Heat Risk Index Athens, Greece
Abstract
This study presents a methodology for mapping heat risk in urban areas, with a focus on densely populated regions like Athens. The primary goal is to calculate a Heat Risk Index (HRI) and visualize it on a map, providing valuable insights for urban planners and policymakers. First, we retrieve Landsat 8 and Sentinel-2 imagery from Living Atlas, which captures land surface temperature and NDVI data for Athens during the summer of 2023, along with population data from WorldPop. These images are then processed in ArcGIS Pro as raster layers, normalized, and combined to derive the Heat Risk Index with a spatial resolution of 20x20 meters. The method not only identifies areas with increased heat risk but also pinpoints heat-resilient zones, guiding strategic interventions like tree planting or the use of cool materials. Specific areas in Athens susceptible to heat risks are identified in zones with high urban density, proximity to major highways, and limited tree coverage. The research emphasizes the significance of strategic interventions, such as green spaces, to mitigate heat risk and underscores the need for innovative solutions to promote public health and well-being through a sustainable urban environment.
Introduction
Urban Heat Islands
Urban Heat Island
An urban heat island (UHI) refers to the phenomenon where urban areas experience higher temperatures compared to their surrounding rural areas. This temperature difference is primarily due to human activities and the dense built environment in citites.
Suburban Areas
Dense vegetation provides shade and moisture that help reduce temperatures.
Industrial Zones
Heat from industrial operations and increased vehicle traffic cause increased temperatures as a consequence of higher GHG emissions.
Surface Temperatures
Synthetic building materials, such as asphalt and cement, reflect less sunlight and absorb more heat. They heat up quickly during the day and slowly release heat at night, causing higher temperatures 24 hours a day.
Human Activities
Traffic, increased use of air-conditioning and industrial areas are most seen in urban areas.
These activities release GHG, which further raise temperatures. When these activities are all concentrated in small areas, the UHI effect is even more intense.
Greenhouse effect
Urban settings usually contain higher concentrations of pollutants and have a higher water vapour content. Combined with warmer air, these factors trap and amplify heat in cities.
Current Situation in Athens
Athens, Greece: Profile
- Athens Metropolitan Area Population: 3.622.246 (as of 2021)
- Area: 574,7 km^2
- Municipalities: 43
Temperatures
The 2023 heatwave in Athens, also known as "Cleon", was a historical milestone:
- the average maximum temperature reached 37,1°C, the highest recorded since 1863.
- the highest temperature reached 42,8° C.
- Had a duration of 15 days, breaking all records (Kathimerini, 2023).
The same source states that the highest minimum (night) temperature was 30.8°C, while the record of 31.6°C was observed in August 2021, when a maximum absolute temperature of 43.9°C was recorded.
Temperatures
The summer of 2021 was:
- The 5th warmest summer regarding maximum temperatures.
- The 3rd hottest summer, following 2012 and 2007 in terms of daily temperatures.
- The 2nd warmest summer, following 2012 regarding minimum daily temperatures.
Health effects of heat waves
Heat waves and extended high temperature periods cause significant public health problems that cannot be ignored.
Health effects of heat waves
Studies have shown that mortality in Athens in recent years has increased by about 20% during heat waves, while between 28/7-6/8/2021, in combination with the fire in Varybombi, it increased by 80% (Kathimerini 2023).
Death rates rose by 97% in Athens during the 1987 heatwave and a large part were due to cardiovascular problems. These symptoms usually occur during the first few days of a heatwave, when the body is not yet adjusted to the heat. Acclimatisation takes 7 to 14 days of exposure.
Purpose of Study
Specify high risk areas
Using satellite imagery and population data of Athens, we try to visualize which areas require immediate attention and intervention against extremely high temperatures, and distinguish any patterns.
Identify heat-resilient zones
How and to what extent do green spaces protect areas with high population density and high building density?
Incentivize policy makers
This study aims to provide a guideline for the responsible authorities to take effective mitigation actions.
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Layers - Heat Risk Index
Vegetation Index and Soil Temperature Index
Tree Canopy - NDVI
From the Sentinel satellite system we used the imagery to calculate the index Normalized Difference Vegetation Index (NDVI).
