Spatio-Temporal Variations in Farmland Water Conditions in the Yanhe River Basin

Round 1

Reviewer 1 Report

This paper estimated the spatial and temporal variation of land moisture profits and losses in Yanhe river basin from 2003 to 2015. The authors also attributed the main driving factors to precipitation and specific humidity. It is meaningful for the farmland water management in the basin. This study is within the scope of the journal. In general, I'm supportive of publication of this paper. However, prior to publication, some concerns need to be addressed.

Figure 4 shows the spatial pattern changes of land moisture profit and loss in 2003, 2007, 2011, and 2015. It can be seen that water deficit becomes worse in 2007 but alleviated in 2011, and then becomes worse in 2015 again in comparison with 2003. I am wondering which factor dominates this pattern change, if possible, the authors are encouraged to provide the spatial change of dominate factor in the corresponding year. Figure 5 presents the correlation plots on the possible influencing factors, are they the mean value of the whole basin? The spatial pattern may have different characteristics among the upper, middle, or lower of the basin, so, this would have a large impact on the results. Therefore, if possible, the authors are encouraged to divide the basin into sub-areas for the factor (at least for precipitation and specific humidity), and then give more specific correlations for each part of the basin.

Other small modifications are also needed to improve the paper, such as:

Introduction:

The authors tried to demonstrate the good performance of PM method in estimating ETo or ETa. Therefore, more results or characteristics of other models are needed to be clarified. Here is a example reference on Priestley-Taylor (PT) model:

AI, Zhipin; YANG, Yonghui. Modification and validation of Priestley–Taylor model for estimating cotton evapotranspiration under plastic mulch condition. Journal of Hydrometeorology, 2016, 17.4: 1281-1293.

The following work on the crop coefficient used in crop water consumption are relevant to the authors’ intention in several descriptions:

AI, Zhipin, et al. Characteristics and influencing factors of crop coefficient for drip-irrigated cotton under plastic-mulched condition in arid environment. Journal of Agricultural Meteorology, 2018, 74.1: 1-8.

Data sources and methods:

The authors used crop water requirement and land surface actual evapotranspiration to estimate the key variable in this paper (MPLD), therefore, which method is used to calculate the actual evapotranspiration, it seems no such description in the text at present.

Author Response

- Line 423: Figure 4 shows the spatial pattern changes of land moisture profit and loss in 2003, 2007, 2011, and 2015. It can be seen that water deficit becomes worse in 2007 but alleviated in 2011, and then becomes worse in 2015 again in comparison with 2003. I am wondering which factor dominates this pattern change, if possible, the authors are encouraged to provide the spatial change of dominate factor in the corresponding year.

Response: Thank you for your careful review. Following your comment, we plotted a line graph of six meteorological factors and MPLD changes. The revisions can be found in subsection 5.

5.1.2. Changes in impact factors in different years

In order to clearly show which factors dominate the changes in MPLD, we plotted a line graph of six meteorological factors and MPLD changes(Fig. 7). By comparing the trend of the line chart, we can clearly see that in 2007, precipitation, air pressure, near-surface air than humidity and air temperature are exactly opposite to the trend of MPLD，the combination of the four causes MPLD to rise. In 2011, the content of combination has changed, and the combination of precipitation, radiation, near-surface air specific humidity and wind speed led to a decline in MPLD. In 2015, precipitation, near-surface air combined with humidity and temperature led to an increase in MPLD.

 

Line 448: Figure 5 presents the correlation plots on the possible influencing factors, are they the mean value of the whole basin? The spatial pattern may have different characteristics among the upper, middle, or lower of the basin, so, this would have a large impact on the results. Therefore, if possible, the authors are encouraged to divide the basin into sub-areas for the factor (at least for precipitation and specific humidity), and then give more specific correlations for each part of the basin

Response: Thank you for your careful review. Following your comment, we calculated the impact of meteorological factors on each grid unit on MPLD. The revisions can be found in subsection 5.

