Some reef regions offer years of warning for marine heat stress
A peer-reviewed modelling study assessed marine heatwave forecasts across twelve coral reef regions. In some places, the number of hot days and cumulative intensity were predictable months to years ahead, while event duration was harder to anticipate. Much of the longer-term skill came from the warming trend, with regional climate variability shaping the limits.
Science··Evening
Different warning times for different reefs
Marine heat stress can be anticipated months to years ahead in some coral reef regions, according to a peer-reviewed modelling study in Nature Communications. Researchers compared the predictability of hot-day totals, cumulative intensity and average event duration across twelve regions. The results, also reported by Scienmag, vary by location and season. Hot-day totals and cumulative intensity generally offered more predictive skill than the length of an individual event. The work concerns statistics derived from sea-surface temperature. It describes where longer-range forecasts may provide useful advance information for regional preparedness, rather than setting the starting day of a particular heatwave or a bleaching date for a specific coral community.[1], [2]
Testing five-year forecasts against the past
The team evaluated five-year hindcasts initialized annually between 1981 and 2020 using a prediction system based on Community Earth System Model version 2, a model of the coupled climate system. Hindcasts test forecasts against conditions already observed in the past. Researchers compared simulations informed by ocean observations with historical simulations without those initial conditions. Frequency in this analysis means the total number of marine-heatwave days within a season, rather than simply a count of separate episodes. A small number of long events can give a season many hot days. Average duration and cumulative intensity supply other measures of that seasonal exposure.[1]
Warming and ocean variability
Much of the multi-year forecast skill came from the long-term warming trend. Initial ocean conditions and internal climate variability influenced shorter-term skill and the contrasts among regions. The El Niño–Southern Oscillation, a coupled pattern of tropical Pacific ocean and atmospheric variability, was particularly important in the equatorial Pacific. Slower Atlantic variability also contributed to regional differences. Forecasts therefore combine influences operating on different timescales. The study used surface temperatures and did not directly resolve heat exposure in deeper coral communities. Separating the warming contribution from internal variability depends on the climate model and analytical assumptions, so the reported skill describes the tested system and regions.[1]
