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

Amplitude of interannual variability at different depths The observed vertical profile of the interannual std in the Red Sea ranges from 0.25˚C at 50 m to 0.05˚C below 300 m (S2 Fig, left panel). Interannual std was larger in the Gulf of Aden (0.30˚C at 75 m to 0.10˚C below 300 m), probably due to lateral advection of oceanic waters [17]. In the Red Sea, KAUST shows similar values, even if the shape of the profile is somehow different, with an RMSE and correlation of 0.045˚C and 0.89, respectively. Conversely, the other reference model, GLORYS, shows a very different behaviour, with a maximum reaching 0.6˚C at 75 m and values close to 0.2˚C at 300 m. This leads to a RMSE of 0.2˚C and a correla- tion of 0.69 in the Red Sea. In the Gulf of Aden, GLORYS also shows a wrong profile with a maximum of 0.55˚C at 125 m and minimum of 0.15˚C below 300 m, which is larger than the observed values (S2 Fig, right panel). Most GCM outputs represented the interannual variabil- ity reasonably well, both in the Red Sea and in the Gulf of Aden. The shape of the profile fol- lowed the observed one and maximum std values were below 0.3˚C in most cases, with almost all GCMs showing better skills than the reference GLORYS simulation (see S1 Table). Interannual variability of SST The observed interannual variability of SST is higher than 0.4˚C in the north of the Red Sea while reaches minimum values of 0.2˚C in the southern part (Fig 5). The reference simula- tions, KAUST and GLORYS also show a northward gradient, although smoother and with val-

ues ranging from 0.25˚C to 0.35˚C. Their RMSE is 0.05˚C and their spatial correlation is 0.59 and 0.53, respectively. In the Red Sea, the GCMs show a wide spread of skills, with RMSE val- ues ranging from 0.05˚C to 0.25˚C and spatial correlations ranging from -0.6 to 0.6. In the Gulf of Aden, the RMSE ranges from 0.08˚C and 0.22˚C and between -0.5 and 0.6 for the spa- tial correlation (see S1 Table). An example of a GCM showing good skills (IPSL-CM5a-LR) is presented in Fig 5 (RMSE of 0.07˚C and correlation 0.32). Its behaviour is close to the GLORYS pattern. It represents the northward gradient correctly, although smoother than the Fig 4. Sea surface temperature anomalies with respect to the annual average (in ˚C) in winter (Top) and summer (Bottom), for the observations (first column), average of the selected GCMs (see “Model Selection” section; second column), an example of GCM with good skills (MPI-ESM-LR; third column) and an example GCM with low skills (GFDL-ESM2G; last column). https://doi.org/10.1371/journal.pone.0255505.g004 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 9 / 26