The Spatiotemporal Change of Xiao Qaidam Lake from 1990 to 2020 and Its Potential Hazards
Round 1
Reviewer 1 Report
The article aims at evaluating changes in lake water level and storage under changing climate with implications for humanity. The authors clearly justify the study with good literature and state-of-the-earth land-cover data. The following changes would be required for the manuscript quality to be significantly improved:
Minor Revisions
1) They should indicate what km2/a or km2/10a implies
2) In line 45, they should replace the word 'increase' with 'increasing'.
3) Figure 1 should be replaced with a robust map that describes the location of the study for global readers.
Major Revisions
1) The authors cited the use of climate data in the study and indicated that rainfall and PET changes are responsible for the changes in water level and lake area. A detailed water balance study with all components captured would be required to evaluate the conclusions made by the authors.
2) The authors have used a simple linear regression model for the future prediction of water level and storage ( expansion). This is not ideal as natural and hydrological processes are not linear. The authors should consult relevant literature where appropriate future RCM/GCM climate predictions would be used to drive/create a model for simulating the current and future water balance of the lake considering all relevant hydrological variables.
3) The authors have about 30 years of data but have only used 5 years (2015-2020 ) data to derive their linear model used in future predictions. This may create bias as the long-term data shows three different regimes of water levels from 1990-2020. Long-term data (at least 30 years) would be needed for the analysis and modeling to capture all possible scenarios in the future.
Author Response
Dear Reviewer 1：
Thanks for your valuable suggestions and comments on our manuscript " The Spatiotemporal Change of Xiao Qaidam Lake from 1990 to 2020 and Its Potential Hazards " (Manuscript ID sustainability-1870453). All these comments of reviewers are very important guides to improve the quality of this manuscript. We carefully revised the manuscript and the revision instruction is as follows (review comments in black, the response in blue, the revised parts of the manuscript in red).
Reviewer 1
The article aims at evaluating changes in lake water level and storage under changing climate with implications for humanity. The authors clearly justify the study with good literature and state-of-the-earth land-cover data. The following changes would be required for the manuscript quality to be significantly improved:
Minor Revisions
1) They should indicate what km2/a or km2/10a implies
2) In line 45, they should replace the word 'increase' with 'increasing'.
3) Figure 1 should be replaced with a robust map that describes the location of the study for global readers.
Response: Thanks for your suggestion, and we have made the changes below according to your comment.
- We clarified the meaning of '/10a' and '/a' when they first appeared in the manuscript, in line 43 ('/10a (hereafter, /10a refers to per 10 years)') and line 268 ('/a (hereafter, /a refers to per year)'), respectively.
- Line 45: We replaced the word 'increase' with 'increasing'.
- We replaced Figure 1 with the picture below.
Figure 1. Overview of study area (A: Location of Xiao Qaidam Lake in the Qinghai-Tibet Plateau. B: Location of Xiao Qaidam Lake in the Tataleng River Basin. C: A scene of Landsat OLI image showing the surroundings of Xiao Qaidam Lake, acquired on September 15, 2020, in which site 1, 2 and 3 are the field investigation sites.)
Major Revisions
1) The authors cited the use of climate data in the study and indicated that rainfall and PET changes are responsible for the changes in water level and lake area. A detailed water balance study with all components captured would be required to evaluate the conclusions made by the authors.
Response: Thanks for your suggestion. We agree that it is important to conduct a detailed water balance study on all components. We are sorry that we cannot improve this problem due to the lack of data. Without considering the groundwater, the water balance of a closed flow lake is determined by the precipitation on the lake surface, the runoff into the lake and the evaporation on the lake surface. However, these data need to be measured by special instruments and cannot be obtained at present. Only the meteorological data provided by the Da Qaidam meteorological station nearest to Xiao Qaidam Lake can be used to obtain the precipitation and evaporation. However, the glacier melt water and ground runoff cannot be obtained. Therefore, the development of a hydrological model including precipitation, runoff and evaporation for quantifying the effects of these factors on lake expansion is currently difficult to achieve, due to the absence of reliable data.
2) The authors have used a simple linear regression model for the future prediction of water level and storage (expansion). This is not ideal as natural and hydrological processes are not linear. The authors should consult relevant literature where appropriate future RCM/GCM climate predictions would be used to drive/create a model for simulating the current and future water balance of the lake considering all relevant hydrological variables.
