Change Vector Analysis, Tasseled Cap, and NDVI-NDMI for Measuring Land Use/Cover Changes Caused by a Sudden Short-Term Severe Drought: 2011 Texas Event
Round 1
Reviewer 1 Report
Remote sensing is a useful method for the land use/cover monitoring. Short-term severe drought will affect the land cover such as NDVI etc. but normally the land use types will not be changed as quickly as in one or two years. The study used some indexes to analyse the changes after drought, but no new indexes or integrated index to be presented to reveal the overall changes and the reasons of the changes. The results of the study is to indicate that land use/cover changes were affected by both an increase in precipitation and devastating drought, so it will be more reasonable if more samples used to do the comparison with no serious drought. Fieldworks data are also important to improve the analysis to pay more attention on the how the land use/cover changed and the reasons of changes as well.
Author Response
Point 1: Remote sensing is a useful method for the land use/cover monitoring. Short-term severe drought will affect the land cover such as NDVI etc. but normally the land use types will not be changed as quickly as in one or two years.
Response 1: Our paper outlines a sudden short-term severe drought that did in fact alter the land use/cover types in one year. Most of the changes are as a result of declining greenness, i.e. vegetation land cover types changing to bare soil, and vice versa when the drought is over. Post oak savannas and blackland prairies have the ability to regrow that quickly.
Point 2: The study used some indexes to analyse the changes after drought, but no new indexes or integrated index to be presented to reveal the overall changes and the reasons of the changes.
Response 2: That is true. We did not use new indices; instead we developed a methodology built on established NDVI and NDMI in combination with TCT and CVA. We believe this combination is optimal for measuring drought effects.
Point 3: The results of the study is to indicate that land use/cover changes were affected by both an increase in precipitation and devastating drought, so it will be more reasonable if more samples used to do the comparison with no serious drought. Fieldworks data are also important to improve the analysis to pay more attention on the how the land use/cover changed and the reasons of changes as well.
Response 3: We did in fact conduct a widespread accuracy assessment using PCC, ancillary data and expert knowledge. The user's and producer's assessments are available, but for brevity we decided on a summary instead. As for the comparison with no serious drought, the 2010 was a relatively average year that we use to compare the minor drought in 2009 and the more severe drought in 2011.
Reviewer 2 Report
1- Abstract is too long and may bore readers. I highly recommend summarizing the abstract and not exceed 300 words. Sentences that explains the study area and the methodology have the potential to be summarized.
2- In the introduction authors should provide more context for the readers. One of the main missing element is the definition of drought which is adopted for the study, i.e. is it a threshold based or normalized index? What are the hydrological parameters of interest (soil moisture, precipitation and etc)? Then based on these definitions and assumptions authors should provide an update lit review. Another drawback of the current manuscript is the outdated references, all of the references that are cited are old (all are published in 2015 or sooner). While in the field of drought analysis, there has been tremendous number of publication which should be reflected in the current manuscript. The second paragraph of the intro is written in a way that can be pushed back to methodology section. It is providing info about what are the indices that were selected for the analysis with almost zero background info and lit review about them! The last paragraph should summarize the gaps in this field and then with very general explanation (without any technical sentences) authors can explain how they are bridging these gaps. These manuscript is written method oriented which necessitate a thorough revision.
3- Gross Primary Productivity (GPP) is another remotely sensed indicator of drought and how vegetation responses to it. Additionally, ecosystem Water Use Efficiency (WUE) is an index which shows how vegetation responses to the droughts. I was wondering why these metrics are not selected for the study? Also, there has been few attempts on drought recovery analysis, I would like to see a quick review on drought recovery (since it is closely related to the topic), here are top papers on it:
Schwalm, C.R.; Anderegg, W.R.L.; Michalak, A.M.; Fisher, J.B.; Biondi, F.; Koch, G.; Litvak, M.; Ogle, K.; Shaw, J.D.; Wolf, A.; et al. Global patterns of drought recovery. Nature 2017, 548, 202–205.