5.1.3. Spatial performance of impact factors on MPLD

In order to clearly show the influence of meteorological factors on MPLD in the upstream, midstream and downstream of the basin, we also calculated the impact of meteorological factors on each grid unit on MPLD(Fig. 8). We found that the impact of precipitation on the MPLD in the basin is large, while the impact of air pressure on the MPLD is small, some high-value areas are only distributed in the middle and downstream. Radiation has a great influence on the downstream areas of the basin, but little on the upstream and downstream areas of the basin. The near-surface air has a greater impact than the upper and middle reaches of the wet-watershed, and has a small impact on the downstream of the basin. The midstream area in the river basin is greatly affected by the air temperature, while the upstream and downstream areas are less affected by this factor. The upper reaches of the basin are strongly affected by wind speed, while the middle and lower reaches only have some inhomogeneous scattered high-value areas.

 

Line 50: The authors tried to demonstrate the good performance of PM method in estimating ETo or ETa. Therefore, more results or characteristics of other models are needed to be clarified.

Response: Thank you very much for your proposal. We have carefully read the two articles you mentioned and have benefited a lot. At the same time, we also quoted the literature you mentioned in this study. The revisions can be found in the third and fourth paragraphs in subsection 1 (Introduction).

 

Line 243: The authors used crop water requirement and land surface actual evapotranspiration to estimate the key variable in this paper (MPLD), therefore, which method is used to calculate the actual evapotranspiration, it seems no such description in the text at present.

Response: Thank you for your careful review. Following your suggestion, we added a calculation about ET. The revisions can be found in the appendix B.

Author Response File: Author Response.pdf

Reviewer 2 Report

I completed the review of "SPATIO-TEMPORAL VARIATIONS IN FARMLAND WATER CONDITIONS IN THE YANHE RIVER BASIN". According to the IPCC, the climate has changed tremendously in the last 100 years. The authors assess the climate change impacts on the Yanhe River basin from 2003-2015 by quantifying moisture profits using the modified Penman-Monteith method. This method has been proposed by the FAO since 1998 and is widely used around the world. It is used to calculate potential evapotranspiration and actual evapotranspiration. With the use of meteorological data and indexes such as MODIS and NDVI, moisture profit and loss changes were analyzed for this river basin. The final results indicate that the Yanhe River basin experienced a water shortage by 34.83%. Wang et al. (2019) acknowledges other studies to conclude that meteorological data such as precipitation, wind speed, and temperature significantly influence changes in moisture profit and loss while varying considerably in during different seasons. The semi-arid region of northwestern china that the Yahne River basin is located is expected to become warmer and drier which will be problematic for water use.

Overall, the manuscript reads well and has interesting findings (mentioned above) on a very timely topic. Thus, I recommend accepting this article after moderate English editing. References are not alphabetic order in citation list (at the end).

 

Author Response

References are not alphabetic order in citation list (at the end).

Response: Thank you for your careful review. Following your suggestion, we modified the format of the reference.

Author Response File: Author Response.pdf

Reviewer 3 Report

Review of the paper “Spatial-Temporal Variations in Farmland Water Conditions in the Yanhe River Basin” by Wang et al. submitted to water.

General comments:

In the abstract, this paper mentions that the purpose of this work is to understand the influence of climate change on water cycling and water resources. It is an interesting topic. However, in my view, this manuscript is more like a project report but not journal paper as the scientific creativity is not clear.

General comments:

a lot of important details were missed in the manuscript. Such as (1) how did each variable in Equation (1) were calculated in this study? (2) How did you get the spatial distributed meteorological data from three sites? Section 5.1.2 is completely not appropriate to appear there as it is completely a review of these previous studies. Section 5.2 gives three reasons for the water deficit in the basin. However, I think only the first one can be supported by this study for three reasons: (1) the water deficit is identified by MPLD in this study; (2) this paper never mentions the effects of vegetation on MPLD, thus it is not reasonable to infer the vegetation restoration effects on MPLD; and (3) similarly, this paper never mentions how economic development and population growth affect farmland moisture. In the paper, remote sensing data, model derived data, and site observed data were used. However, they are in different spatial and temporal resolution. Please add additional discussion on the uncertainty of this study.

Specific comments:

Section 3.1 I think average temperature should be air temperature. How did you get table 1, please add more explanations on it. I did not find the temporal resolution of your calculated MPLD, yearly? From figure 3, it is difficult to draw any conclusion on the trend of MPLD. The water shortage trend is also not clear. For example, the Acute percentages were very small from year 2009 to 2014 comparing to year 2004-2008.

Author Response

Line 12: In the abstract, this paper mentions that the purpose of this work is to understand the influence of climate change on water cycling and water resources. It is an interesting topic. However, in my view, this manuscript is more like a project report but not journal paper as the scientific creativity is not clear.