Response: Thanks for your suggestion. We agree that the future RCM/GCM climate predictions should be used to create a model to simulate the future water balance of Xiao Qaidam Lake. However, because the area of Xiao Qaidam Lake is relatively small, the accuracy of the current climate model data is not suitable for Xiao Qaidam Lake even after downscale interpolation. Furthermore, the simulation of future water balance requires a complete historical water balance model. Unfortunately, we are unable to obtain relevant historical hydrological data to establish such a water balance model currently. Therefore, we can only calculate the water volume change based on the available data to predict the future water volume change. At present, many predictions about the future climate of the Tibetan Plateau indicate that the precipitation and temperature of the Tibetan Plateau will increase in the future. Therefore, we assumed that the water balance of Xiao Qaidam Lake in the future is positive, and used the water growth rate in the historical rising stage to simulate the future water storage change. This method has been used by scholars [23], which proves it is feasible.
- Cheng, J.; Liu, C.H.; Liu, K.; Wu, J.S.; Fan, C.Y.; Xue, B.; Ma, R.H.; Song, C.Q. Potential impact of the dramatical expansion of Lake Qinghai on the habitat facilities and grassland since 2004. Journal of Lake Sciences 2021, 33, 922-934. DOI: 10.18307/2021.0325.
3) The authors have about 30 years of data but have only used 5 years (2015-2020) data to derive their linear model used in future predictions. This may create bias as the long-term data shows three different regimes of water levels from 1990-2020. Long-term data (at least 30 years) would be needed for the analysis and modeling to capture all possible scenarios in the future.
Response: Thanks for your suggestion. According to the current water level data (2010-2020), we can only calculate the water volume change after 2010. The lake was in the shrinking stage from 2010 to 2015, but the water level increased year by year from 2015 to 2020. Multiple future climate data indicate an increase in precipitation and temperature in the future in the Qaidam Basin, based on which, we assumed that the water volume of Xiao Qaidam Lake will be in a positive balance in the future. Therefore, we simulated the future water volume change of Xiao Qaidam Lake with the water volume growth rate from 2015 to 2020.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
In this study, the authors studied the spatiotemporal change of Xiao Qaidam Lake for three decades and evaluated its potential hazards. Overall, the study is methodologically sound, with promising results and discussion. However, there are major comments to be addressed:
Specific Comments:
(i) Introduction Section: Huge modification/revision required. The introduction section did not provide much evidence of the necessity of performing the research. Although some previous studies were provided, however, the research gap was not highlighted. Also, provide the objectives of the study.
(ii) The unit for changes per year should be "km/y" instead of "km/a"
(iii) Discussion on evapotranspiration is heavily limited. More relevant discussions are necessary to improve the quality of the manuscript. Else, I do not find the necessity in calculating the ET in the study.
You may refer to the study as follows:
1. Wong, Y.J., Shiu, H., Chang, J.H.H., Ooi, M.C.G., Li, H., Homma, R., et al. (2022). Spatiotemporal impact of COVID-19 on Taiwan air quality in the absence of a lockdown: Influence of urban public transportation use and meteorological conditions. Journal of Cleaner Production, doi:10.1016/j.jclepro.2022.132893.
(iv) Where are the yearly simulation results of section 4.3? Elaborate on the methods used to simulate the future conditions of Xiao Qaidam Lake.
(v) Provide the limitation section of this study. I believe this research are focusing on the business-as-usual scenario for simulation. Although the simulated results seem promising, with the interference of the government, the results might be inaccurate.
You may refer to the study as follows:
1. Wong, Y.J., Shiu, H., Chang, J.H.H., Ooi, M.C.G., Li, H., Homma, R., et al. (2022). Spatiotemporal impact of COVID-19 on Taiwan air quality in the absence of a lockdown: Influence of urban public transportation use and meteorological conditions. Journal of Cleaner Production, doi:10.1016/j.jclepro.2022.132893.
(vi) The title of the study is confusing. I do observe the temporal aspects of the study, however, the spatial aspects are limited in this study. Please revise the title. Changes in the research area or its depth are not considered spatial aspects. Spatial aspects should include discussions of detailed spatial classification in the eight compass octants.
You may refer to the study as follows:
Ndiaye, P. M., Bodian, A., Diop, L., Deme, A., Dezetter, A., Djaman, K., & Ogilvie, A. (2020). Trend and sensitivity analysis of reference evapotranspiration in the Senegal river basin using NASA meteorological data. Water, 12(7), 1957.
(vi) Line 343-345 are hard to be understood without the support of a figure. Revise and restructure the content.
(vii) Conclusion section: Must be improved and provide insights and highlight the take-home message for the readers. The current conclusion is more like a repetition of results and discussion.
(viii) Line 20-23: very confusing. Please revise. How come the increase in annual precipitation and decrease of ET are the main reasons for the rapid expansion of Xiao Qaidam Lake?
Author Response
Dear Reviewer 2：
Thanks for your valuable suggestions and comments on our manuscript " The Spatiotemporal Change of Xiao Qaidam Lake from 1990 to 2020 and Its Potential Hazards " (Manuscript ID sustainability-1870453). All these comments of reviewers are very important guides to improve the quality of this manuscript. We carefully revised the manuscript and the revision instruction is as follows (review comments in black, the response in blue, the revised parts of the manuscript in red).
