UHI RISK ASSESMENT GLOSSARY

UHI Glossary

Adaptive capacity:

The ability of individuals to adjust to climate variability and extremes in order to mitigate potential impacts and cope with the consequences. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9859186/). 

Albedo coefficient:

Albedo (sometimes referred to as ‘reflection coefficient’) is a measure of how reflective a surface is. The term is derived from the Latin albus meaning ‘white’ and is either determined by a value between 0 and 1 or a percentage value. The more reflective a surface is the higher the albedo value. ((https://www.rff.org/publications/explainers/urban-heat-islands-101/)

Anthropogenic heat:

In cities, people drive cars, run air conditioning units, and operate buildings and industrial facilities in close contact with each other—activities that generate waste heat that increases local temperatures. (https://www.metoffice.gov.uk/weather/learn-about/weather/atmosphere/albedo#:~:text=Albedo%20(sometimes%20referred%20to%20as,the%20higher%20the%20albedo%20value)

Atmospheric heat islands: 

These heat islands form as a result of warmer air in urban areas compared to cooler air in outlying areas. Atmospheric heat islands vary much less in intensity than surface heat islands.

Building coverage ratio (BCR):

The proportion of a parcel covered by buildings, measured as a ratio of the site occupied by the building and the site area (plot/parcel or larger area). (https://urbanana.su/glossary/building-coverage-ratio-bcr/)

Buildings volume ratio:

The area occupied with the volume of all buildings in a site area.

Evaporation:

Evaporation is the process that changes liquid water to gaseous water (water vapor).

Evapotranspiration:

The process by which water is transferred from the land to the atmosphere by evaporation from the soil and other surfaces and by transpiration from plants.

Floor area ratio (FAR):

A measure describing how much land is covered by a building/buildings, calculated as a ratio of the total floor area (sum of all floors) of land covered by building and the entire area upon which the building /buildings stand. (https://www.planetizen.com/definition/floor-area-ratio).

Fragility refers to the susceptibility of individuals with certain health conditions that make them more prone to suffering from extreme climate events.

Green roofs are layers of vegetation planted on rooftops, designed to improve energy efficiency, manage stormwater, and enhance urban biodiversity. They connect with sustainable development by promoting eco-friendly architecture, reducing the urban heat island effect, and providing additional green spaces in cities. By incorporating living plants into building designs, green roofs contribute to healthier environments and more sustainable urban living. (https://library.fiveable.me/key-terms/ap-hug/green-roofs)

Heat generated from human activities (anthropogenic heat):

Vehicles, air-conditioning units, buildings, and industrial facilities all emit heat into the urban environment. These sources of human-generated, or anthropogenic, waste heat can contribute to heat island effects. (https://www.epa.gov/heatislands/what-are-heat-islands)

Impermeable surfaces:

An ability of surfaces that don´t allow water or any other fluid to penetrate or pass through it, forcing it to run off. (https://www.corrosionpedia.com/definition/4667/impermeable-surface; Permeable Vs. Impermeable Surfaces | Cooperative Extension | University of Delaware)

Land use:

The use of land for the needs of human activities like agricultural, residential, industrial, mixed use, recreational and other.

Micro urban heat islands:

They refer to urban hot spots as poorly vegetated parking lots, non-reflective roofs and asphalt roads. Micro urban heat islands are strongly affected by micro climate factors, therefore remotely sensed data are more suitable than atmospheric data for identifying heat spots. (https://www.urbanheatislands.com/heat-island-types)

Non-residential suburban area:

Area with shopping centers, malls and industrial activity, wide streets and very little vegetation.

Permeability of surfaces:

Ability of urban surfaces to pass water through into the soil. (Permeable Vs. Impermeable Surfaces | Cooperative Extension | University of Delaware.

Residential suburban area:

Sparse area intended almost exclusively for households.

