteristics of the district can be computed. Sophisticated computational fluid dynamics (CFD) techniques are available and, due to the recent increase of computational power, feasible. The input boundary conditions are normally based on the results of meso-scale modelling. Alternatively, they can be based on representative typical conditions likely to be of critical interest. A canopy closure model, or a simpler k-ε type model can be nested to provide more detailed urban, or even street-scale, information (Oguro et al., 2008); sub-grid scale urban elements can also be factored (Green, 1992; Hiraoka, 1993; Kikuchi et al., 2007; Mochida et al., 2008a, b). Guidelines for properly carrying out CFD are now available (Franke et al., 2004; Tominaga et al., 2008). Apart from CFD, the use of wind tunnels has commonly been employed to investigate urban ventilation and pollution dispersion, as well as air temperature fields of the urban environment (Kubota et al., 2008).

None of what has been explained would be of interest to planners. For planners, two levels of urban climatic information are typically needed. First is the ‘descriptive’ information of how a city behaves, preferably at a city scale and presented as a map (Figure 6). This allows planners a holistic appreciation of the urban climatic characteristics of the area. A very large-scale CFD (wind and thermal) study of Tokyo has recently been simulated within a five-meter-grid (Ichinose et al., 2003; Ashie et al., 2005). With this district-scale information, strategic decision of urban planning as to what needs to be done and where attention is needed can be elaborated; action plans can be formulated by the policymakers. In Japan, a kaze no michi (wind path) study has recently been conducted as a basis to revitalise an area near Tokyo Station (AIJ, 2008). In Hong Kong, based on the urban climatic map, a district 300 hectares of urban area (roughly the scale of one OZP in Hong Kong) has been wind tunnel- and CFD-studied to establish wind and urban ventilation characteristics. Basing on this information, street grids in newly planned areas can be better laid out (Figures 7 and 8).

Figure 6.

A district-based Large Eddy Simulation study of an urban area in Hong Kong (Weinreis et al., 2008). The district scale wind velocity ratios (the ratio of measured pedestrian level mean wind speed to the reference mean wind speed at a height of 400 m above sea level) have been presented. At this scale, for example, the important wind paths can be identified. This figure is available in colour online at

Figure 7.

The re-planning of the old airport site relies on urban climatic information input. The breeze-way directions proposed to the city planners based on CFD model simulation results (HKGSAR, 2007a). This figure is available in colour online at

Figure 8.

The re-planning of the old airport site relies on urban climatic information input. The green open spaces and their connectivity is a planning interpretation of the urban climatic needs (HKGSAR, 2007a). This figure is available in colour online at

Second, for planners, the ‘predictive’ and ‘parametric’ understanding of ‘if this, then that’ kind of causal relationship between a planning parameter and its consequential urban climatic and human biometeorological performance is what is important (Katzschner, 1998). Planners have in their scope the ability to alter only a few urban morphological parameters (e.g. land use and their arrangements, building density, design heights and dispositions, open spaces and greeneries, roads, and infrastructure). Urban climatologists and planners must work together to parametrically understand how to balance such parameters. In Hong Kong, tests have been conducted on how building ground cover, building density, and building heights with regard to urban climate can be parametrically understood for planners (Ng et al., 2003; Ng, 2007; Ng, 2008; Yoshie et al., 2008). Basing on this understanding, the optimal building site coverage, an important planning parameter, can be decided.

For planners, in addition to detail modelling and experimental or simulation studies, ensuring layman-level qualitative information of ‘do’s and don'ts' is important because planners have to find ways to explain a decision in jargon-free language to the general public and policymakers. Planning-related urban climatic guidelines are useful. In the city of Stuttgart, an urban climatic booklet has been published (Stuttgart, 2008). In Hong Kong, a set of urban climatic references has been incorporated into the Government Hong Kong Planning Standards and Guidelines (HKPSG, 2008) (Figure 9). Although they are mostly rule-of-thumb qualitative recommendations, they have proven to be of extreme value to councilors and lay board members when applying urban climate knowledge to planning and urban design decision making. For planners, councilors, and lay board members, a diagram is better than numbers, figures, or equations.

Figure 9.

A planning recommendation in Hong Kong Planning Standards and Guidelines to note the planners the possible design alternatives establishing and maintaining air paths in the city. This figure is available in colour online at

In many cities, ‘metro areas’ are developed ‘existing’ districts that require renewal and intervention. The planning process is slightly different because intervening within an existing urban area is politically difficult and expensive. The core of most mega and compact cities belong to this planning scope. Areas designed in the past were based on very different urban conditions of today. Many of the streets were not designed for cars (Abdul-Wahab and Al-Arairni, 2004); the living pattern and demography have changed; economics and citizen aspirations have risen; and most of the land has been built-up. Urban renewal plans have been necessary. How the urban climatic conditions can be improved to provide a quality living environment while respecting its current pattern remains a concern.

