I'm glad my previous comments were found to be useful. I can fully understand why the authors have not wished to repeat the future projections using the Penman method applied to the original CMIP5 projections (this would be a large undertaking) and to makes sense to try to use an approproximation for this by adjusting the Thornwaite-based results. It seems that this works reasonably well for the range of PET seen in the historical period. However, I think it is important to know how well this cover the range of PET projected for the future - if the maximum future PET is within or only slightly above the range tested in figure 3, then we can probably be confident that this method yields a good estimate of the what a Penman-based estimate would give for the future. However, if the future PET extends well above this range, the projections should therefore be viewed with more caution. Therefore I recommend that the authors give some information on the range of PET projected for the future, preferably shown on figure 3 in some way, so that the reader is aware of possible limitations of this approximation.
I think it would also be worth explaining why Thornthwaite was used in the first place. e.g. is it following on form previous work?
In lines 345-346 of the revised manuscript, the authors say:
"Therefore, a more physically-basedbased PET calculation method (such as the Penman method) needs to be considered in the GCMs". I don't think "in the GCMs" is really what is meant here, as the authors are referring to their own calculations not those carried out *in* the GCMs - the GCM land surface schemes make their own calculations of ET, but those are not used here. The phrase "in the GCMs" should therefore be dropped from this sentence.
Finally, a technical correction is needed, which I must admit I noticed first time but forgot to include in my previous review (apologies). In Table 1, the resolution of all the CMIP5 GCMs is given as 1*1 degree. However, this is not the resolution of the GCMs - I assume that it must be the resolution of the post-processed data obtained by the authors via the Canadian Climate Centre (presumably the data have been re-gridded from the native resolution to 1 degree resolution). This should be clarified. |