Let me start by saying that I wholeheartedly enjoyed reading this manuscript and I applaud the authors for their effort. This manuscript is not a research paper but documents an educational/outreach activity that cuts across both hydrology (ET) and micrometeorology (urban heat).  I like the manuscript a lot. One aspect I like in particular is that the authors document all the details, from the theoretical basis, instruments, to lab set-up, to sample question, etc. They even include a calculation spreadsheet that automatically calculate fluxes. Another aspect I like is that the authors always think about the broad context (e.g., understanding coupled natural-human systems and promoting environmental justice). 

I only have 2 minor comments (they are really just suggestions or clarifying questions). The first is related to the treatment of ground heat flux. The current treatment of ground heat flux (making it zero) is OK but perhaps misses the opportunity to teach/discuss another aspect of urban heat.  Urban heat islands are no doubt associated with the lack of evapotranspiration due to the use of impervious surfaces in cities. Nonetheless, urban heat islands tend to be stronger at night, which is also (perhaps more) related to the fact that these impervious materials tend to store more heat during the day and release them at night (see e.g., Li et al. 2019, Urban heat island: Aerodynamics or imperviousness?.Sci. Adv.5,eaau4299(2019).DOI:10.1126/sciadv.aau4299). This might be why the energy balance approach tends to produce higher ET rates because it did not take into account the heat storage, which is probably not a small term at such time scales for dry surfaces. 

My second comment is related to the temporal change of surface temperature and as a result the temporal change of sensible heat flux. In theory the surface temperature should change throughout during the 90-120 minutes of lab session. Am I right? If the students only take the final surface temperature, does this mean that only the sensible heat flux at the final stage can be calculated? Is this final sensible heat flux used as an approximation for the sensible heat flux during the entire lab session? It would be better to make this clear in one or some of the equations in section 4.2. 

Dan Li

Dear authors, I enjoyed reading your manuscript and find it relevant for future potential application at other UNIs and cities.  You have presented an ET educational activity that integrates theory with practice and links ET and UH. Also, you have provided supplementary material which can help future users to implement your proposed method and design of teaching. I have a few notes for you to address:

1) What are K-12 classrooms? Add explanation in manuscript at appropriate place.

2) Figure 1 - Add a note that describes the abbreviations in Figure 1.

3) It would be good to discuss a bit the implications of setting G as 0.

4) In Section 4.1 you mention “ten land surface cores”, while in Figure 2 are shown 15 cores. Check this for consistency.

5) You used “bare soil”, can you add a short info on which type of soil was used?

The HESS pre-print by Blount et al., summarizes a new hands-on approach to teaching both evapotranspiration and the urban heat island concepts in university courses, while also identifying ways to adapt the activity toward the public. The paper summarizes the theoretical framework of the energy and water balance methods of measuring ET and how they connect to UHI. The authors then summarize their activity, where small cores of different materials common in urban areas (soil with grass, mulch, gravel, etc.) are wetted up, and ET is estimated through both water balance (mass water loss) and energy (temperature change) methods. Students can then compare how different land types and different measurement methods relate to the concept of UHI. It is a great, stand-alone description for anyone teaching ET, going from the theoretical basis all the way to the activity and questions to ask students. It also has great ways to push students to think about historical development of cities, structural racism, and environmental justice. I’m already scrambling to see if I can get my hands on an IR thermometer and heat lamp for a discussion of ET coming up this week in my class.

I think one potential area for improvement of the paper (and activity) as written is that it focuses so much on difference in land cover impact on ET and linking to UHI and a bit less on leveraging this experiment to help students understand differences in measurement method. To me, this misses a key opportunity to help students more clearly understand the concepts of potential evapotranspiration and actual evapotranspiration, which I have found students at the same level as the authors’ (undergraduates) struggle with. I think a bit more explanation of how to use the activity to explain AET and PET would be a great addition, and they could point to then how this activity could to lead into a discussion of the Budyko Curve for anyone who covers that within a course (I realize this last part may be out of scope for many undergraduate courses) or aridity, or water scarcity, or many other things tied to the AET vs. PET balance.

The language of the example write ups (section 6.2) is very technical- it’s not the kind of language I’ve seen my students use (for example phrases like “limited moisture retention” and “transpiration potential”). I know students vary in their level of writing and understanding, but were these drawn from student responses? If you have actual student responses, could you summarize some of the phrases from students? I know you may not have had an IRB, which complicates this. But I think two levels of example- that of an expert and that of a student- would be very helpful to set expectations of faculty members/teachers at the correct level.

Typo I found: line 108 has a comma after “climate change” that seems to me is unnecessary

1. Does the paper address relevant scientific questions within the scope of HESS?

It is a little unclear to me what type of manuscript type this has been submitted as, but I do believe it clearly falls under “Education and Communication” of a key hydrologic topic within the scope of HESS.

2. Does the paper present novel concepts, ideas, tools, or data?

Yes, the paper presents a novel approach to teaching ET and linking it to the urban heat island concept. In addition, it could be expanded to more clearly discuss differences between PET and AET, which would be a strong suggestion to the authors.

3. Are substantial conclusions reached?

Not sure how much this fits for an education paper, but yes, they show results from running this activity that show it works.

4. Are the scientific methods and assumptions valid and clearly outlined?

Yes.

5. Are the results sufficient to support the interpretations and conclusions?

Yes

6. Is the description of experiments and calculations sufficiently complete and precise to allow their reproduction by fellow scientists (traceability of results)?

Yes, the set up description is very strong.

7. Do the authors give proper credit to related work and clearly indicate their own new/original contribution?

Yes, the paper does a very good job summarizing the theoretical background behind water and energy approaches to ET, then shows how their activity leverages that theory to teach the concepts in a more ‘hands-on’ way.

8. Does the title clearly reflect the contents of the paper?

Yes

9. Does the abstract provide a concise and complete summary?

Yes

10. Is the overall presentation well structured and clear?

Yes

11. Is the language fluent and precise?

Yes

12. Are mathematical formulae, symbols, abbreviations, and units correctly defined and used?

Yes

13. Should any parts of the paper (text, formulae, figures, tables) be clarified, reduced, combined, or eliminated?

I’d suggest the caption for Figure 1 should define all variables shown so it can stand alone, if needed.

14. Are the number and quality of references appropriate?

Yes

15. Is the amount and quality of supplementary material appropriate?

Yes, many thanks for sharing all of the supplemental instructor resources!