Meteorological and Hydrological Drought Analysis and Its Impact on Water Quality and Stream Integrity
Round 1
Reviewer 1 Report
Meteorological and hydrological drought were evaluated by SPI and SSI, their relations to water quality and stream integrity were analyzed in the Raritan Basin. The results indicated SPI and SSI were able to identify drought events, and it wud be an interesting contribution to the literature of drought assessment in the basin level.
- Equation (3)- (10) can be removed, only the references were necessary, because these methods are popular and familiar for the readers.
- Please make the Fig. 2-6 more clear.
Author Response
Responses to Reviewers 1’ Comments
We appreciate the constructive comments from Reviewer, which were carefully assessed and taken into consideration in our revision. The reviewers’ original comments are in bold and our responses are in regular font.
Reviewer#1:
Q-1: Equation (3)- (10) can be removed, only the references were necessary, because these methods are popular and familiar for the readers.
Response: Based on reviewer’s suggestion, we have removed the equations from 3 to 10 in the revised manuscript.
Q-2: Please make the Fig. 2-6 more clear.
Response: As 1-month and 3-months temporal pattern looks similar, we removed the figure corresponding to 3 month from Figure 2 to Figures 6. Now, it looks much more clear. This changes can be found in the current Figures(2 to 6) in the revised manuscript.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
There should be a comprehensive literature review on
#1. Review recent studies on the observed drought trends.
#2. Review studies on the projected changes in precipitation, warming, and drought over the region. And discuss the implications of your findings concerning the projected changes of drought over the study region. L109-111 is not clear. The word “Intensifying hydrological cycle” is vague.
#3 L113-114: Review of previous regional and global studies on the effect of drought on water quality and stream integrity.
Other comments
#4 There should be a well-balanced discussion on the strength/weakness of drought indices. L61-65 very lengthy (unnecessary) discussion. The literature review should be very brief and to the point.
#5 L59-60: I suggest the authors discuss why these indices are suitable for this study. Compare/contrast the drought indices in relation to the purpose of your study.
#6 L177-178; what about standardized precipitation evapotranspiration index (SPEI)?
L109-111: the authors mentioned that temperature is projected to increase over the basin. SPI can’t explain drought severity due to enhanced warming.
Author Response
Responses to Reviewers 2’ Comments
We appreciate the constructive comments from Reviewer, which were carefully assessed and taken into consideration in our revision. The reviewers’ original comments are in bold and our responses are in regular font.
Reviewer#2:
There should be a comprehensive literature review on
Q-1: Review recent studies on the observed drought trends.
Response: Based on reviewer’s suggestion, we have added the observed drought trends of recent studies in the 1st paragraph of the revised manuscript and also provided below:
“The increase in global temperature has altered the spatiotemporal pattern of drought events [8]. Using satellite based combined moisture-thermal condition index, Kogan et al.[9] pointed out that world drought area increased approximately 2 to 5% for all intensities including severe to exceptional, extreme to exceptional, and exceptional categories during 1998 to 2014 due to intensification of global warming. McCabe and Wolock [10] observed that roughly 2% of global land area were in drought throughout all the years since 1901 to 2009 using month-by-month potential evapotranspiration and long term mean monthly precipitation data. This study results depicted a statistically significant positive drought trend at a 95% confidence level. Additionally, Song et al. [11] demonstrated that the secure trend of meteorological drought index changed from -0.001 in 1950 to -0.383 during 2014, indicating an increasing global drought trends.”
References:
- Mukherjee, S., Mishra, A. K., 2021. Increase in compound drought and heatwaves in a warming world. Geophysical Research Letters, 48, e2020GL090617. https://doi. org/10.1029/2020GL090617.
- Kogan, F., Guo, W., Yang, W., 2020. Near 40 years drought trend during 1981-2019 earth warming and food security. Geomatics Natural Hazards and Risks 11, 469-490.
- McCabe, G., Wolock, D.M., 2015. Variability and trends in global drought. Earth and Space Science 2, 223-228.
- Song, X., Song, Y., Chen, Y., 2020. Secular trends of flobal drought since 1950. Environmental Research Letters 15, 094073.
Q-2: Review studies on the projected changes in precipitation, warming, and drought over the region. And discuss the implications of your findings concerning the projected changes of drought over the study region. L109-111 is not clear. The word “Intensifying hydrological cycle” is vague.
Response: We have incorporated literature review on precipitation and temperature projection in the region in the revised manuscript (2nd paragrapgh, page #3) as well as presented below.