For planners, there is a need to understand the ‘needs,’ ‘wishes,’ and ‘perceived rights’ of existing stakeholders as to what quality environmental living is about, and how much effort/compromise they consider worthwhile. User survey and resident focus group discussions are needed. There is also a need to obtain comprehensive ‘as is’ urban climatic information of streets, spaces, and buildings to evaluate merits and deficiencies of the existing urban fabric. With this information, informed discussions with the stakeholders can be logically conducted. Again, there is a need for layman-oriented urban climate information.

Understanding of an existing district can be achieved with field measurements. Measurement programs such as these are expensive to mount. A recent study in Tokyo included mounting 190 weather observation points in an area of approximately ten square kilometers (AIJ, 2008). Case study information may be useful providing a sense of what is going on; for example, studies on urban air temperature, pedestrian-level air ventilation, micro-climatic, and intra-urban variations have been done in many cities that can provide planners with general references (Lazar and Podesser, 1999; Erell and Williamson, 2007; Ren and Ng, 2007; Wong et al., 2007). The more important concern is not data per se, but how data can be visually understood. In Hong Kong, urban ventilation and intra-urban air temperature field study results have been collated to become the Physiological Equivalent Temperature (PET) map, with associated planning recommendations (Figure 10). Again, information is best graphically represented. Figure 10 shows the new town area of Tuen Mun in the western part of Hong Kong, which has 600000 inhabitants living on a land area of approximately 10 square kilometers. The PET-devised district level planning recommendation map has defined five Urban Design Planning Zones (UDPZ). For example, UDPZ 5 contains the following guidelines:

Figure 10.

A district level planning recommendation map. Various urban climatic planning zones (based on PET understanding) have been identified spatially. A zonal understanding of urban climatic factors has also been spatially presented (B = breezeway, S = sea breeze areas, D = downhill air mass exchange areas, 1 and 2 = focused areas). This figure is available in colour online at

Very highly urban climatically sensitive area: (1) Mitigation actions are recommended and are considered essential; (2) These zones are very densely built. Thermal load is very high and dynamic potential is low. Very strong impact on thermal comfort is expected. A high frequency of thermal stress is anticipated; (3) Further adding of building volume and/or ground coverage is not encouraged and, if absolutely essential, should be carefully considered. Mitigation measures to ‘improve’ the existing conditions should be considered; (4) Existing air paths must be identified, respected, enhanced and widened. New air paths may need to be created. The prevailing wind directions and air mass movement must be considered when buildings are re-developed and re-positioned ‘to improve’ the existing situation. Strategic mitigation measures (air paths, open spaces, urban greenery, street widening, building setbacks, and so on) must be considered ‘to improve’ the existing situation; (5) A strategy to utilise all Government Institution and Community (GIC) sites to relieve the existing condition is recommended. No additional tall structure is encouraged on any of these GIC sites. Intensive greening is recommended; and (6) Addition greenery and tree planting on streets in these zones is essential and is recommended. Intensive greening in Open space (O) zones is strongly recommended.

Apart from the UDPZs, various district-based zonal understanding is also incorporated. For example, B on the map is the ‘breezeway zone’ and has the following planning recommendations: (1) Sea breezes from the waterfront are beneficial to Tuen Mun East and Tuen Mun South areas and must be respected; (2) Open spaces on the waterfront allow sea breezes to penetrate further inland. They must be retained with increased green coverage; (3) Developments near to and along the waterfront must be very carefully designed for urban air ventilation. In particular, developments along the waterfront must not form a continuous barrier to sea breezes. Buildings must be arranged and positioned so that sufficient gaps between building blocks are left for air ventilation and urban permeability. Ideally, building heights should be restricted so that only lower buildings immediately fronting the shoreline are allowed, enabling sea breezes to penetrate further inland. Site coverage of buildings on the waterfront should be reduced to allow larger air spaces at the pedestrian level for better air ventilation. Reduced podia, non-building zones within private development sites connecting with air paths, and setbacks along site boundaries are examples of useful design features; (4) Streets perpendicular to the waterfront leading into the urban areas, including Lung Mun Road, Wu King Road, Hoi Wong Road, Tuen Mun Heung Sze Hui Road, and So Kwun Wat Road, are important air paths. They must be maintained and, if possible, widened and landscaped; and (5) In addition, due to the cooler sea breezes, shaded and landscaped walkways along the waterfront are thermally neutral for human comfort in the summer months of Hong Kong. They are good design features of good resting and amenity spaces for the enjoyment of the city inhabitants. These provisions are recommended.

