Summer surface temperature of 18 Saudi cities against their surroundings: the urban heat island and where it reverses

For each city, its summer surface temperature, the temperature of the natural land around it, and the difference between them, which is the urban heat island.

With the measured built-up area, the area of the hottest tenth of the city, and the number of thermal scenes used. The clearest result is that 14 of 18 cities have a daytime surface cooler than their surroundings rather than hotter, with a mean difference of -1.0 C, a known phenomenon in hyper-arid cities.

Who it is for

Municipalities and urban planning offices, public health and climate adaptation research, greening and city-cooling programmes, and geography departments.

Method: what we add to the raw data

• Land surface temperature comes from the thermal band of summer satellite imagery, as the median of several clear scenes rather than a single one, so an unusual day cannot mislead it.
• The thermal band is acquired at a hundred-metre cell and then resampled, so measuring at sixty metres loses no real detail.
• The city is a circle around its centre with a radius approximating its built extent, and measurement inside it is restricted to built-up cells.
• The surroundings are a ring outside the city with water and cultivated land excluded: comparing a city with sea or with irrigated farms measures a land-water contrast or an irrigation effect, not a heat island. The ring widens gradually until it finds enough natural land.
• The ring is not required to be non-built by a built-up index: that index rests on high short-wave infrared reflectance with low vegetation, which also describes bare soil rather than buildings alone, and would exclude the whole desert surround of a city.
• The difference is the median city surface temperature minus the median temperature of the natural land around it.

Product details

Spatial layers

• cities_uhi — polygons, 18: Cities with their heat island difference

Tables

• D120_cities_uhi.csv — 18 rows: Cities table

Limitations

• This is surface temperature, not air temperature: asphalt in summer is tens of degrees hotter than the air above it, and these figures must not be read as what a shaded thermometer measures.
• Measurement is at the late-morning satellite overpass, and the surface heat island differs greatly from the night-time one; many desert cities are cooler than their surroundings by day and warmer by night.
• A negative difference, the city being cooler, is a known desert-city phenomenon: bare sand and rock around the city heat more than concrete, shade and irrigated areas within it.
• The city boundary here is an approximate circle, not an administrative limit, and its radius is a methodological choice; changing it changes the figure.
• Cities without enough natural land around them or enough built-up area inside them are not included.
• Scenes span several summers, so the figure is an average condition, not a measurement of one day.

FAQ

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