Streets and other built surfaces in the region absorbed and retained heat long after sunset and grew hotter over many days of persistent high temperatures.
Researchers at NASA’s Jet Propulsion Laboratory have created a series of maps showing land-surface temperatures in the Phoenix area in July 2023, when the city experienced a record-breaking run of hot weather. The images reveal the cumulative effect – overnight and across the month – of relentless daytime heating.
The data was captured during overnight hours (around 2 a.m.) on several days in July by an instrument called the Visible Infrared Imaging Radiometer Suite (VIIRS) aboard the NOAA-NASA Suomi National Polar-orbiting Partnership (Suomi NPP) satellite managed by the National Oceanic and Atmospheric Administration and NASA. The images show how built surfaces – roads, buildings, airport runways, and the like – retain heat, sometimes hovering around 100 degrees Fahrenheit (38 degrees Celsius) for hours after sunset.
From July 1 to July 19, the built surfaces in the maps grew progressively hotter, likely the combined effect of the heat wave intensifying and the cumulative heating of those human-made structures. Due to their high heat capacity, these surfaces didn’t fully cool overnight before the onset of the next day’s heat, said Glynn Hulley, the JPL climate scientist who produced the series.
Read more at NASA
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