Solar radiation:

The electromagnetic energy emitted by the sun that reaches Earth. It affects Earth’s climate and temperature through absorption and reflection processes in the atmosphere. (https://weathermonths.com/solar-radiation/)

Social vulnerability refers to the varying degrees of susceptibility and capacity to cope with the impacts of high temperatures within urban environments, influenced by social, economic, and demographic factors. Certain groups or communities within a city may be more at risk from heat-related stresses or might have fewer coping capacities due to factors such as age and health, limited access to cooling resources and green spaces, poor housing conditions exacerbating the effects of urban heat, outdoor jobs with high heat exposure social isolation and lacking support systems to cope with extreme heat events.

Street canyon:

A ‘Street Canyon’ is defined as a confined urban space surrounded by buildings on both sides of a street, where natural air ventilation is limited, leading to the accumulation of pollutants from vehicle emissions and other sources, posing health risks to pedestrians and residents. (https://www.sciencedirect.com/topics/earth-and-planetary-sciences/street-canyon)

Street canyon aspect ratio:

The size of the open space in the street, measured as a ratio of the average building height of the street and the street width. (https://www.sciencedirect.com/topics/earth-and-planetary-sciences/street-canyon)

Surface heat islands:

These heat islands form because urban surfaces such as roadways and rooftops absorb and emit heat to a greater extent than most natural surfaces. (https://www.epa.gov/heatislands/learn-about-heat-islands)

Surface temperatures represent heat energy given off by the land, buildings, and other surfaces. Technologies that measure temperatures of surfaces, such as instruments mounted on satellites and airplanes, can provide better geographic coverage than those used for recording air temperatures. They can reveal temperature differences at very fine scales: for example, between roofs, pavements, and grassy areas. (https://www.epa.gov/heatislands/measuring-heat-islands)

Temperature thresholds:

Temperature thresholds at which materials and equipment pose a risk of exacerbating UHI effects.

Surface heat islands:

Transpiration:

The process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers. 

Tree canopy:

The upper level of trees consisting of branches and leaves, which can create shade on the land, measured as a tree canopy coverage. (https://www.smallspacegardeningbasics.com/what-is-a-tree-canopy/)

Tree canopy coverage:

The proportion of the area covered by the vertical projection of tree crowns.

Urban built-up area:

“Built-up area” is defined as the presence of buildings (roofed structures). This definition largely excludes other parts of urban environments or human footprint such as paved surfaces (roads, parking lots), commercial and industrial sites (ports, landfills, quarries, runways) and urban green spaces (parks, gardens). (https://www.oecd-ilibrary.org/environment/built-up-area/indicator/english_7c06b772-en)

Urban climate:

Climatic conditions in urbanised areas.

Urban geometry:

The dimensions and spacing of buildings within a city influence wind flow and urban materials’ ability to absorb and release solar energy. In heavily developed areas, surfaces and structures obstructed by neighboring buildings become large thermal masses that cannot release their heat readily. Cities with many narrow streets and tall buildings become urban canyons, which can block natural wind flow that would bring cooling effects. (https://www.epa.gov/heatislands/what-are-heat-islands)

Urban haze:

The haze of air pollution that hangs over many cities can act as a miniature greenhouse layer, preventing outgoing thermal radiation (heat) from escaping from urban areas. (https://scied.ucar.edu/learning-zone/climate-change-impacts/urban-heat-islands)

Urban heat sink:

Also called negative heat island. It is the expression of a city colder than their countrysides. There are few references about this phenomenon. Heat sinks have been observed in cities with temperate, tropical, semi-arid and arid climates, and mainly during the mornings. (https://www.urbanheatislands.com/heat-island-types)

Urban morphology:

Spatial patterns of urban landscapes composed by different urban elements; study of the formation and transformation of cities, towns, and villages over time, their urban patterns and physical characteristics. (https://www.oxfordbibliographies.com/display/document/obo-9780190922481/obo-9780190922481-0004.xml)

UHI risk assessment provides information about the existing weaknesses of a natural or a socioeconomic system and the plausible causes of the weaknesses. ((https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9859186/)

Urban surfaces:

Human-made building materials such as pavement and concrete reflect less sunlight and absorb more heat than natural surfaces. 