The energetic basis of the urban heat island

Progress in urban climatology over the two decades since the first publication of the International Journal of Climatology is reviewed. It is emphasized that urban climatology during this period has benefited from conceptual advances made in microclimatology and boundary-layer climatology in general. The role of scale, heterogeneity, dynamic source areas for turbulent fluxes and the complexity introduced by the roughness sublayer over the tall, rigid roughness elements of cities is described. The diversity of urban heat islands, depending on the medium sensed and the sensing technique, is explained. The review focuses on two areas within urban climatology. First, it assesses advances in the study of selected urban climatic processes relating to urban atmospheric turbulence (including surface roughness) and exchange processes for energy and water, at scales of consideration ranging from individual facets of the urban environment, through streets and city blocks to neighbourhoods. Second, it explores the literature on the urban temperature field. The state of knowledge about urban heat islands around 1980 is described and work since then is assessed in terms of similarities to and contrasts with that situation. Finally, the main advances are summarized and recommendations for urban climate work in the future are made. Copyright © 2003 Royal Meteorological Society.

/pdf/two-decades-of-urban-climate-research-a-review-of-turbulence-12p43b6trj.pdf

Two decades of urban climate research: a review of turbulence, exchanges of energy and water, and the urban heat island

An urban surface scheme for atmospheric mesoscale models is presented. A generaliz- ation of local canyon geometry is defined instead of the usual bare soil formulation currently used to represent cities in atmospheric models. This allows refinement of the radiative budgets as well as momentum, turbulent heat and ground fluxes. The scheme is aimed to be as general as possible, in order to represent any city in the world, for any time or weather condition (heat island cooling by night, urban wake, water evaporation after rainfall and snow effects). Two main parts of the scheme are validated against published data. Firstly, it is shown that the evolution of the model-predicted fluxes during a night with calm winds is satisfactory, considering both the longwave budget and the surface temperatures. Secondly, the original shortwave scheme is tested off-line and compared to the effective albedo of a canyon scale model. These two validations show that the radiative energy input to the urban surface model is realistic. Sensitivity tests of the model are performed for one-year simulation periods, for both oceanic and continental climates. The scheme has the ability to retrieve, without ad hoc assumptions, the diurnal hysteresis between the turbulent heat flux and ground heat flux. It reproduces the damping of the daytime turbulent heat flux by the heat storage flux observed in city centres. The latent heat flux is negligible on average, but can be large when short time scales are considered (especially after rainfall). It also suggests that in densely built areas, domestic heating can overwhelm the net radiation, and supply a continuous turbulent heat flux towards the atmosphere. This becomes very important in winter for continental climates. Finally, a comparison with a vegetation scheme shows that the suburban environment can be represented with a bare soil formulation for large temporal or spatial averages (typical of global climatic studies), but that a surface scheme dedicated to the urban surface is necessary when smaller scales are considered: town meteorological forecasts, mesoscale or local studies.

A physically-based scheme for the urban energy budget in atmospheric models

Urban Heat Island (UHI) is considered as one of the major problems in the 21st century posed to human beings as a result of urbanization and industrialization of human civilization. The large amount of heat generated from urban structures, as they consume and re-radiate solar radiations, and from the anthropogenic heat sources are the main causes of UHI. The two heat sources increase the temperatures of an urban area as compared to its surroundings, which is known as Urban Heat Island Intensity (UHII). The problem is even worse in cities or metropolises with large population and extensive economic activities. The estimated three billion people living in the urban areas in the world are directly exposed to the problem, which will be increased significantly in the near future. Due to the severity of the problem, vast research effort has been dedicated and a wide range of literature is available for the subject. The literature available in this area includes the latest research approaches, concepts, methodologies, latest investigation tools and mitigation measures. This study was carried out to review and summarize this research area through an investigation of the most important feature of UHI. It was concluded that the heat re-radiated by the urban structures plays the most important role which should be investigated in details to study urban heating especially the UHI. It was also concluded that the future research should be focused on design and planning parameters for reducing the effects of urban heat island and ultimately living in a better environment.

http://www.jesc.ac.cn/jesc_en/ch/reader/create_pdf.aspx?file_no=2008200119

A review on the generation, determination and mitigation of Urban Heat Island

Direct evidence demonstrates that urban and industrial air pollution can completely shut off precipitation from clouds that have temperatures at their tops of about –10°C over large areas. Satellite data reveal plumes of reduced cloud particle size and suppressed precipitation originating from major urban areas and from industrial facilities such as power plants. Measurements obtained by the Tropical Rainfall Measuring Mission satellite reveal that both cloud droplet coalescence and ice precipitation formation are inhibited in polluted clouds.

https://science.sciencemag.org/content/sci/287/5459/1793.full.pdf

Suppression of rain and snow by urban and industrial air pollution

http://www.met.reading.ac.uk/micromet/publications/AE_MexicoCity.pdf

The energy balance of central Mexico City during the dry season

https://archive-mirage-mex.acom.ucar.edu/Private/Literature/1997Jauregui.pdf

Heat island development in Mexico City

Urban effects on convective precipitation in Mexico city

The potential for damage from hurricanes landfalling in Mexico is assessed. During the 1951-2000 period, Pacific hurricane hits were more frequent on coastal areas of the northwest of the country (e.g., Sinaloa and the southern half of Baja California Peninsula) as well as in southern Mexico (Michoacan). On the Atlantic side, the Yucatan Peninsula and the northern state of Tamaulipas were the most exposed to these storms. The hurricane season reaches maximum activity in September for both the Atlantic and Pacific coasts of the country. During the 50 year period, five intense hurricanes (category 5) made landfall on the Gulf/Caribbean coasts, while only one such intense hurricane made a land hit on the Pacific side. While hurricanes affecting Pacific coasts show a marked increase during the last decade, those of the Atlantic side exhibit a marked de-crease since the 1970s. However, when considering the frequency of landfalling tropical storms and hurricanes impacting on both littorals of the country, their numbers have considerably increased during the 1990s.

/pdf/climatology-of-landfalling-hurricanes-and-tropical-storms-in-32sqcexhp6.pdf

Ernesto Jáuregui

Papers

The energy balance of central Mexico City during the dry season

Heat island development in Mexico City

Urban effects on convective precipitation in Mexico city

Climatology of landfalling hurricanes and tropical storms in Mexico

The surface energy balance in Mexico City