Reviewer 2
In this study, the authors studied the spatiotemporal change of Xiao Qaidam Lake for three decades and evaluated its potential hazards. Overall, the study is methodologically sound, with promising results and discussion. However, there are major comments to be addressed:
Specific Comments:
1) Introduction Section: Huge modification/revision required. The introduction section did not provide much evidence of the necessity of performing the research. Although some previous studies were provided, however, the research gap was not highlighted. Also, provide the objectives of the study.
Response: Thanks for your suggestion, and we have made the changes below according to your comments. We added some contents in Introduction Section:
Line51-54: 'The expansion or even collapse of some lakes will inundate large areas of grassland and traffic trunk lines, seriously affecting the surrounding environment and traffic, and further affecting the production and life of local residents [23,24].'
Line75-79: 'At present, the researches on Xiao Qaidam Lake mainly focus on the study of its chemical composition [32], surface sediments [33] and the development of mineral resources [27], but do not pay attention to the impact of the expansion of Xiao Qaidam Lake on G3011 and S20. Therefore, long-term monitoring of Xiao Qaidam Lake is very important for disaster prevention. '
2) The unit for changes per year should be "km/y" instead of "km/a"
Response: Thanks for your suggestion, but according to some references (such as references 10, 23 and 26 in this paper.), we prefer to write "km/a".
10.Zhang, Y.; Yao, X.; Zhou, S.; Zhang, D. Glacier changes in the Sanjiangyuan Nature Reserve of China during 2000–2018. J. Geogr. Sci. 2022, 32, 259-279. DOI: 10.1007/s11442-022-1946-0.
23.Duan, S.Q. Lake evolution in the Qaidam Basin during 1976-2015 and their changes in response to climate and anthropogenic factors. J. Lake Sci. 2018, 30, 256-265. DOI: 10.18307/2018.0125.
26.Du, Y.E.; Liu, B.K.; He, W.G.; Zhou, J.P.; Duan, S.Q. Analysis on the variation and cause of the lake area in Qaidam Basin from 1976 to 2017. Journal of Glaciology and Geocryology 2018, 40, 1275-1284. DOI: 10.7522/j.issn.1000-0240.2019.0304.
3) Discussion on evapotranspiration is heavily limited. More relevant discussions are necessary to improve the quality of the manuscript. Else, I do not find the necessity in calculating the ET in the study.
Response: Thanks for your suggestion. Evaporation is an important factor affecting the expansion of lakes. However, the pan evaporation measured by the meteorological station is incomplete because there are some missing measurements, and most of the years are the evaporation capacity of small evaporation dishes, the evaporation capacity of large evaporation dishes is only from June to September after 2004. Comparison shows that there is a big difference between the evaporation amount of large evaporation dish and small evaporation dish, that is, the evaporation amount measured by small evaporation dish is bigger than that of large evaporation dish. Therefore, we adopted the Penman formula which is proved by scholars to be also suitable for calculating the evapotranspiration of the lake to calculate the potential evapotranspiration of Xiao Qaidam Lake. In Section 5.1, evapotranspiration is analyzed as a factor affecting lake expansion, and we describe the change of evaporation and its correlation with the area change of Xiao Qaidam Lake.
4) Where are the yearly simulation results of section 4.3? Elaborate on the methods used to simulate the future conditions of Xiao Qaidam Lake.
Response: Thanks for your suggestion. In section 4.3, the future evolution simulation results of Xiao Qaidam Lake are described based on the water level in three years of 2024, 2033 and 2041, without calculated annual change results. The above three important water levels (times) visually reflect the changes in the shoreline of Xiao Qaidam Lake and help readers understand the future spatial evolution of the lake. And we elaborated on the methods used to simulate the future conditions of Xiao Qaidam Lake in lines 228-238. ' Referring to the area and water level of Xiao Qaidam Lake in 2020, we utilized the contour tool in the 3D analysis tools module in ArcGIS10.6 software to calculate the corresponding relationship between elevation value and area in the step of 1 m, simulate the inundation range of Xiao Qaidam Lake at different altitudes and correct the lake range by eliminating the unconnected area in consideration of the connectivity of lake expansion [23]. Finally, the water reserve increment of Xiao Qaidam Lake at different altitudes can be obtained by using formula (2). By calculating the change rate of water volume and the change of the simulation results at different altitudes relative to the lake water storage in 2020, we can obtain the time required for Xiao Qaidam Lake to reach different simulation ranges, and then conduct risk assessment on the surrounding grassland, roads, power poles and other infrastructures. '
5) Provide the limitation section of this study. I believe this research are focusing on the business-as-usual scenario for simulation. Although the simulated results seem promising, with the interference of the government, the results might be inaccurate.
