The Analysis of Long-Term Trends in the Meteorological and Hydrological Drought Occurrences Using Non-Parametric Methods—Case Study of the Catchment of the Upper Noteć River (Central Poland)

Round 1

Reviewer 1 Report

General Comments: This study analyzed trend in meteorological and hydrological drought in the Upper Notec River basin. The trend analysis was carried out at 8 meteorological stations and hydrological stations using Mann-Kendal’s test and Sen’s slope test. Finally, the correlation analysis between SPI and SRI was performed.

Reviews:

Overall, this topic is good. But I have several concerns about this study. Authors are advised to address all the concerns briefly before resubmission. My recommendation is Major revision.

Comments:

1. The contribution of this study is not novel, I recommend authors to highlight the novelty of this study clearly in the introduction section. It is not a new contribution in the research. It’s better to change its title to a case study.
2. Authors are advised to improve the introduction section by citing latest studies on drought such as:

Kim, T. W., & Jehanzaib, M. (2020). Drought risk analysis, forecasting and assessment under climate change.

3. Line 85: There sentence structure is not clear.
4. Line 86-87: Is it average annual precipitation? It is better to use average precipitation (lowest and highest) for the study period 1981-2016 rather than 1981-2010.
5. Figure 1: Revise figure 1(b) and change the colors of DEM for clarity. This figure is not clearly elaborating the elevation.
6. Table 1: Caption should be Annual sum instead of sums.
7. Table 1: Symbols of degree and minutes should be added with Latitude and Longitude.
8. In Figure 2: Revise y-axis titles with full names of parameters and add x-axis title.
9. How authors calculated the SPI at 3-, 6-, 9- and 12-month timescale? Which probability distribution was employed for the calculation of SPI?
10. Table 3: Revise table 3, replace comma in between SPI and SRI with "/".
11. Sub-section 2.3: It is necessary to perform pre-whitening test to the data before the application of Mann-Kendal test. There is no explanation about pre-whitening process.
12. Sub-section 2.3: Mann-Kendal test: Z>1.96. Replace all the comma's with dot in Z values.
13. Previous studies also performed Sen's slope test, Mann-Kendal test and correlation analysis for drought analysis. Authors are advised to compare the results of this study with these previous studies.

Jehanzaib, M., & Kim, T. W. (2020). Exploring the influence of climate change-induced drought propagation on wetlands. Ecological Engineering, 149, 105799.

Jehanzaib, M., Shah, S. A., Kwon, H. H., & Kim, T. W. (2020). Investigating the influence of natural events and anthropogenic activities on hydrological drought in South Korea.   Terrestrial, Atmospheric & Oceanic Sciences, 31(1).

Jehanzaib, M., Sattar, M. N., Lee, J. H., & Kim, T. W. (2020). Investigating effect of climate change on drought propagation from meteorological to hydrological drought using multi-model ensemble projections. Stochastic Environmental Research and Risk Assessment,   34(1), 7-21.

14. Figure 3: a) Why there is no significant trend at SPI one month timescale while there is significant trend observed at other accumulation periods. Spellings of legend are wrong.
15. Revise Figure 4: Axis titles (x and y) must be provided in each Figure. The name of station should not be removed from SRI. Find other place for station name.
16. Figure 5: Axis titles must be provided.
17. This manuscript has many grammatical mistakes. Revise the manuscript with the aid of native English speaker

Author Response

The answers in the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper highlighted the hydrological and meteorological drought analysis using different drought indices at different time scales and their relationship in the upper Noteć catchment. I am suggesting the following specific minor revisions:

1. Section 2.1, Line 85 check “ther”.
2. Figure 1: To make the figure more understandable, the authors should improve it by including:

• North arrow indicator
• Remove river/stream networks outside the study area boundary.
• Figure legend source: correct Table 2 to Table 1.

3. Table 1: units used for altitude, latitude and longitude shall be given.
4. Figure 2: Define the abbreviations P and T used in the figure legend.
5. Section 2.2 line 160-162 the authors indicated that 5 meteorological stations (Izbica Kujawska, Strzelno, Kołuda Wielka, Sompolno and Pakość) were used to evaluate the SPI, which contradicts the 8 stations you discussed throughout the paper.
6. Section 3.1 Check the time period used for drought analysis and make it consistent throughout the paper: is it 1980-2016 or 1981-2016?
7. Line 263, check whether the hydrological drought you want to specify here is or .
8. Figure 4: The authors took the average SPI of 8 meteorological stations and compared it with the SRI at the main outlet of the catchment (Pakość), giving equal weight to each station, but the stations are not evenly distributed over the catchment (Fig. 1). Therefore, to be realistic, the authors should first convert point precipitation to areal precipitation over the catchment, e.g., using the Thiessen polygon, and then calculate the SPI and compare the result with SRI.
9. Table 6: To make the table more understandable, authors should:

• Use the same decimal place and scientific notation for all small and large number i.e., 8.99 x 10⁶, 6.92 x 10^-2
• Align parameters (Z, S...) and their value for different SPI time scales along a straight line in the table.
• In the table, use the same natation in the table as defined in the method section, otherwise define in the table heading.