Yu, Z.; Wang, J.; Liu, S.; Rentch, J.S.; Sun, P.; Lu, C. Global gross primary productivity and water use efficiency changes under drought stress. Environ. Res. Lett. 2017, 12, 014016.
Ahmadi, B.; Ahmadalipour, A.; Tootle, G.; Moradkhani, H. Remote Sensing of Water Use Efficiency and Terrestrial Drought Recovery across the Contiguous United States. Remote Sens. 2019, 11, 731.
4- The 2011 drought was an introduction to the 2012 disasterous drought pretty much all over the CONUS. I was wondering why just drought in 2011 is considered while it continued up to mid 2012. Were the study areas recovered from the dought?
5- Regarding figures 4a and 4b, I was wondering why changes in Houston is sharper than the south Texas? Is that because the color maps are different, or there is a significant difference between these two sites? Finally, if the later is true, how these differences can be interpreted?
6- One general comment on the figures, the fonts for the legends are too small and hard to read, please increase thee font size on figures. Additionally, since there are many white spots in the figures, it would be a good idea to add the boundary line of the study area, for example figure 8b, 8a, 7b and etc.
7- The discussion section is very short and there is almost no evidence for the outlines. I would like to see more references here, for example for each point that has been made, was there any similar study that showed the same result and aligns with the findings of current study?
Author Response
Point 1: Abstract is too long and may bore readers. I highly recommend summarizing the abstract and not exceed 300 words. Sentences that explains the study area and the methodology have the potential to be summarized.
Response 1: Agreed. We have shortened the abstract to less than 300 words by removing information on the study area and methodology.
Point 2: In the introduction authors should provide more context for the readers. One of the main missing element is the definition of drought which is adopted for the study, i.e. is it a threshold based or normalized index? What are the hydrological parameters of interest (soil moisture, precipitation and etc)? Then based on these definitions and assumptions authors should provide an update lit review.
Response 2: Agreed. We have added definitions of drought in both the main body and as a footnote.
Point 3: Another drawback of the current manuscript is the outdated references, all of the references that are cited are old (all are published in 2015 or sooner). While in the field of drought analysis, there has been tremendous number of publication which should be reflected in the current manuscript.
Response 3: Agreed. We have added four recent articles from between 2017 and 2019.
Point 4: The second paragraph of the intro is written in a way that can be pushed back to methodology section. It is providing info about what are the indices that were selected for the analysis with almost zero background info and lit review about them!
Response 4: Agreed. We have moved the second paragraph to the methodology section. But we felt the NDVI and the NDMI are established indices that did not require background information.
Point 5: The last paragraph should summarize the gaps in this field and then with very general explanation (without any technical sentences) authors can explain how they are bridging these gaps. These manuscript is written method oriented which necessitate a thorough revision.
Response 5: Agreed. We outline how our methodology has yet to be implemented in the field of drought impacts on land use/cover. We identify the destructive nature of sudden severe droughts, the novel use of ATAN, and the rate of bare soil expansion. We also flag how our work can add to the debate on climate change.
Point 6: Gross Primary Productivity (GPP) is another remotely sensed indicator of drought and how vegetation responses to it. Additionally, ecosystem Water Use Efficiency (WUE) is an index which shows how vegetation responses to the droughts. I was wondering why these metrics are not selected for the study? Also, there has been few attempts on drought recovery analysis, I would like to see a quick review on drought recovery (since it is closely related to the topic), here are top papers on it:
Schwalm, C.R.; Anderegg, W.R.L.; Michalak, A.M.; Fisher, J.B.; Biondi, F.; Koch, G.; Litvak, M.; Ogle, K.; Shaw, J.D.; Wolf, A.; et al. Global patterns of drought recovery. Nature 2017, 548, 202–205.
Yu, Z.; Wang, J.; Liu, S.; Rentch, J.S.; Sun, P.; Lu, C. Global gross primary productivity and water use efficiency changes under drought stress. Environ. Res. Lett. 2017, 12, 014016.
