Daily Coral Bleaching Heat Stress Alert Area
Healthy coral reefs provide a home for millions of aquatic species and numerous ecosystemic services. Yet they are severely threatened. When stressed, corals expel the symbiotic algae living in their tissues and become white (bleached) and vulnerable. The NOAA Coral Reef Watch daily global 5km satellite coral Bleaching Alert Area (7-day maximum) is a composite product that summarizes the current Degree Heating Week (a cumulative measurement of both intensity and duration of heat stress) and Coral Bleaching HotSpot (occurrence and magnitude of instantaneous heat stress) values. At a glance, this layer outlines the current locations, coverage, and potential risk level of coral bleaching heat stress.
Recommendations on citation available at: https://coralreefwatch.noaa.gov/satellite/docs/recommendations_crw_cita…
Related tool or portal
Date or time period of observation
Frequency of update
Note that in the Bleaching Alert Area (7-day maximum) composite product, locations with a status of No Stress or Bleaching Watch, for a 7-day time period, may still have been exposed to recent heat stress, including in the days immediately preceding the 7-day period under evaluation. The reason is that the Bleaching Alert Area (7-day maximum) composite product classifies the heat stress condition for a specified 7-day period only -- and that heat stress level is determined by the seven, most-recent daily value pairs of CRW's daily global 5km Coral Bleaching HotSpot and DHW. So if, during the specified 7-day period being evaluated, the seven Coral Bleaching HotSpot values (within the seven daily pairs of Coral Bleaching HotSpot/DHW) were all zero, this would indicate the absence of active heat stress. For that reason, a No Stress level would be assigned; and any heat stress experienced during the 11 weeks preceding the 7-day period would not be examined, as corals should be in a recovery state. If, during the specified 7-day period being evaluated, any of the seven Coral Bleaching HotSpot values (within the seven daily Coral Bleaching HotSpot/DHW pairs) were greater than zero, but below the bleaching threshold for accumulating DHWs, this would indicate that there is currently insufficient heat stress to actively cause or worsen visible bleaching. For this reason, none of the seven daily DHW values (within the seven daily Coral Bleaching HotSpot/DHW pairs) would be examined; a Bleaching Watch level would be assigned; and any recently-accumulated DHWs greater than zero, that occurred within the 11 weeks preceding the 7-day period, would not be used to determine the current Bleaching Alert Area heat stress level. With that said, if on any future day, the Coral Bleaching HotSpot resurrected, and was greater than the threshold for accumulating DHWs, then recent heat stress exposure during the entire past 12 weeks (84 days) would be evaluated. This means all daily Coral Bleaching HotSpot values that exceeded the bleaching threshold during the past 12 weeks would be accumulated to calculate the DHWs and determine the Bleaching Alert Area (7-day maximum) composite product heat stress level. As a result, a future heat stress level could jump from No Stress or Bleaching Watch to any of the higher levels, as the calculation again would be dependent on recent heat stress exposure during the last 12 weeks. This situation also applies to the single-day Bleaching Alert Area product. As noted previously, the timing of the peak bleaching season each year varies among ocean basins and hemispheres, but it is generally during the local summertime. Thus, the peak season is July-September for the northern Atlantic and Pacific Oceans, and January-March for the southern Atlantic and Pacific. The peak is April-June for the northern Indian Ocean and January-April for the southern Indian Ocean.
Select for mapping