10. Section 3.3 and figure 5: It is not clear which meteorological station SPI was compared to SRI? See also comment #8 here. In figure 5 axis titles should be added and grids removed.

Comments for author File: Comments.pdf

Author Response

The answer in the attachment

Author Response File: Author Response.docx

Reviewer 3 Report

Based on the estimation of standardized precipitation index (SPI) and standardized runoff index (SRI), this study investigates the variability and correlation of hydrological drought and meteorological drought in the catchment area of the Upper Notec river, which covers an agricultural area of Poland with some of the lowest water reserves.

Trend analysis is carried out using Mann Kendal Test and Sen’s slope method.

The results showed that statistically significant trends were identified at 3 out of 8 meteorological stations (downward trend at one station and upward trend for drought at 2 stations). As far as hydrological droughts are concerned, a statistically significant upward trend is observed at one station, one significant downward trend is noted at one station and no trend was found at one station.

In the opinion of the reviewer, the submitted manuscript may hold the potential to be suitable for publication in Atmosphere subject to several recommended modifications.

Line 14 Abstract

The case study focuses on the catchment of the Upper Notec river, which is a heavily exploited agricultural area with some of the lowest reserves of water. The authors should convince the readers that the paper can be original, and valuable contribution not to a particular region only.

Line 97 Fig.1

Where is the Notec River?

Line 143 Fig.2

Why is the average annual air temperature represented as continuous line and average precipitation sums as a bar graph?

Line 163

Short definition of SPI could be helpful

Line 169

Why f is not defined. f is different for precipitation and discharge

Line 178

Wrong reference

Line 179

How are determined the parameters of the logarithmic function

Line 188, Table 3

the classification scale is not defined properly (semi-infinitive intervals)

Line 220 Section 2.5

The use of the Pearson correlation coefficient requires a fundamental assumption that random variables under investigation (SPI and SRI) are linearly dependent. However, the assumption regarding the inherently linear dependence is challenged in the Rainfall-Runoff hydrological system.

Therefore, the Pearson correlation analysis may be not well suitable for dealing with highly nonlinear relationships between SPI and SRI.

For the current study, ignoring the nonlinear dependence of the SPI on the SRI can lead to the inaccurate drought response time.

Line 270

Should these two station be excluded from the section 2.5 because of anthropogenic activities carried out in the area?

Line 303, Fig.4

Fig.4 (and Fig.5) is wrong.

Please note, that SPI is calculated in the following sequence. A monthly precipitation data set is prepared for a period of 432 months.

A set of averaging periods are selected to determine a set of time scales of period i=1,3,6,9,12 months. These represent arbitrary but typical time scales for precipitation deficits. The data set is moving in the sense that each month a new value is determined from the previous i months. So, how was calculated SPI-12 (and correlation coefficient) for 1981?

Line 324, Table 6 and Table 7

Three significant figures could be enough, e.g., 8.99e+06 not 8.988927e+06, and used everywhere.

Table could be simplified to Z, and Sen’s slope. The authors do not refer to S, var_S and p-value is related to Z.

Line 341, 3.3. Correlations between SPI and SRI values

Figure 5 displays the comparisons of SPI and SRI for the five different timescales (1, 3, 6, 9, and 12 months) for the years 1981–2020. Fluctuation and variation of SPI and SRI series show consistent patterns over the study period. However, it looks like the degree of consistency changes with timescales.

The statistical result should reveal that the correlations between SPI and SRI drop from the value calculated for the 12-month timescale to the values calculated for the 9-, 6-, 3-, and 1-month timescales, indicating that the differences between the two indices increase as timescale decreases.

Line 347

In the case of individual years, the correlation indicators between hydrological and meteorological droughts are rather misleading. The highest correlation is about 0.94 and the lowest -0.9. What does it mean for decision makers?

I would suggest removing Fig.5 and examining the relationship between  1-month SRI and SPI at different Timescales (1,2,3,4..)

Due to hydrologic detention of subsurface soil moisture, shallow groundwater and perhaps reservoir storage, a 2-month timescale of SPI could be more appropriate for river discharge monitoring.

Line 389

As an increase in air temperature in the analysed area is an additional element (Fig. 2) which leads to an increase in evapotranspiration why the standardized precipitation–evapotranspiration index SPEI is not considered?

If the catchment area of the Upper Notec river requires using several indicators in order to assess the actual condition of the water reserves, why the authors limited the research to only 2 indicators. The following indices could be examined: Precipitation Concentration Index (PCI), Seasonality Index (SI), and Rainfall Anomaly Index (RAI).