Response: Thank you for your careful review. Following your suggestion, we made a lot of changes to the manuscript. We believe that the scientific idea of this research lies in the particularity of the study area. The Yanhe River Basin is a typical semi-arid area in China. The agriculture in the basin is very developed, but the climatic conditions in the basin cause the agricultural development to be restricted by water. Therefore, we believe that the discussion on the water surplus and loss of cultivated land in the Yanhe River Basin will help the management of water resources in the basin, and also provide advice on agricultural development in other semi-arid regions of the world.

 

Line 216: How did each variable in Equation (1) were calculated in this study?.

Response: Thank you for your careful review. Following your suggestion, we added the formula for the calculation of the equation (1). The revisions can be found in the appendix A.

 

Line 186 How did you get the spatial distributed meteorological data from three sites.

Response: Thank you for your careful review. In order to ensure the accuracy of the edge site, we first use AUSPLIN to interpolate the meteorological data of the entire Loess Plateau, and then extract the meteorological data of the Yanhe River from the interpolated data.

 

Section 5.1.2 is completely not appropriate to appear there as it is completely a review of these previous studies..

Response: Thank you for your careful review. Following your suggestion, we have revised and deleted this part of the content. The revisions can be found in the subsection 5.

5.2. Comparison with other research findings on water gains and losses

The previous studies on the changes in water surplus and loss in the Loess Plateau of China and the northwestern arid regions in China show that the water deficit situation in this region was grim, mainly as a result of climatic changes[43-45]. Meteorological factors such as precipitation, temperature and wind speed have a great influence on the change of water surplus and loss, especially precipitation was the dominant factor influencing water evapotranspiration changes[46-48]. The study also indicate that some factors like temperature, solar radiation, and wind speed show a positive correlation with changes in water profit and loss, while precipitation shows a negative correlation[49]. We compare our results on the water deficit situation in the Yanhe River Basin with previous researches. These results are consistent with the results on the factors influencing moisture profit and loss in the Yanhe River basin, precipitation was the meteorological factor with the most significant influence on the drought situation. The study area is located in the semi-arid region of northwestern China, with low annual precipitation. The seasonal distribution of precipitation is uneven, and rain mostly occurs from June to September. In recent years, the amount of precipitation has decreased [50], especially in spring, summer, and autumn [2]. Hence, the water resources in the Yanhe River basin have been minimized. Under the influence of this factor, the water deficit situation in the Yanhe River Basin is becoming more and more severe.

 

Section 5.2 gives three reasons for the water deficit in the basin. However, I think only the first one can be supported by this study for three reasons: (1) the water deficit is identified by MPLD in this study; (2) this paper never mentions the effects of vegetation on MPLD, thus it is not reasonable to infer the vegetation restoration effects on MPLD; and (3) similarly, this paper never mentions how economic development and population growth affect farmland moisture.

Response: Thank you for your careful review. Following your suggestion, we have removed the impact of the vegetation you mentioned on MPLD and the impact of economic development and population growth on MPLD.

 

In the paper, remote sensing data, model derived data, and site observed data were used. However, they are in different spatial and temporal resolution. Please add additional discussion on the uncertainty of this study.

Response: Thank you for your careful review. Following your suggestion, we added a discussion about research uncertainty. The revisions can be found in the subsection 5.

