Assessment of Red Sea temperatures in CMIP5 models for present and future climate

directly impacts on the MHW statistics. We analyse the future MHWs characteristics from the average of the 8 selected GCMs (Fig 10, mid column) and we use the ensemble standard devia- tion (STD) as a measure of the uncertainty (Fig 10, third column and S4 Table). The projec- tions show that MHWs will happen every year, while the average duration of MHW, currently at 8–12 days per year (Fig 10A), will dramatically increase to around 120 ± 35 days per year in the south of the Red Sea and the Gulf of Aden, and around 50 ± 15 days per year in the rest of the region under the RCP4.5 scenario (S9B and S9C Fig). Under the RCP 8.5 scenario, MHW duration is expected to reach more than 200 ± 40 days per year in the South of the Red Sea and around 150 ± 20 days per year in the North, with values larger than 200 ± 60 days per year in the open ocean (Fig 10B and 10C). The mean intensity of the MHWs will consequently increase. At present, the annual mean intensity (AMI) of MHWs ranges from 0.4 to 0.7˚C (Fig 10D), while it would increase to around 1–2 ± 0.20˚C under scenario RCP4.5 (S9E and S9F Fig) and to 2–3 ± 0.4˚C under sce- nario RCP 8.5 (Fig 10E and 10F). Under both scenarios, the spatial pattern of AMI is the same, with the largest values in the Red Sea and the lowest values in the outer region. Finally, we compute the annual accumulative mean Intensity (AAMI), defined as the accumulative excess of temperatures over the threshold. At present it is lower than 4˚C�day in the Red Sea and the Gulf of Aden, increases to 7˚C�day in the northern Red Sea and reaches a maximum of

10˚C�day in the open Indian Ocean (Fig 10G). This spatial distribution is mainly determined by the length of the MHWs (see Fig 10A). For the end of the century, the models project a large increase in the AAMI with a spatial pattern very similar under both scenarios, with the Fig 10. Statistics of MHWs for present conditions (left column), scenario RCP8.5 (ensemble average, middle column) and associated uncertainties (ensemble STD, right column). (a-c) Average length of MHWs in days per year. (d-f) Annual mean Intensity (˚C). (g-i) Annual Accumulative mean Intensity (˚C � day). Note the colorbars for the future scenarios are different than for the present conditions. https://doi.org/10.1371/journal.pone.0255505.g010 PLOS ONE Assessment of Red Sea temperatures in CMIP5 models for present and future climate PLOS ONE | https://doi.org/10.1371/journal.pone.0255505 July 30, 2021 17 / 26