Comments for author File: Comments.pdf

Author Response

The answer in the attachment

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Round 2

Reviewer 1 Report

Manuscript Title: The analysis of long-term trends in the meteorological and hydrological drought occurrences using non-parametric methods – case study of the catchment of the Upper Noteć river (central Poland) Manuscript ID: atmosphere-1322430 General Comments: This study analyzed trend in meteorological and hydrological drought in the Upper Notec River basin. The trend analysis was carried out at 8 meteorological stations and hydrological stations using Mann-Kendal’s test and Sen’s slope test. Finally, the correlation analysis between SPI and SRI was performed. Reviews: Authors significantly improved the manuscript. My decision is to "Accept" the manuscript after these minor changes. Comments: 1. Revise the Legend of Figure 1: Replace "station" with "stations". 2. Figure 2: Change the x-axis and y-axis title to "Precipitation (mm)" and "Year", respectively. 3. Replace x-axis title (Years) of Figure 4 & 5 with "Year". 4. Table 7: Remove blank colored rows present on top of Table 7 or adjust table according to the color as presented in the first version of manuscript. 5. Table 6: Remove blank colored rows present on top of Table 6 or adjust table according to the color as presented in the first version of manuscript.

Author Response

Review 1

Manuscript Title: The analysis of long-term trends in the meteorological and hydrological drought occurrences using non-parametric methods – case study of the catchment of the Upper Noteć river (central Poland) Manuscript ID: atmosphere-1322430 General Comments: This study analyzed trend in meteorological and hydrological drought in the Upper Notec River basin. The trend analysis was carried out at 8 meteorological stations and hydrological stations using Mann-Kendal’s test and Sen’s slope test. Finally, the correlation analysis between SPI and SRI was performed. Reviews: Authors significantly improved the manuscript. My decision is to "Accept" the manuscript after these minor changes. Comments: 1. Revise the Legend of Figure 1: Replace "station" with "stations".

- we corrected

2. Figure 2: Change the x-axis and y-axis title to "Precipitation (mm)" and "Year", respectively.

- we corrected

3. Replace x-axis title (Years) of Figure 4 & 5 with "Year".

- we corrected

4. Table 7: Remove blank colored rows present on top of Table 7 or adjust table according to the color as presented in the first version of manuscript.

- we corrected

5. Table 6: Remove blank colored rows present on top of Table 6 or adjust table according to the color as presented in the first version of manuscript.

- we corrected

 

We thank you for your comments

Author Response File: Author Response.docx

Reviewer 3 Report

the classification scale is not defined properly (semi-infinitive intervals)
The SPI and SRI ranges are correct. They are consistent with the literature on the subject. ..but wrong from the matematical point of view and not consistent with:

Thomas B. McKee, Nolan J. Doesken and John Kleist, THE RELATIONSHIP OF DROUGHT FREQUENCY AND DURATION TO TIME SCALES, Eighth Conference on Applied Climatology, 17-22 January 1993, Anaheim, California

 

.... the Pearson correlation analysis may be not well suitable for dealing with highly nonlinear relationships between SPI and SRI. For the current study, ignoring the nonlinear dependence of the SPI on the SRI can lead to the inaccurate drought response time.
The proposed method was used by many authors. It presents a simple relationship between SPI and SRI,
This is not the answer to my question!

Author Response

the classification scale is not defined properly (semi-infinitive intervals)
The SPI and SRI ranges are correct. They are consistent with the literature on the subject. ..but wrong from the matematical point of view and not consistent with:

Thomas B. McKee, Nolan J. Doesken and John Kleist, THE RELATIONSHIP OF DROUGHT FREQUENCY AND DURATION TO TIME SCALES, Eighth Conference on Applied Climatology, 17-22 January 1993, Anaheim, California

- we have removed the reference to Mc Kee et al.in line 186. The classification of droughts is presented in table 3. As we mentioned earlier, we applied a scale adopted and used by other authors.In our opinion, it is the most legible way of recording drought intervals.

.... the Pearson correlation analysis may be not well suitable for dealing with highly nonlinear relationships between SPI and SRI. For the current study, ignoring the nonlinear dependence of the SPI on the SRI can lead to the inaccurate drought response time.
The proposed method was used by many authors. It presents a simple relationship between SPI and SRI,
This is not the answer to my question!

- so far, there have been no studies on the relationship between SPI and SRI for the Noteć catchment area. Our research is the first to implement such a relationship for the upper catchment area of the Noteć. The area is specific because for this catchment many other anthropogenic factors influence the size of the flows. We were not sure if the relationship between meteorological and hydrological droughts would be visible, so we first used the simple Pearson correlation.

- We are aware that the results obtained in the Perason correlation analysis should not be directly interpreted. We highlighted this in the article in the discussion section:

“In the case of the catchment area of ​​the Upper Noteć river, the relationships between meteorological and hydrological conditions are not natural. The flow regime depends on the amount of water discharged in particular periods and on the retention capacity of lakes, which is particularly noticeable at the Pakość station. The amount of water accumulated in the Pakość reservoir, which the Noteć flows through, is regulated by a water accumulating weir”.

The obtained results indicate that further studies are required that will concern the relationship between droughts and will take into account non-linear relationships.

Thank you for your comments.

Author Response File: Author Response.docx