5.4. Uncertainty of this study

The Uncertainty of this study mainly come from three aspects, one is the error that ET0 calculation process may cause, the other is the error of the ET data product used, and the third is the error caused by the interpolation of meteorological data. The ET0 calculation error is mainly due to the uncertainty of the model and the uncertainty of the input parameters. The calculation process of ET0 is complicated and is greatly affected by meteorological data, land cover type and soil properties. Therefore, it must be simplified in the actual calculation process, which may lead to equation calculation errors. The second uncertainty of ET0 calculation is derived from the error of the input parameters. The data used for parameter estimation is mostly obtained by data measurement. Instrument faults, different spatial and temporal resolutions, etc. during the measurement process may cause data errors [52]. As calculated in the Penman-Monteith model for the net radiation (Rn) parameter, the net radiation (Rn) is the difference between the net solar radiation (Rns) and (Rnl). Since solar radiation is determined by factors such as solar constant, sun dip, geographical position and atmospheric transmittance, and ground height [42], some of the parameters used in the calculation of this parameter are applicable globally, and may be applied to small areas. Bring some error. Studies have shown that the relative error of Rs calculated based on existing remote sensing or at flux tower sites data is about 10% [53,54]. The ET data used in this study was calculated using the SSEBop model, which simplifies the surface energy balance equation and does not explicitly solve the sensible heat flux and geothermal flux. The simplification of the SSEBop model leads to certain uncertainties in the model output process [55]. Second is the model output error due to the uncertainty of the input variable error. If studies show that under stable atmospheric conditions, the Ts error of all stations is generally within 1k [56]. However, in semi-arid and arid regions, the error may be as high as 5k due to emissivity and albedo [38]. The error about meteorological data mainly comes from interpolation, and the difference in the interpolation method used will inevitably bring some errors.In this study, we used AUSPLIN to interpolate meteorological data. In the interpolation process, we added the consideration of topographical factors, which minimized the occurrence of errors.

 

Line 186 Section 3.1 I think average temperature should be air temperature.

Response: Thank you very much for your correction. We apologize for this mistake. We have changed the average temperature to air temperature. The revisions can be found in subsection 3.

 

Line 345 How did you get table 1, please add more explanations on it.

Response: Thank you for your careful review. First of all, based on the area of each water surplus and loss in 2003-2015, we obtained the proportion of the area of each water surplus. Secondly, we subtracted the area of each water surplus and loss in 2015 from the area of water surplus and loss in 2003, and obtained the change in the degree of water surplus and loss in 2003-2015. Finally, the rate of change in 2003-2015 is the ratio of the area of water surplus and loss in 2003 to the change in the degree of water surplus and loss in 2003-2015.

 

Line 243 I did not find the temporal resolution of your calculated MPLD, yearly?

Response: Thank you very much for your reminder. We are apologize that we did not indicate the time resolution of MPLD. This study calculates the time resolution of MPLD for each year. The revisions can be found in the subsection 3.

 

Line 388 From figure 3, it is difficult to draw any conclusion on the trend of MPLD. The water shortage trend is also not clear. For example, the Acute percentages were very small from year 2009 to 2014 comparing to year 2004-2008.

Response: Thank you for your careful review. Following your suggestion, we calculated the trend of each grid unit. The revisions can be found in the subsection 4 .

4.1.3. Variation trend of moisture profit and loss degree

In order to more clearly show the trend of MPLD in 2003-2015, we calculated the trend of each grid unit(Fig. 4). We can see that from 2003 to 2015, the water deficit in the upper and lower reaches of the Yanhe River Basin showed an intensifying trend, and the water deficit situation in the Yan River Basin was weakened.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors well addressed the reviewer's comments, it is now acceptable for publication.

Author Response

Dear editors and reviewers,

    Thank you again for your letter and for the reviewers’ comments regarding our manuscript entitled “Spatio-Temporal Variations in Farmland Water Conditions in the Yanhe River Basin” (ID: water-579390). These comments were valuable and very helpful for revising and improving our paper. We have studied the comments carefully and have made corrections, which we hope meet with your approval. The main corrections made to the paper and the response to the reviewer’s comments are as follows:

Reviewers' comments:

Reviewer #3:

 

Major comments:

The scientific creativity of this paper is really unclear. From my view, this manuscript is still a project report but not journal paper.

Response: Thank you for your careful review. Following your suggestion, we made a lot of changes to clarify the scientific creativity of the manuscript. The revisions can be found in the first and second paragraphs in subsection 1 (Introduction).  

We believe that the scientific creativity of the paper can be found in the followed three aspects:

（1）The importance of moisture profit and loss research。Drought is a natural disaster with a high frequency of occurrence, which will have long-term adverse effects on regional agricultural production, social and economic development, and the ecological environment. As the stages of crop growth depend on water resources and soil moisture, drought has a greater impact on the agricultural sector. Indicators for characterizing dry and wet conditions include precipitation, dryness, and water surplus and loss, while water deficits take into account the combined effects of precipitation and evaporation. In this study, we analyze the climate drought situation in the Yanhe River Basin from the study of water surplus and loss in this region.

