Degree Heating Weeks
Also known as: DHW, Thermal Stress Index
Degree Heating Weeks (DHW) is a thermal stress metric that quantifies accumulated heat exposure above a coral bleaching threshold, computed from satellite sea surface temperature data. Developed by NOAA's Coral Reef Watch program in 2003, DHW provides a standardized index for predicting and monitoring coral bleaching stress globally. The metric combines intensity and duration of thermal anomalies to estimate cumulative physiological stress on coral colonies.
Read the full method
Sign in with a free account to read this section.
Method map
The neighbourhood of related methods — select a node to explore.
When to use it
DHW is the standard metric for tropical and subtropical coral reef bleaching risk assessment. Use it when monitoring coral thermal stress in real-time or when retrospectively analyzing historical bleaching events. DHW is particularly valuable during the warm season (summer-fall in most regions) when thermal stress is highest. The metric is less applicable to non-coral marine ecosystems or to organisms with different thermal tolerance mechanisms.
Strengths & limitations
- Universally applicable across coral reef regions; a single DHW threshold (nominally 1°C-week) has shown predictive skill for bleaching occurrence globally
- Based on satellite data with global coverage and no dependence on in situ buoy networks
- Simple, transparent calculation that can be reproduced independently and understood by non-specialists
- Real-time operational forecasts provide early warning weeks to months before bleaching peak, allowing proactive management
- Assumes all corals respond identically to thermal stress; ignores genetic variation, acclimatization, and symbiont-dependent bleaching thresholds
- Neglects other stressors (light stress, disease, freshwater influx, ocean acidification) that interact with thermal stress to exacerbate bleaching
- Satellite-derived SST has uncertainty (±0.5-1°C); this error can be significant near the bleaching threshold
- DHW does not account for diel (daily) temperature fluctuations or subsurface temperature structures that corals may exploit
Frequently asked
Why is a 12-week window used for DHW, not a longer or shorter period?
The 12-week window reflects the typical timescale of coral bleaching onset and progression. Shorter windows miss the cumulative stress effect; longer windows include historical anomalies that may be physiologically irrelevant. The 12-week window was empirically validated against observed bleaching events globally.
Can DHW predict which individual reefs will bleach?
DHW is a regional-scale metric (typically 5 km pixels); it indicates bleaching risk across a broad area but cannot resolve fine-scale spatial variation in local SST, water depth, or coral genotype. Site-specific bleaching prediction requires additional local data (e.g., buoy SST, species surveys, turbidity).
What DHW value indicates severe bleaching?
Empirical calibration suggests DHW 4-7°C-weeks indicates moderate bleaching (50% of corals affected), while DHW >8°C-weeks indicates severe bleaching (>70% of corals affected). However, this relationship varies by region and coral community composition; some regions bleach more readily at lower DHW values.
Sources
- Liu, G., Strong, A. E., & Skirving, W. (2003). Remote sensing of sea surface temperatures during 2002 Great Barrier Reef coral bleaching. EOS Transactions, 84(15), 137-141. link ↗
- Strong, A. E., Liu, G., Meyer, V., et al. (2016). Integrating thermal habitat monitoring and coral bleaching forecasting. Coral Reefs, 35(1), 1-7. link ↗
How to cite this page
ScholarGate. (2026, June 3). Degree Heating Weeks. ScholarGate. https://scholargate.app/en/oceanography/degree-heating-weeks
Which method?
Set this method beside its closest kin and read them side by side — the library lays the books on the table; the choice is yours.
- Drifter Lagrangian AnalysisOceanography↔ compare
- Hydrothermal Plume MappingOceanography↔ compare
- Ocean Color Chlorophyll-aOceanography↔ compare