“Furthermore, a recent study in the basin suggested that the annual temperature in the basin likely to increase by 33.3% and 35.7% by 2045 for moderate greenhouse gas emmision scenario and extreme greenhouse emission scenario, respectively while the projected precipitation expected to slightly decrease (3.5% to 4.0%) in the basin[38]. The projected increased temperature combined with decreased precpitation and associated evapotranspiration may lead to increased drought occurance and severity in the basin.”
Regarding drought in the region: Below sentences which reflect the drought condition in the study region are already presented in the manuscript.
“New Jersey has experienced several droughts of varying degree since 1950 which resulted into shortage of water. The most severe droughts were observed during mid-1960, early to mid-1980, and in 2001-2002 whilst drought watch was declared for short period of time during 2005, 2006, 2010, 2015, and 2016-2017 (NJDEP, 2017)”.
P.S: Please note that none of the study has projected the fututre drought condition in the basin.
References:
- Giri, S., Arbab, N.N., Lathrop, R.G., 2019. Assessing the potential impacts of climate and land use change on water fluxes and sediment transport in a loosely coupled system. Journal of Hydrology 577, 123955.
- New Jersey Department of Environmental Protection (NJDEP), 2017. New Jersey Water supply plan 2017-2022: 484p, Available at: http://www.nj.gov/dep/watersupply/wsp.html.
Q-3: Review of previous regional and global studies on the effect of drought on water quality and stream integrity.
Response: We have incorporated literature review on the effect of drought on water quality and stream integrity in the revised manuscript (3rd paragrapgh, page #3) as well as provided below:
Few researchers have looked at the impacts of drought on water quality and stream integrity [39-43]. For example, Pena-Guerrero et al. [40] evaluated the potential impacts of hydrological drought on water quality using SSI in the Maipo River Basin in the central Chile. The study results found a significant negative relationship of hydrological drought to several water quality parameters including PH, electrical conductivity, sodium, magnesium, calcium, nitrate, and phosphate. Mosley [41] found that nutrients and turbidity decreased during droughts in rivers and streams due to insignificant loadings from different pollution sources. Furthermore, the potential effects of drought on water quality was assessed in the Meuse River, western Europe and pointed out that the deterioration of water quality including eutrophication, major elements, heavy metals and metalloids was observed during drought periods [42]. Herbst et al. [43] evaluated the impacts of drought on benthic macroinvertebrate communities in 12 mountainous streams in Sierra Neveda and California. This study highlighted that macroinvertebrate community structure, diversity, and ecosystem function on small headwater streams are more vulnerable to droughts.
References:
- Mishra, A., Alnahit, A., Campbell, B.,2021. Impact of land uses, drought, flood, wildfire, and cascading events on water quality and microbial communities: a review and analysis, Journal of Hydrology, 125707.
- Pena-Guerrero, M.D., Nauditt, A., Munoz-Robles, C., Ribbe, L., Meza, F., 2020. Drought impacts on water quality and potential implications for agricultural production in the Maipo River Basin, Central Chile. Hydrological Sciences Journal 65, 1005-1021.
41.Mosley, L.M., 2015. Drought impacts on the water quality of freshwater systems; review and integration. Earth Science Reviews 140, 203-214.
- Van Vliet, M.T.H., Zwolsman, J.J.G., 2008. Impact of summer droughts on the water quality of the Meuse river. Journal of Hydrology 353, 1-17.
- Herbst, D.B., Cooper, S.D., Medhurst, R.B., Wiseman, S.W., Hunsaker, C.T., 2019. Drought ecohydrology alters the structure and function of benthic invertebrate communities in mountaneous streams. Freshwater Biology 1-17, DOI: 10.1111/fwb.13270.
Other comments:
Q-4: There should be a well-balanced discussion on the strength/weakness of drought indices. L61-65 very lengthy (unnecessary) discussion. The literature review should be very brief and to the point.
Response: Based on the reccomendation, we have incorporated both strength and weakness of SPI and SSI in the revised manuscript (1st paragraph, page#3) and also provided below:
“SPI and SSI are selected due to their simplicity of calculation, easy to understand, comparability, and flexibility of user-defined accumulation periods concurrent with endorsement by the World Meteorological Organization [27,31].
Q-5: L59-60: I suggest the authors discuss why these indices are suitable for this study. Compare/contrast the drought indices in relation to the purpose of your study.
Response: Based on the recommendation, we have incorporated following in the revised manuscript (2nd paragraph, page#2).