（2）The particularity of the study area. China is one of the most arid countries in the world, with arid and semi-arid areas accounting for half of the total area and mainly concentrated in the northwest. The Yanhe River Basin is a typical semi-arid area in China. The agriculture in the basin is very developed, but the climatic conditions in the basin limited the agricultural development due to water shortage. Therefore, we believe that the discussion on the water surplus and loss of cultivated land in the Yanhe River Basin will help the management of water resources in the basin, and also provide advice on agricultural development in other semi-arid regions of the world.

（3）Key points of this paper

In this study, we adopted the moisture profit and loss degree index model to analyze moisture profit and loss situation and changes, characteristics of moisture profit and loss transition, variation trend of moisture profit and loss degree, and spatial distribution of moisture profit and loss in the Yanhe River basin from 2003 to 2015. We explored the influences of climate factors on farmland moisture profits and losses in the Yanhe River basin via correlation analysis. We also further analyzed changes in impact factors in different years and spatial performance of impact factors on MPLD.

 

The language needs to be improved, as we can find some gamma errors, such as line 220, line 306-309, line 425-451

Response: Thank you for your careful review. We are sorry for the mistakes in language. In the revised version, we hired a native speaker to help use improve the language.

Author Response File: Author Response.pdf

Reviewer 3 Report

Review of the paper “Spatial-Temporal Variations in Farmland Water Conditions in the Yanhe River Basin” by Wang et al. submitted to water.

General comments:

This is my second reviewing this manuscript. The authors have added additonal detailed information on this study. However, as I mentioned previously, the scientific creativity of this paper is really unclear. From my view, this manuscript is still a project report but not journal paper.  

 

General comments:

1. The language needs to be improved, as we can find some gamma errors, such as line 220, line 306-309, line 425-451

Author Response

Dear editors and reviewers,

    Thank you again for your letter and for the reviewers’ comments regarding our manuscript entitled “Spatio-Temporal Variations in Farmland Water Conditions in the Yanhe River Basin” (ID: water-579390). These comments were valuable and very helpful for revising and improving our paper. We have studied the comments carefully and have made corrections, which we hope meet with your approval. The main corrections made to the paper and the response to the reviewer’s comments are as follows:

Reviewers' comments:

Reviewer #3:

 

Major comments:

The scientific creativity of this paper is really unclear. From my view, this manuscript is still a project report but not journal paper.

Response: Thank you for your careful review. Following your suggestion, we made a lot of changes to clarify the scientific creativity of the manuscript. The revisions can be found in the first and second paragraphs in subsection 1 (Introduction).  

We believe that the scientific creativity of the paper can be found in the followed three aspects:

（1）The importance of moisture profit and loss research。Drought is a natural disaster with a high frequency of occurrence, which will have long-term adverse effects on regional agricultural production, social and economic development, and the ecological environment. As the stages of crop growth depend on water resources and soil moisture, drought has a greater impact on the agricultural sector. Indicators for characterizing dry and wet conditions include precipitation, dryness, and water surplus and loss, while water deficits take into account the combined effects of precipitation and evaporation. In this study, we analyze the climate drought situation in the Yanhe River Basin from the study of water surplus and loss in this region.

（2）The particularity of the study area. China is one of the most arid countries in the world, with arid and semi-arid areas accounting for half of the total area and mainly concentrated in the northwest. The Yanhe River Basin is a typical semi-arid area in China. The agriculture in the basin is very developed, but the climatic conditions in the basin limited the agricultural development due to water shortage. Therefore, we believe that the discussion on the water surplus and loss of cultivated land in the Yanhe River Basin will help the management of water resources in the basin, and also provide advice on agricultural development in other semi-arid regions of the world.

（3）Key points of this paper

In this study, we adopted the moisture profit and loss degree index model to analyze moisture profit and loss situation and changes, characteristics of moisture profit and loss transition, variation trend of moisture profit and loss degree, and spatial distribution of moisture profit and loss in the Yanhe River basin from 2003 to 2015. We explored the influences of climate factors on farmland moisture profits and losses in the Yanhe River basin via correlation analysis. We also further analyzed changes in impact factors in different years and spatial performance of impact factors on MPLD.

 

The language needs to be improved, as we can find some gamma errors, such as line 220, line 306-309, line 425-451

Response: Thank you for your careful review. We are sorry for the mistakes in language. In the revised version, we hired a native speaker to help use improve the language.

Author Response File: Author Response.pdf