Information related to the health, chemistry, and conservation of marine ecosystems,  including coral reef health. 

marine-environment

Marine Environment

Data covering the marine environment, including fisheries, coral reef  health, ocean chemistry, and coastal zones.

oceans-seas-coasts

Oceans, Seas, & Coasts

### Overview  
  
This dataset shows the frequency and intensity of heat stress events. Heat stress events can be detected using sea surface temperature (SST), which is the water temperature close to the ocean's surface. A heat stress event occurs when the SST near coral reefs exceeds the historical baseline for that area. This dataset describes the number of heat stress events and the average period of time between them during 1985-2018 at a 5 kilometer (km) resolution. 

  
  
Stress events are defined by applying Coral Reef Watch's [Degree Heating Week (DHW) methodology] (https://coralreefwatch.noaa.gov/satellite/education/tutorial/crw24_dhw_product.php) at coral reef-containing and adjacent satellite pixel locations worldwide. The DHW attempts to capture both the level of abnormal heating and its duration: 1 DHW is equivalent to 1 week of SST 1°C above the expected summertime maximum at a given location. The three thresholds for heat stress in this dataset correspond to occurrence (DHW>0), significant coral bleaching (DHW≥4), and widespread bleaching and significant mortality (DHW≥8).

  
  
SST and its fluctuations are critical to ecosystem dynamics and health, as many marine organisms can thrive only within certain temperature ranges. In particular, research indicates that a coral reef’s “thermal history” is among the most important factors influencing its ability to withstand heat stress events. Accordingly, with support from the National Oceanic and Atmospheric Administration (NOAA) [Coral Reef Conservation Program](http://coralreef.noaa.gov/), [Coral Reef Watch (CRW)] (https://coralreefwatch.noaa.gov/satellite/index.php) developed a variety of thermal history metrics for coral reef management, initially released in July 2014. The metrics were derived from CRW's Version 3.1 [CoralTemp daily global 5 km (1/20°) satellite SST data product] (https://coralreefwatch.noaa.gov/product/5km/index_5km_sst.php), for the period 1985-2018. 

  
  
Coral reef sites that have experienced fewer heat stress events may have natural protection from exposure to conditions conducive to bleaching (e.g., strong mixing, upwelling). However, corals at those sites may also be more sensitive to heat stress, resulting in higher impacts if a stress event does occur. Alternatively, sites that have been regularly exposed to heat stress can have a reduced sensitivity, and therefore lower impact from the stress.

  
  
Coral reefs are among the most biologically rich and productive ecosystems on earth and provide valuable ecosystem benefits to millions of people in coastal areas. They are, however, widely threatened by both local threats (such as overfishing, pollution, and direct physical damage) and the global threats of ocean warming and acidification. These have already caused widespread damage to most of the world’s coral reefs, resulting in reduced areas of living coral, increased algal cover, diminished species diversity, and lower fish abundance, as well as degraded economic and social benefits to many coastal communities.
  
  
### Methodology  
  
Stress events are defined for 1985-2018 by applying CRW's Degree Heating Week (DHW) methodology at pixel locations worldwide that either contained coral reefs or were adjacent to pixels that did. SST input data were drawn from the [CoralTemp daily global 5 km satellite SST data product (Version 3.1)](https://coralreefwatch.noaa.gov/product/5km/index_5km_sst.php), which represents the nighttime ocean temperature measured at the surface. The source data for CoralTemp are a combination of the:
  
  
1. NOAA/National Environmental Satellite, Data, and Information Service (NESDIS) operational near real-time daily global 5 km Geostationary-Polar-orbiting (Geo-Polar) Blended Night-only SST Analysis;
  
  
2. NOAA/NESDIS 2002-2016 reprocessed daily global 5 km Geo-Polar Blended Night-only SST Analysis; and the
  
  
3. 1985-2002 daily global 5 km night-only SST reanalysis produced by the United Kingdom Met Office, on the Operational SST and Sea Ice Analysis (OSTIA) system.

  
  
NOAA's daily global 5 km Geostationary-Polar Blended Night-only SST Analyses (both the near real-time and reprocessed products) utilize sensors from multiple geostationary and polar-orbiting satellites to derive a global SST data field at a resolution of 5 km (1/20°). The few remaining gaps are filled using optimal interpolation through space and time.

  
  
Heat stress will build up if the temperature around corals rises and stays above the bleaching threshold (1°C above the highest summertime mean SST). The DHW is the product of the deviation above this threshold and the length of time it persists. This captures not only how far the temperature is above the threshold, but how long it has stayed above that point. Thus the DHW shows how much heat stress has accumulated in an area over the past 12 weeks. It is a running sum: as time advances one half-week (a timestep), a half-week timestep "falls off" the back end of the 12-week window.

  
  
For the full documentation, please click on the “Learn more” button.
  
  
### Additional Information  
  
Resource Watch shows only a subset of the dataset. Additional data about heat stress frequency, heat stress onset, SST variability, SST trends, climatology, and annual SST history are available from the data provider. For access to the full dataset and additional information, click on the “Learn more” button.  
  
### Visualizing the Data  
  
Our team reformatted this dataset before displaying it on Resource Watch. See the documentation on how Resource Watch retrieved the data on [Github](https://github.com/resource-watch/data-pre-processing/tree/master/ocn_008_historic_coral_bleaching_stress_frequency).  
  
### Disclaimer  
  
Excerpts of this description page were taken from the source metadata.

National Oceanic and Atmospheric Administration (NOAA)

Thermal History - Stress Frequency (1985-2018), Version 2.1

ocn-008-historical-coral-bleaching-stress-frequency-rw

ocean-watch

Ocean Watch

1985-2018 Number of Heat Stress Events

1985-2018 Number of Bleaching-Level Heat Stress Events

1985-2018 Number of Severe Heat Stress Events

1985-2018 Time between Bleaching-Level Heat Stress Events (years)

1985-2018 Time between Severe Heat Stress Events (years)

1985-2018 Time between Heat Stress Events (years)

Frequency and intensity of abnormally warm water conditions near coral reefs