[Coral-List] The Evolution of HotSpots

[Mark Eakin]

In a recent posting, Tom Goreau raised the issue that the NOAA coral  
bleaching HotSpots are a short-term measure and differs from the  
concept as he originally conceived.  He is correct that our products  
have evolved through time and are no longer the same as the “hotspot”  
concept that he published with colleagues over a decade ago.  As Tom  
notes the early “hotspot” product was developed as an analysis of the  
monthly SST products that were available at the time.

The data from which Tom and colleagues developed the original  
“hotspots” were, in essence, blended products that used some  
satellite data but mostly in situ data to construct hand-drawn  
monthly fields.  This analysis was not available until some weeks  
after a month had concluded and used input data that varied from  
month to month.  As satellite data availability improved and Al  
Strong worked with Tom, students from the US Naval Academy, and other  
colleagues, a new set of products evolved.  These were based on daily  
satellite data of known quality and origin and were available much  
more rapidly than the old monthly data fields.  The NOAA HotSpot data  
developed as twice-weekly products (see Strong et al. 1997 and its  
references to the development from the original Goreau approach) that  
provided 3 and 4 day average anomalies above the maximum monthly mean  
in a timely manner.  It was only then that the product moved from  
being an interesting scientific product that was useful in  
understanding bleaching events in hindsight, to a product that  
scientists and managers could use to understand events that were  
taking place on their reefs in near-real-time.

However, the short-term nature of the NOAA HotSpot product left a  
need to understand the thermal stress in a way that captured both the  
long-term accumulation of stress and delivered a product in near-real- 
time.  This led to the birth of the Degree Heating Weeks, an  
accumulation of NOAA HotSpots over 12 weeks.  This product has been  
almost 100% successful in identifying conditions that result in  
bleaching.  It is a bit conservative, as some bleaching events occur  
below the Bleaching Alert Level 1 (4-8 Degree Heating Weeks).   
However, except for problems that we have recently identified in the  
climatology near Oman, all of our distributed reports of stress that  
should lead to bleaching (Alert Level 1 or higher) have been verified  
by field observations.  Our Bleaching Watches and Bleaching Warnings  
are indications that water temperatures have reached threshold levels  
and that there is a need to be on the lookout for bleaching in the  
field.

In the late 1990s, NOAA saw the need for a near-real-time monitoring  
product that could alert managers and scientists of the potential of  
bleaching.  NOAA's Coral Reef Watch is a vital program that works to  
deliver those needed products.  We stand behind the need for such a  
product suite and continue to work with reef managers to develop new  
products to improve our services.

By looking at our methodology page, our publications, and their  
references, one can find trace the evolution of the product from  
Tom's original construct to the product suite that we now provide.   
The field has probably matured enough that it is time to write a  
retrospective article on the history and evolution from Tom's  
“hotspots” to the NOAA HotSpot and NOAA Degree Heating Week products  
and our future directions.

Cheers,
Mark

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------------------------
C. Mark Eakin, Ph.D.
Coordinator, NOAA Coral Reef Watch
National Oceanic and Atmospheric Administration
Center for Satellite Applications and Research
Satellite Oceanography & Climate Division
e-mail: mark.eakin at noaa.gov
url: coralreefwatch.noaa.gov

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