Ahmadi, B.; Ahmadalipour, A.; Tootle, G.; Moradkhani, H. Remote Sensing of Water Use Efficiency and Terrestrial Drought Recovery across the Contiguous United States. Remote Sens. 2019, 11, 731.
Response 6: We have added these references.
Point 7: The 2011 drought was an introduction to the 2012 disasterous drought pretty much all over the CONUS. I was wondering why just drought in 2011 is considered while it continued up to mid 2012. Were the study areas recovered from the dought?
Response 7: We did not use 2012 because, although the drought continued, the average annual precipitation for 2012 did not represent the year as a drought year.
Point 8: Regarding figures 4a and 4b, I was wondering why changes in Houston is sharper than the south Texas? Is that because the color maps are different, or there is a significant difference between these two sites? Finally, if the later is true, how these differences can be interpreted?
Response 8: It was a color coordination.
Point 9: One general comment on the figures, the fonts for the legends are too small and hard to read, please increase thee font size on figures. Additionally, since there are many white spots in the figures, it would be a good idea to add the boundary line of the study area, for example figure 8b, 8a, 7b and etc.
Response 9: We have increased the font size on all of the figures.
Point 10: The discussion section is very short and there is almost no evidence for the outlines. I would like to see more references here, for example for each point that has been made, was there any similar study that showed the same result and aligns with the findings of current study?
Response 10: We have eliminated the discussion section and instead extended the conclusions. We have addressed points on accuracy, comparisons with the NLCD, and bare soil expansion, and greenness contraction.
Reviewer 3 Report
Rahman and Mesev integrate two advanced multispectral remote sensing transformations (change vector analysis and tassled cap) along with multiple indicies to assess land cover change in two regions of Southern Texas during a major drought.
The study is generally well written and the subject matter is appropriate for Remote Sensing. I have two major critiques. First, the selection of ground truthing/validation points needs to be better explained along with the validation analysis. Second, this study would have more impact if its results were compared to other commonly used products (e.g. NLCD - https://www.mrlc.gov/). Does using CVA and tassled cap better detect drought induced land cover changes than other approaches?
Specific comments:
Line 83: Need to briefly explain atan2 here.
Fig. 1: Put inset boxes on map of the US to show study areas. Scale bars for regional maps need to be larger. Having some lat/long markers on the regional maps would be useful as well.
Line 306: Correct this citation issue
Author Response
Rahman and Mesev integrate two advanced multispectral remote sensing transformations (change vector analysis and tassled cap) along with multiple indicies to assess land cover change in two regions of Southern Texas during a major drought.
Point 1: The study is generally well written and the subject matter is appropriate for Remote Sensing. I have two major critiques. First, the selection of ground truthing/validation points needs to be better explained along with the validation analysis.
Response 2: Apologies if this is not evident. We have expanded the discussion on accuracy assessments using PCC, ancillary data and expert knowledge. We do have the complete user's and producer's accuracy assessment but for brevity we decided to summarize instead.
Point 2: Second, this study would have more impact if its results were compared to other commonly used products (e.g. NLCD - https://www.mrlc.gov/). Does using CVA and tassled cap better detect drought induced land cover changes than other approaches?
Response 2: Agreed. We have referenced the NLCD in the conclusions. However, it is impossible to conduct a direct comparison, simply because of the AOI, timing, and land use/cover categories. We did however, flag the comparison in methodologies.
Specific comments:
Point 3: Line 83: Need to briefly explain atan2 here.
Response 3: Agreed. We have done this.
Point 4: Fig. 1: Put inset boxes on map of the US to show study areas. Scale bars for regional maps need to be larger. Having some lat/long markers on the regional maps would be useful as well.
Response 4: Agreed, we have done this. But the scale bars are impossible to increase without recreating the figures.
Point 5: Line 306: Correct this citation issue
Response: We have done this.
Round 2
Reviewer 1 Report
The paper is well written with interesting topic. The authors have revised the paper and addressed all the comments. Overall it is fine for accept.
Reviewer 2 Report
I would like to thank authors for addressing my comments properly.