“Out of all drought indices, SPI and SSI are selected for drought analysis in this study as both drought indices can be calculated for variety of accumulation periods(i.e. 1-month, 3-months, 6-months, and 12-months) which facilitates to investigate the impacts of drought not only from agricultural production point of view but also from water supply prospective in the region. Agricultural production is related to availability of soil moisture which is the reflection of precipitation anomalies in the shorter accumualtion period such as 1-month. Additionally, water supply to urban areas depends on water availability in the streams and rivers which is the reflection of longer accumulation precipitation anomalies including 6-months and 12-months. Therefore, use of these drought indices will help us formulate better water resources management policies from both agricultural production as well as water supply prospective in the study area. “
Q-6: L177-178; what about standardized precipitation evapotranspiration index (SPEI)? L109-111: the authors mentioned that temperature is projected to increase over the basin. SPI can’t explain drought severity due to enhanced warming.
Response: We agree with the reviewer that SPI can not incorporate the temperature factor while estimating drought indices. On the other hand, standardized precipitation and evapotranspiration index (SPEI) incorporates both precipitation and evapotranspiration during drought estimation. However, we have used streamflow for calculating SSI (standardized streamflow index). The evapotranspiration componet is accounted in the streamflow which can compensate the limitation of SPI.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
#1 L90-100: cite Aryal and Zhu (2017)
Aryal, Y., & Zhu, J. (2017). On bias correction in drought frequency analysis based on climate models. Climatic Change, 140(3-4), 361-374.
# 2 (comment in my previous review: what about standardized precipitation evapotranspiration index (SPEI)? L109-111: the authors mentioned that temperature is projected to increase over the basin. SPI can’t explain drought severity due to enhanced warming.)
Discuss the implication of this study in relation to projected changes in meteorological drought (SPI) and streamflow drought (SSI). Projected changes in SSI can’t be inferred by projected changes in SPI (SPEI might be a better predictor of SSI because it incorporates evaporative part).
#3 In Abstract/conclusion: Can we generalize the findings/conclusion from this study to infer (may be qualitatively) to infer the role of drought on Water Quality/Stream Integrity in other regions with similar climates or similar land use etc? Please mention/discuss.
Author Response
Responses to Reviewers 2’ Comments
We appreciate the constructive comments from Reviewer, which were carefully assessed and taken into consideration in our revision. The reviewers’ original comments are in bold and our responses are in regular font.
Q-1: L90-100: cite Aryal and Zhu (2017)
Aryal, Y., & Zhu, J. (2017). On bias correction in drought frequency analysis based on climate models. Climatic Change, 140(3-4), 361-374.
Response: Based on reviewer’s suggestion, we have incorporated the above reference in the revised manuscript between L 90-100.
Q-2: (comment in my previous review: what about standardized precipitation evapotranspiration index (SPEI)? L109-111: the authors mentioned that temperature is projected to increase over the basin. SPI can’t explain drought severity due to enhanced warming.)
Discuss the implication of this study in relation to projected changes in meteorological drought (SPI) and streamflow drought (SSI). Projected changes in SSI can’t be inferred by projected changes in SPI (SPEI might be a better predictor of SSI because it incorporates evaporative part).
Response: “The shift in hydrologic cycle components (e.g., rainfall, temperature) can trigger droughts. To quantify drought events, different drought indices are derived, for example, SPI based on precipitation and SPEI based on precipitation and evapotranspiration. The SPEI can be a better indicator for climate change assessment as it incorporates evapotranspiration (controlled by temperature) for drought assessment. Besides SPEI, the SSI can be considered as an indicator for climate change assessment as the streamflow is a cumulative effect of precipitation and temperature. Therefore, we used SSI in our study for the streamflow drought assessment. In future studies, we will perform a comprehensive analysis by evaluating individual and multivariate drought indexes.”
Q-3: In Abstract/conclusion: Can we generalize the findings/conclusion from this study to infer (may be qualitatively) to infer the role of drought on Water Quality/Stream Integrity in other regions with similar climates or similar land use etc? Please mention/discuss.
Response: Based on reviewer’s suggestion, we have incorporated the findings of water quality/stream integrity in a more generalized form in the Abstract as well as presented below.
“The average pollutant concentration of drought periods were lesser than non-drought periods due to reduction of different processes such as erosion and transport of sediment and nutrients into rivers and streams during drought periods as opposed to non-drought periods.”
Round 3
Reviewer 2 Report
The authors have addressed review comments thoroughly/properly. Now I recommend publication.
