Surviving in large, high–density cities is becoming increasingly challenging, especially during the hot summer months.
Urban materials, such as concrete and asphalt, absorb and retain heat, while narrow streets and tall buildings create “urban canyons” that trap solar radiation and block airflow. The lack of vegetation compounds the problem by reducing shade and eliminating natural cooling.
But how can we monitor and measure urban heat? Mallon colleague Anastasiia Khil has created the following maps that show how Earth Observation technologies can help us better understand and monitor urban heat islands.
How Can Earth Observation Address Urban Heat?
Satellites such as Landsat, Sentinel–3, and MODIS (Moderate Resolution Imaging Spectroradiometer) measure thermal infrared radiation, enabling the detection of Land Surface Temperature (LST) in both urban and rural areas. Unlike air or ambient temperature (measured by weather stations), LST reflects the heat emitted from the Earth’s surface—buildings, soil, vegetation, and more.
Among these, MODIS offers daily LST observations at a 1 km spatial resolution, making it well–suited for regional–scale analysis. Operating aboard the Terra (launched in 1999) and Aqua (2002) satellites, MODIS can deliver up to four measurements per day. Despite being primarily an ocean sensor, MODIS’s high revisit frequency makes it valuable for tracking temporal trends, particularly for studying Urban Heat Islands (UHIs), even if it provides coarser resolution than land–focused missions like Landsat.
Monitoring Urban Heat: 20 Years of Data
This blog focuses on Dublin and London—two major European cities with similar climates but differing urban densities. For the analysis, we used MODIS Aqua data at 13:30 local time for daytime and 01:30 for night time. We examined the average LST and air temperature from April 15 to May 15 annually over a 22–year period.
The chart above shows that while LST and air temperature follow similar trends, they differ in absolute values. Notably, daytime LST is typically higher than air temperature due to the efficient heat absorption of urban surfaces. At night, LST drops more rapidly as surfaces release the stored heat, sometimes falling below the ambient air temperature.
London consistently records higher urban temperatures than Dublin, which is attributed to its denser built environment, larger population, and higher energy consumption. Between 2003 and 2025, both cities saw average air temperature increases of up to 2°C during this period, with LST trends closely mirroring this rise.
Mapping Urban Heat Islands
The maps below depict day and night LST across Dublin and London. London exhibits consistently higher LST values, highlighted in deeper red tones during the day and warmer greens at night, reflecting more intense urbanisation.
Green spaces provide noticeable cooling effects, especially along city perimeters. For example, Phoenix Park in Dublin (707 hectares) appears cooler, even at a regional scale, with an average LST of around 18°C, visible in the map’s upper left.
Water bodies also contribute to localised cooling. Coastal areas around Dublin remain cooler during the day and warmer at night, demonstrating the water’s moderating influence. Similar effects are observed near the Liffey in Dublin and the Thames in London.
During the day, the urban core of each city appears as saturated red zones—hotspots associated with dense construction and minimal vegetation. At night, cooler areas spread out, marked in green. These Urban Heat Islands align with residential and industrial zones.
Conclusion
Satellite–derived LST data provides clear evidence of growing urban heat. Both Dublin and London exhibit Urban Heat Islands, visible in stark colour contrasts—vivid reds in the daytime and warmer greens at night. These hotspots correlate with built–up zones, areas of industrial activity, and regions lacking vegetation.
What Can Be Done to Cool Our Cities?
To mitigate urban heat and enhance liveability, cities can adopt the following measures:
- Expand green infrastructure: urban forests, green roofs, vertical gardens
- Use reflective or cool roofing materials: white membranes, reflective–coated metal roofs
- Implement climate–sensitive urban planning: more open spaces, integrated water bodies, better airflow
- Reduce car dependency and transition to clean energy sources
As EO data continues to improve, it offers powerful tools for urban planners, policymakers, and citizens alike to better understand, monitor, and respond to rising urban temperatures.
Further Information
For further information about the methods used to produce the maps above or to discuss your Earth Observation requirements, contact us below.
