|The present study ("Implementation of a new crop phenology and irrigation scheme in the ISBA land surface model using SURFEX_v8.1") introduces a new phenology and irrigation scheme for the ISBA LSM and evaluates its performance against observational data from a densely irrigated region of Nebraska (USA). |
It becomes clear that the main improvement for better performance regarding LAI and GPP stems from the improved phenology with prescribed emergence and harvest dates. The irrigation scheme does not add much with respect to the aforementioned variables, but provides reasonable water use values with respect to observations.
I have been only involved now where the manuscript is already in round 3 of revisions. Therefore I interpret my main responsibility is to judge whether the present version of the manuscript is fit for publication and the authors have taken care of all points raised by the two previous reviewers. This is the case. The only thing missing in terms of reproducibility of the study is a step-by-step explanation of how to use the data in the ZENODO archive(s) together with the SURFAX code to redo the simulations and any potential postprocessing scripts. I suggest to add a README file to the ZENODO archive containing this information. The manuscript itself is written very clearly and I enjoyed reading it.
However, since I read the article for the first time and with fresh eyes, I noticed some minor things that could still be improved and I ask the authors to include them in the final version of their manuscript. I apologize for this, because I know that for authors, introducing new reviewers late in the review process is annoying, but at the same time I hope that they seize the opportunity to further increase the quality of their (already good) manuscript by including my remarks. I am looking forward to read about future work on the global evaluation of the phenology and irrigation schemes in ISBA.
More general comment:
What purpose is the model generally used for? One main purpose of crop models is to provide harvest amounts. Therefore I was wondering, why (additional to the irrigation water amount, LAI and GPP) you did not look at how harvests compared between the 3 model versions? I would suspect that here you might see a stronger difference between ISBA_pheno and ISBA_pheno_irr, suggesting that including irrigation is worth while.
- lines 58-72: It it great that you implement irrigation into ISBA. However your are making it sound like just very few other models have implemented irrigation. I don't think that is a fair point, as basically all crop models have implemented it. Many of them can (depending on your definition) be regarded as a LSM.
- lines 129-134: Your argument for having decreasing SWI thresholds for subsequent irrigation events is weak. The root fraction is already part of SWIroot_zone.
Additionally: If the irrigation water amount is still 30mm for subsequent irrigation events triggered at lower SWI, you would need more water to fill the soil again, right?
- lines 149-152: Please add that this first part describes sprinkler irrigation settings. Drip/flood description only starts in line 171.
- line 193: 20 non-irrigated + 20 irrigated * 3 types is 80
- line 240: The random picking of harvest/emergence date seems to complicate things and you did not mention it previously. However it is relevant, because irrigation would not be allowed, if emergence is happening later or harvest earlier than the default date.
- lines 313-314: I suggest to change “simulated number of yearly irrigation events” to “simulated irrigation water amount”. Events cannot be compared to amounts and you explain how the conversion is done in the next sentence.
- lines 360-364: Explain how you calculate the precipitation bias in Fig S4.6, either here in the text or in the figure caption. I assume it is ERA5 data minus weather station data for that pixel, right? You are arguing that the bias in ERA5 is the reason for too high simulated irrigation. But the absolute bias is also high in 2000 and 2005. If you want to take the relative change (2010 was a wetter year than 2005 and 2000) into account, I would think that this could be best seen in precipitation bias in [%] with respect to absolute precipitation. This should show higher deviations for 2010 than 2000 and 2005 and serve your point.
- lines 369-371: Where do I see this Boedhram data?
- line 371: You could mention here that you will do a comparison across all “nature types” in the next section.
- line 380: I assume you meant to say “without phenology (and without irrigation)” instead of “without irrigation” – the main difference here is the phenology, not the irrigation
- lines 409-410: I would argue that the wider distributions are due to the effect of not having imposed emergence and harvest dates for natural vegetation.
- line 489: I would say, that rather than “empirical” it is “random”.
- line 539: It is really hard to see the difference, please add a third panel with the difference to this figure.
- Table 1:
List all possible values as well, not only the default.
Irrigated “nature“ type, I understand that the surface type is called this way in ISBA, but to call a crop “nature” sounds wrong to me. How about (at least in the paper), you rename it to “vegetation”, or what it is: “land surface type”.
An irrigation water “turn” could be called “event”.
Explain the abbrv. “SWI” in the caption.
I believe a “time lapse” is sth. else, how about “time interval”/”lapse of time”/”time span”?
- Figure 3: I suggest to use 5-year steps for the x-axis starting 1985
- Figure 7: This figure is never mentioned in the text