the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Drought cascades across multiple systems in Central Asia identified based on the dynamic space-time motion approach
Lu Tian
Markus Disse
Jingshui Huang
Abstract. Drought is typically induced by the extreme water deficit stress that cascades through the atmosphere, hydrosphere, and biosphere. Cascading drought events could cause severe damage in multiple systems. However, identifying cascading drought connections considering the dynamic space-time progression remains challenging, which hinders further exploring the emergent patterns of drought cascades. This study proposes a novel framework for tracking drought cascades across multiple systems by utilizing dynamic space-time motion similarities. Our investigation focuses on the four primary drought types in Central Asia from 1980 to 2007, namely precipitation (PCP), evapotranspiration (ET), runoff, and root-zone soil moisture (SM), representing the four systems of atmosphere, hydrosphere, biosphere, and soil layer respectively. 503 cascading drought events are identified in this study, including the 261 four-system cascading drought events. Our results show a significant prevalence of the four-system cascading drought pattern in Central Asia with high systematic drought risk, mainly when seasonal PCP droughts with high severity/intensity and sizeable spatial extent are observed. As for the temporal order in the cascading drought events, ET droughts are likely to occur earlier than Runoff droughts after PCP droughts, and SM droughts are more likely to occur at last, implying the integrated driven effect of the energy-limited and water-limited phases on the drought progression in Central Asia. Our proposed framework could attain precise internal spatial trajectories within each cascading drought event and enable the capture of space-time cascading connections across diverse drought systems and associated hazards. The identification of cascading drought patterns could provide a systematic understanding of the drought evolution across multiple systems under exacerbated global warming.
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Lu Tian et al.
Status: final response (author comments only)
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RC1: 'Comment on hess-2023-140', Anonymous Referee #1, 27 Jun 2023
The present paper proposes a novel framework for tracking drought cascades across 10 multiple systems by utilizing dynamic space-time motion similarities. The method seems innovative and the topic interesting. However, due to problems in logic, I would recommend major revision before moving to the next step. The comments are as follows:
Major comments
- The introduction of the method, which is the core of the study, is unclear. For example, are the drought pixels a function of (lat,lon) or (time, lat,lon). How are the drought cells clustered, using which criteria or method. What metric(s) is used to determine similarity? I see some in the paragraph but the vague description using the text is insufficient in clarification.
- Loose logic problem. For example, in the method part (section 2.3), the introduction in section 2.3 seems too vague, and does not give you a general idea of the method. It does not give you an idea of the inner-connections between the sub-sections. Also, the section 2.3 has too much sub-sections that is un-necessary, consider combining the sub-sections to make the section more neatly.
- Confusing subsection in discussion. There’s no need to break into too many subsections. Also, it is not clearly to me what the discussions are for? In common discussions, it is usually to raise up an interesting issue with one or more paragraphs. But the discussion here seems to be more apt in the results. Other paragraphs about the issue can be put in discussion.
- Is there a comparison with the other drought identification methods/indices? It would be good if the authors are comparing this method to other similar methods or single indices to strengthen the core value of this method.
Minor comments
- Line 36, “arising from” -> “arise from”.
- Line 53, “compared to defining the drought…” It is redundant.
- Line 72 “Based on above….” It seems weird to say “based on above” in here. The authors seem to have point out the situation in characterizing drought. The logic then is to “fill the gap” rather than to sum up. So it may be better to use “To fill gap..” or similar expression.
- Line 76, “Central Asia (CA) is a typical arid and semi-arid region…..”. The sudden jump from discussion of method to introduction of Central Asia in the last paragraph seems weird. It may be better just to say something like “test this method in Central Asia which is a typical arid/semi-arid region”. It is better to put more info in the section 2.1 study area.
- Line 82, “The findings of this study are anticipated to …….” The whole sentence may be better in the conclusion section rather than introduction.
- Line 83, Please add a section introduction of the sections in the last of the paragraph.
- Line 84 “Material & Methods”-> “Data and method”.
Citation: https://doi.org/10.5194/hess-2023-140-RC1 -
AC1: 'Reply on RC1', Lu Tian, 07 Sep 2023
Dear Editor and Reviewer,
Thank you for your letter and the reviewer’s comments concerning our manuscript entitled "Drought cascades across multiple systems in Central Asia identified based on the dynamic space-time motion approach" (hess-2023-140). These comments are valuable and helpful for revising and improving our paper and providing significance to our research. We have carefully considered the words and made corresponding responses. The responses to the reviewer's comments are listed below.Best regards
Lu Tian, on behalf of all authors
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RC2: 'Comment on hess-2023-140', Anonymous Referee #2, 07 Jul 2023
This study presents a new framework to characterize and track drought events across multiple systems using the spatiotemporal evolution of deficits in precipitation followed by deficits in evapotranspiration, run-off and root-zone soil moisture.
I think this is an important study which will help to better understand the drought occurrence, its evolution and its associated impact on the ecosystem. I do however have some concerns/confusions that I would like to see clarified:
1: The study identifies 503 drought cascading events with multiple combinations within 2-system, 3-system and 4-system droughts. However, there is little discussion about the expected mechanism behind the occurrence of these drought cascading events mentioned in Table 1 and Figure 3.
2: Given the strong coupling between soil-moisture and evaporation (under water-limited regime), why would we expect the two droughts to occur over different periods? The decrease in actual evaporation should be associated with an enhanced water stress so should not we expect the soil-moisture to reduce at the same time?
3: The study uses evaporative deficit as difference between actual and potential evaporation from GLEAM and the soil-moisture stress from GLDASv2.0-Noah model. How well the GLDAS and GLEAM dataset represent the soil moisture-evaporation coupling?
4: The climatology of Central Asia is described in Figure 1 and section 2.1. But did authors also find any pattern between climatology/landcover-type and different kind of cascading events?
5: The study used PCP drought as a commencement for the event. Can the antecedent hydrologic conditions before the PCP event also govern the evolution? For instance, over a wet condition, I would expect Precipitation deficit (PCP) to be followed by energy limited evaporation with increased evaporative demand and that should lead to run-off deficit and eventually drying up the soil so an evaporation deficit i.e., PCP + Runoff + ET. Conversely over a dry surface, ET droughts may be triggered faster due to vegetation-water stress. Also, the precipitation deficits over dry regions could be lower so they may not directly translate into runoff droughts.
6: High intensity PCP droughts leads to increase in number of cascading system (Figure 8b). Can the intensity of PCP drought may also affect the type of cascading evolution?
7: Does the presence of vegetation type over a region affect the pattern of drought cascades? For instance, over region where plants have deep-roots, they may still evaporate during dry periods and may only result in PCP + Runoff type droughts
Minor Comment/Technical corrections:
Line 435: “last” instead of “latest”?
Given that Violin plots are not very common, it may be helpful for the readers if authors could briefly describe the statistics of the plot before introducing them.
Citation: https://doi.org/10.5194/hess-2023-140-RC2 -
AC2: 'Reply on RC2', Lu Tian, 07 Sep 2023
Dear Editor and Reviewer,
Thank you for your letter and the reviewer’s comments concerning our manuscript entitled "Drought cascades across multiple systems in Central Asia identified based on the dynamic space-time motion approach" (hess-2023-140). The comments involve the driven mechanism of cascading drought, which is valuable and helpful for revising and improving our paper and providing significance to our research. We have taken care of the words carefully and made corresponding responses. The responses to the reviewer's comments are listed below.Best regards,
Lu Tian, on behalf all authors
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AC2: 'Reply on RC2', Lu Tian, 07 Sep 2023
Lu Tian et al.
Lu Tian et al.
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