Identifying an Evaporative Thermal Refugium for the Preservation of Coral Reefs in a Warming World—The Gulf of Eilat (Aqaba).

Coral bleaching events are more frequent and severe as global temperatures rise. However, analysis of the surface energy fluxes that substantially affect the thermoregulation of shallow reef environments is rare. Previous work on evaporative cooling in a humid reef environment led to the hypothesis that in proximity to desert regions, drier air enhances evaporative cooling of water overlying coral reefs, reducing the risk of extreme high‐water temperatures. Eddy Covariance measurements made over a shallow desert fringing coral reef in the Gulf of Eilat (Israel) during summer measured evaporation of 10.3 mm d−1 which is maintaining water temperature much lower than the overlying air temperature. In addition, measurements of the most severe marine heatwave that was ever documented in the region are presented as a case study for future reference to the processes that lead to and proceed a marine heatwave, which is induced by synoptic scale events that cause a ∼50% reduction in evaporation rate. Results are compared to similar measurements from a tropical coral reef, where a lower evaporation rate suppressed by higher humidity is unable to offset the heating of water overlying the reef. We conclude that evaporative cooling is a key mechanism protecting coral reefs located in deserts from extreme high‐water temperatures, thereby representing possible thermal refugium for corals against background global warming. Plain Language Summary: We examine the energy balance between water overlying coral reefs and the atmosphere in the desert and tropical coral reefs. We hypothesize that in drier regions higher evaporation rates will cool water overlying the reefs and by that protect the corals from extreme high‐water temperatures and bleaching. We show through rare direct measurements, that the cooling of water caused by sea water evaporation is a key mechanism in mitigating extremely high‐water temperatures that can cause coral bleaching and is especially dominant in coral reefs with strong and dry winds blowing above them. The results support the hypothesis that the meteorology of regions where coral reefs fringe arid deserts provides a thermal refugium for corals against future predicted global warming. Key Points: Evaporative cooling is a key mechanism in mitigating extreme increase in water temperatures and preventing coral bleachingFollowing a marine heatwave, surface energy partitioning varies with air humidity; in drier climates evaporative cooling takes larger roleThe Gulf of Eilat (Aqaba) is identified as an evaporative thermal refugium for the preservation of coral reefs in a warming World [ABSTRACT FROM AUTHOR]