Response: Thanks for your suggestion. Your suggestions are of great significance to improving the quality of our manuscripts. According to your comment, we have added the limitation section of this study in lines 260-275 '3.2.4 Assumptions and limitations Many studies show that the average temperature and precipitation on the Qinghai-Tibet Plateau will increase in the future based on CMIP6 [51-53]. According to the research of Zhang et al. [53], the precipitation of Qaidam Basin from 2031 to 2050 under various scenarios of GCM model shows an increasing trend, of which the SSP370 scenario is the most sensitive to the precipitation change, and the precipitation increase can reach 30% compared with the base period. Therefore, we assume that the water volume of Xiao Qaidam Lake will be in a positive balance in the future. In addition, due to the lack of data including lake surface precipitation, evaporation and runoff into the lake, it is impossible to quantify the contribution of precipitation, evaporation and melting water of glacier and frozen soil to lake expansion. Meanwhile, it is difficult to accurately predict the future meteorological conditions of Xiao Qaidam Lake because the area of Xiao Qaidam Lake is much smaller than the spatial resolution of GCM model. Finally, the simulation results of this study are under ideal conditions, that is, without the intervention of the government (filling high subgrade, drainage, etc.), and the results may deviate from the actual situation. '
6) The title of the study is confusing. I do observe the temporal aspects of the study, however, the spatial aspects are limited in this study. Please revise the title. Changes in the research area or its depth are not considered spatial aspects. Spatial aspects should include discussions of detailed spatial classification in the eight compass octants.
Response: Thanks for your suggestion. We did study the change characteristics of Xiao Qaidam Lake in all directions, but only described the variability in the direction of its main expansion, especially in the west and south, which has important implications for the road and is the focus of this paper. The spatial changes of Xiao Qaidam Lake are in lines 300-309.
7) Line 343-345 are hard to be understood without the support of a figure. Revise and restructure the content.
Response: Thanks for your suggestion. It is our fault that the figure is not pointed out. We made the following changes in lines 427-430 'For example, when the water level of Xiao Qaidam Lake rises to 3180 m, 3184 m and 3187 m, the submerged grassland area will reach 19.85 km2, 52.37 km2 and 70.08 km2, respectively (Figure 6B), which may have a direct impact on the production and life of local residents.'
8) Conclusion section: Must be improved and provide insights and highlight the take-home message for the readers. The current conclusion is more like a repetition of results and discussion.
Response: Thanks for your suggestion. Your suggestions are of great significance to improving the quality of our manuscripts, and we have made the changes below according to your comments. We replaced 'In 2020, the lake area reached a peak (131.15 km2), which was 1.85 times the lake area in 1990, and the corresponding lake water volume increased by 0.31 km3. Especially after 2015, the expansion rate of the lake has accelerated significantly, and the annual change rate is as high as 8.54 km2/a.' with 'Especially after 2015, the expansion rate of the lake has accelerated significantly, and the annual change rate is as high as 8.54 km2/a. In 2020, the lake area reached a peak (131.15 km2), which was 1.85 times the lake area in 1990, and the corresponding lake water volume increased by 0.31 km3'. And we added 'The change of Xiao Qaidam Lake has a reference significance for the study of lakes in the Qaidam Basin, and more attention should be paid to the expanding lakes similar to Xiao Qaidam Lake near the traffic trunk lines. The relevant departments shall consider the surrounding environment and its possible changes in the future when planning the roads to minimize the losses. It is hoped that in the future, there will be more open meteorological and hydrological data with higher accuracy to make the prediction of lake changes more accurate, which will be conducive to disaster assessment and reduce property losses. ' in lines 534-540.
9) Line 20-23: very confusing. Please revise. How come the increase in annual precipitation and decrease of ET are the main reasons for the rapid expansion of Xiao Qaidam Lake?
Response: Thanks for your suggestion. We analyzed the correlation between the lake area and precipitation and evaporation, and found that the lake area was positively correlated with precipitation and negatively correlated with evaporation. With the increase of precipitation and the decrease of evaporation, the water source increases and the consumption decreases, resulting in the positive balance of lake water, water level rise and area expansion. So we come to the conclusion that 'Both the increase of annual precipitation (12.63 mm/10a) and the decrease of potential evapotranspiration (-13.38 mm/10a) since 1990 are the main reasons for the rapid expansion of Xiao Qaidam Lake'.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Please we believe the author has done what is possible in the study area to implement the study.
Reviewer 2 Report
The authors have substantially addressed and revised the manuscript. The current manuscripts provides much better and clearer details for readers to understand the methodology as well as the results and discussion sections