For planners, before and after urban climatic scenarios of an intervention are valuable. As such, there may be a need, before re-development is scheduled, to obtain data of the existing condition. The rather limited planning interventions permissible within the existing urban fabric should be considered, and any field measurements should be framed accordingly. There is little need for a full-scale scientific-oriented research. In Tokyo, there is a recommendation for large urban re-development to monitor on-site wind, air temperature, and relative humidity information at the pedestrian level for a year before and after building construction.

8. Master layout planning/building design

Further down the scale is the master layout planning at the neighborhood and building spatial scale of half a kilometer or less with a map scale of approximately 1:500 to 1:2000. This is typically referred to by urban climatologists as the urban canopy layer scale at the micro level (Oke, 2006) Many scholars have provided good understanding and design procedures (Page, 1976; Givoni, 1998; Szokolay, 2004; Emmanuel, 2005; Kwok and Grondzik, 2007). Observed climate data at this layout scale of planning and design normally do not exist, and one needs to rely on model simulations or experimental studies. The boundary conditions can be extrapolated from nearby meteorological data.

At the layout and building scale, for planners and architects, knowing the consequences of failure or non-action, or more positively, the advantages and ‘value-added-ness’ of a decision is necessary. Cost-performance studies are most useful. A priority list of actions can thus be stated. The economic and socio-economic benefits need to be stated as well. Urban climate information should be resolved and related to human comfort, health, human acceptance, and work productivity understanding.

In the past, the use of micro-urban and building-level simulation for environmental study was possible but uncommon (Augenbroe, 1992; Wong et al., 2000). This is slowly changing, especially in view of the need for building environmental assessments, such as LEED (Leadership in Energy and Environmental Design), in many project requirements. The site aspect portion of the assessment system typically requires an understanding of project impact to the surroundings. In Hong Kong, the BEAM+ system gives credits for projects that demonstrate good ‘neighborhood-ness’ by conducting Air Ventilation Assessment studies (Ng, 2009). Currently, the need to address the notion of ‘Zero Carbon’ development also requires designers to refer to climatic information as the basis for calculations.

At this scale, the consideration of alternative scheme designs and detailed design mitigation measures (Figure 11) are more crucial. Figure 11 shows the existing conditions versus the proposed design of the project site (two blocks of land in the centre of the figure) in terms of ground level urban ventilation. Given the high-density high-rise nature of the urban area, the CFD study demonstrates that the reduction of ground coverage of the proposed design allows for better urban ventilation. This is due to the fact that the proposed design has more air volume at the ground level and it has better connected air paths through the site.

Figure 11.

Two CFD model simulation studies of a dense and compact urban condition is Hong Kong. Showing the existing condition (left) and the proposed design (right), planners can evaluate the implication of a design. (Graphics, courtesy of Arup and Partners HK Ltd). This figure is available in colour online at

The Typical Meteorological Year (TMY) of a locality is commonly used by building service engineers as input to building performance simulations. This provides a ‘static’ and ‘typical’ baseline upon which designs could be studied. However, the dynamic and site-specific quality of the urban climate is not normally factored. For a closed-box, steady-state, air-conditioned artificial indoor environment, this may be fine; however, for designs that aim to use passive and natural means to create a more varied and diversified living environment both spatially and temporally, a static view of site level urban climate is hardly satisfactory. Currently, planners and designers are often assisted by building services and mechanical engineers. For the engineers to move outside the building envelope, input from urban climatologists may be needed. A dynamic study based on real-time or synthesised typical meteorological data on an hourly time step is needed to demonstrate, at the least, the percentage of time that the system may not work as designed. Given the ease and power of today's computers, this goal is practical and feasible.

9. Looking forward - cities of the future

For urban climatologist aiming to assist planners, the topical issue of a healthy, sustainable eco-city needs further thought. As part of the World Health Organization (WHO) Healthy Cities project, a guide to reorienting urban planning towards Local Agenda 21 entitled ‘Towards a New Planning Process’ has been published by the WHO Regional Office for Europe (WMO, 1999). Apart from the more conventional text on social and economic trends, an urban environment towards health for all has been emphasised. The need for human biometeorological design is now an important agenda for planners, not just for now, but also for the taking into account various changes, including climate change (Loveland and Brown, 1989; Smith, 2005; Isaac and van Vuuren, 2009).