NDVI is used to quantify vegetation greenness and is useful for understanding vegetation density and assessing changes in plant health. In this study, it was used to estimate the locations of vegetation in Athens.
Sentinel 2 offers spatial resolution (10 meters) and a frequent recording period (5 days)
The percentage of trees in Athens is 11%, while the EU average is 30%.
Land Surface Temperature
From the Landsat 8 satellite system, we used the imagery to calculate the Land Surface Temperature (LST) index.
The LST serves as a valuable metric for comprehending the average temperature prevailing in the study area over the specified period.
Investing in cool materials in neighborhoods and urban green spaces can reduce temperatures by 5 degrees in the summer months.
Landsat 8 is the preferred choice for surface temperature assessments due to its Thermal Infrared Sensor (TIRS), which reliably captures long-wave thermal radiation with a resolution of 100 meters.
High surface temperatures are observed in areas with :
- ,
- &
Population Density
Population data from the WorldPop project database.
WorldPop is a research project based in the Department of Geography and Environmental Sciences at the University of Southampton.
Half of the population of Greece lives in just 4.3% of the territory.
Municipality - Region | Population |
|---|---|
Attica | 3.814.064 |
Municipality of Athens | 643.452 |
Galatsi | 57.909 |
Vyronas | 59.134 |
Kallithea | 97.616 |
Zografou | 69.874 |
Municipality - Region | Population |
|---|---|
Attica | 3.814.064 |
Municipality of Athens | 643.452 |
Galatsi | 57.909 |
Vyronas | 59.134 |
Kallithea | 97.616 |
Zografou | 69.874 |
Municipality - Region | Population |
|---|---|
Attica | 3.814.064 |
Municipality of Athens | 643.452 |
Galatsi | 57.909 |
Vyronas | 59.134 |
Kallithea | 97.616 |
Zografou | 69.874 |
Municipality - Region | Population |
|---|---|
Attica | 3.814.064 |
Municipality of Athens | 643.452 |
Δήμος Γαλατσίου | 57.909 |
Vyronas | 59.134 |
Kallithea | 97.616 |
Zografou | 69.874 |
Methodology Workflow
Methodology Workflow
Heat Risk Index
Heat Risk Index Combination
HRI visualization for the Attica basin
Heat Risk Index 2023 Athens
Index - Discussion
Areas requiring immediate intervention
In Piraeus, HRIs greater than 3 were estimated near motorways such as Petrou Ralli, Lambraki Gregoriou, Tzavella and Pireos
and in many zones of Nikaia and Korydallos.
In Western Athens, high HRI are observed near Kifissos Avenue and in smaller areas of Peristeri, Thivon Street, Petroupolis and Nea Ionia.
High HRI are found in the areas of Patissia, Galatsi, Sepolia, Metaxourgeio, Omonia and mainly near the streets of Athinon and Patision (28th October)
High HRI also occur in areas surrounding major city highways, where higher surface temperatures and very low tree coverage are observed.
In the business area, high HRI values are observed within the boundaries of Stadiou and Solonos up to Omonia
Several blocks in the central part of Athens, in the areas of Neos Kosmos, Pagrati and Kaisariani on Ymittos and Filolaou streets, as well as parts of Vyronas and the centre of Zografou also have a high thermal risk.
In the South Zone of Athens, similar HRI values appear in the blocks of Kallithea and Nea Smyrni, bordering Sygrou Avenue or Venizelou.
Areas with low thermal risk
Comparison between 2021 and 2023
Comparison of HRI between 2021 and 2023. The left pane shows the index for 2023 and the right pane shows the index for 2021.
Recommended actions
Identification of Vulnerable Areas
Design of Mitigation Measures
More detailed demographics for identifying vulnerable groups
Rule 3 - 30 -300
- 3 means that each apartment building should have a view of at least three trees.
- 30 refers to the natural shading of every neighborhood in the city. We need 30% of streets, squares, sidewalks, school yards and other public buildings to have natural shade.
- The 300 target refers to the maximum distance that any part of the city should have from a green space of at least one acre, for Athens.
Access the survey data by clicking below
or via the following qr code
Access to survey data
