NOAA/NESDIS Degree Heating Weeks

Degree Heating Weeks (DHWs) are an experimental product designed to indicate the length of time that coral reefs experience thermal stress. One DHW is equivalent to one week of sea surface temperatures one degree Celsius warmer than the expected summer-time maximum. Two DHWs are equivalent to two weeks at one degree above the expected summertime maximum OR one week of two degrees above the expected summertime maximum. These charts (produced biweekly at a 50km resolution) are being used to determine the amount of accumulated thermal stress that results in bleaching. We recognize that a single stress parameter such as thermal stress may not have the ability to force bleaching events in some areas without other factors (low winds, high solar irradiance, etc.) simultaneously amplifying the thermal stress. In an effort to formulate the full suite of stressors acting in concert to force bleaching, and their thresholds for particular areas, ReefBase has implemented a coral reef bleaching report form for your scientific input.

Caribbean/Central America Region:

Western Hemisphere:

Eastern Hemisphere:

Please credit NOAA/NESDIS if you wish to use these images. Also available are images with a black background (rather than white).

Coral Bleaching Indices for 24 sites around the world are available. These indices are derived from the Degree Heating Weeks chart.

See the NOAA/NESDIS HotSpot pages for more information regarding coral bleaching.