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

MHW conditions ranges among 8 and 12 days per year in all the region. At the end of the cen- tury, under the RCP4.5 scenario, the number of days would increase to 125 days per year in the southern Red Sea and the Gulf of Aden, and around 100 days per year in the rest of the region. Under the RCP 8.5 scenario the situation would be even worse, reaching more than 200 days per year in the southern Red Sea and around 150 days in the northern part and the Gulf of Aden. Consequently, the annual mean intensity (0.6˚C) of the MHWs would increase in the Red Sea, being around 4 (3.6) times larger under the scenario RCP8.5 (RCP4.5). These projections based on GCMs have to be considered as a first approximation and a benchmark result until an ensemble of high resolution ocean models is available. Nevertheless, they clearly point towards the danger of a business-as-usual scenario of emissions and the great potential benefits that mitigation would bring to the Red Sea. Supporting information S1 Fig. Same as Fig 3 but for the outer region. KAUST simulation does not cover this area and is therefore not included in the plots. (TIF) S2 Fig. Vertical profile of the interannual STD (in ˚C) in the Red Sea (left) and in the Gulf of Aden (right) for observations (black line), KAUST (red line), GLORYS (blue line), CMIP5 models (grey lines) and the average of selected GCMs (see “Model Selection” section, green line). (TIF) S3 Fig. Maps of averaged SST anomaly for the period 1985–2005 (in ˚C) with respect to the basin average for each selected GCMs. (TIF)

S4 Fig. Left panel: Vertical profile of averaged temperatures in the Red Sea (in ˚C) for the observations (black), RCP4.5 (blue dashed lines, all models selected) and RCP8.5 (red dashed lines, all models selected) and the ensemble average is represented with a thick line. Right panel: Vertical profile of projected anomalies in the Red Sea for all the selected models under scenario RCP4.5 (blue) and RCP8.5(red). The ensemble average is represented with a thick line. (TIF) S5 Fig. (Top) Anomaly of the observed Sea Surface temperature (blue) and fitted seasonal cycle (red). (Bottom) Intra-seasonal variability of the observed sea surface temperature (grey). (TIF) S6 Fig. Seasonal climatology of the selected CMIP5 models for Present (grey lines) and Future climate (red lines). The values of each model are represented with thin lines, while the ensemble average is represented with thick lines. (TIF) S7 Fig. Simulated changes in different MHWs descriptors presented as the ratio of pro- jected values over the present climate values. (a) annual mean duration, (b) annual mean intensity and (c) annual cumulative mean intensity (d). The colours represent different thresh- olds that have been used to define a MHW (90th, 95th, 98th and 99th percentiles). (TIF) S8 Fig. Marine Heat Wave (MHW) characteristics in the present climate. 95th -Percentile (left panel) in ˚C, number of MHWs per year (middle panel), and the annual mean intensity 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 22 / 26