At the regional and district scale of planning, the term ‘eco-city’ has increasingly been coined in many new town developments, especially in China and in Southeast Asia. One of the recent higher-profiled offering is the Dongtan eco-city project in China jointly promoted by the UK and the Chinese Governments (Wood, 2007). Climatic information has been factored for the design of buildings, open spaces, and the possibility of renewable energy production. Basing on the study, the potentials for zero- or low-energy neighborhood and architecture have been proposed. Another example is the Masdar eco-city in Abu Dhabi where wind information has been used to establish renewable energy potential, making planning scale and density of development possible (Masdar, 2010a, b).

At the layout and building design scale of planning is the advent of intelligent building information management system and clever electronics means that allow the building to find a way to actively engage changing weather on an hourly or instantaneous manner (Elmualim, 2009). A smart system may adjust windows and ventilation systems to cope with a possible change of weather in a few hours time, taking into account thermal lag and activity changes in the building (Lo et al., 2007). Estimating daylight availability and solar irradiation based on weather forecasts and the intelligent system can work out its light switching pattern, and cooling load needs also becomes possible (Ng et al., 2007). The next step is for NMHS to provide quality forecast of weather parameters in a pre-defined format for the system to self-calibrate and to work out a pattern. The possibility of adapting such innovations in refurbishment of a large share of existing building stock is similarly imminent for an overall improvement of the city.

Most importantly, there is a real need to plan a city to cope with climate change (London, 2002; IPCC, 2007). In Germany, the KLIMES project aims to ‘develop a set of guidelines and test its implementation in planning concepts with respect to the goal to achieve an improved climate protection of human beings under changing climate conditions and extreme weather events’ (Mayer et al., 2008). Climate adaptation strategies need to be established at the city planning level (ASCCUE, 2006; London, 2007). Basing on various global and regional climatic modelling, prediction, and scenarios, the future change in climatic parameters can be estimated and various likely-to-be-encountered critical issues are identified. More research and inter-disciplinary collaboration are required to investigate and ascertain the implications of climate change on urban planning (Burton, 1997; Adger et al., 2003).

10. Conclusion

Basing on a reflective in-action working process with planners and upon appreciating the wicked problem-solving nature of their work, the needs and the missing link between urban climate and city planning have been elaborated. Information requirements and data characteristics for planners have been explained. Some examples have been illustrated.

Urban climatic patterns at the regional planning scale in prevailing and critical conditions need to be understood by planners. Overall criticality needs to be stated so that planners can find ways to prioritise issues. Parametric understanding linking urban climate and urban morphology needs to be established. The urban climatic description of the urban fabric needs to be understood at the district scale of planning. Information in map forms is encouraged. Qualitative guidelines assisting planners to explain urban climatic matters to councilors and board members can be very useful. At the layout and building design scale, building services engineers must be assisted by urban climatologists to establish a more dynamic understanding of issues beyond the traditional closed-box approach. The advent of rapid urbanisation in the age of climate change further endows urban climatologists the burden to develop appropriate and easily understandable urban climate knowledge for planners. Resolving something complicated into something that is simple is the only way forward. Instead of the need for precision and accuracy, planners need to make balanced and, therefore, reasonable decisions. Simplicity is required from urban climatologists.

In her study, Eliasson notes the need for urban climatologists to provide planners with good arguments; this has been supported. The issue then is what defines a good argument. This paper presents the words ‘prevailing’ and ‘criticality’ to be foundations of such an argument. The term ‘prevailing’ gives laymen a sense of the frequency of occurrence and how often they are affected, whereas the word ‘criticality’ gives a sense of how important the issue is and what could be the implications.

For the issue of communication, this paper presents that keeping information simple and graphical is the key. An arrow on a map, albeit rough and imprecise, can be better for planners in the early district scales of the planning process. The advent of public awareness of issues related to climate change allows urban climatologists a platform to engage the public, stakeholders, and the government. This study is here to make a small contribution.

Planners and architects need to be trained more thoroughly in sustainability and environmental designs (de Schiller and Evans, 1996). The Royal Institute of British Architects has mandated that all architectural students be conversant in sustainability upon graduation. The task is for urban climatologists to engage this enthusiasm by providing course materials and easily understandable concepts and data to facilitate learning. The key message to urban climatologists is to keep reports graphical and simple, and to simply state what is prevailing and critical.