the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 20 Feb 2024
Review article: Drought as a continuum: memory effects in interlinked hydrological, ecological, and social systems
Abstract. Droughts are often long lasting phenomena, without a distinct start or end, and with impacts cascading across sectors and systems, creating long-term legacies. Nevertheless, our current perception and management of droughts and their impacts is often event-based, which can limit the effective assessment of drought risks and reduction of drought impacts. Here, we advocate for changing this perspective and viewing drought as a hydro-eco-social continuum. We take a systems theory perspective and focus on how “memory” causes feedback and interactions between parts of the interconnected systems at different time scales. We first discuss the characteristics of the drought continuum with a focus on the hydrological, ecological, and social systems separately; and then study the system of systems. Our analysis is based on a review of the literature and a study of five cases: Chile, the Colorado River Basin in the US, Northeast Brazil, Kenya, and the Rhine River Basin in Northwest Europe. We find that the memories of past dry and wet periods, carried by both bio-physical (e.g. groundwater, vegetation) and social systems (e.g. people, governance), influence how future drought risk manifests. We identify four archetypes of drought dynamics: Impact & recovery; Slow resilience-building; Gradual collapse; and High resilience, big shock. The interactions between the hydrological, ecological and social systems result in systems shifting between these types, which plays out differently in the five case studies. We call for more research on drought pre-conditions and recovery in different systems, on dynamics cascading between systems and triggering system changes, and on dynamic vulnerability and maladaptation. Additionally, we argue for more continuous monitoring of drought hazards and impacts, modelling tools that better incorporate memories and adaptation responses, and management strategies that increase social and institutional memory to better deal with the complex hydro-eco-social drought continuum and identify effective pathways to adaptation.
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CC1: 'Comment on egusphere-2024-421', carolina ojeda leal, 22 Feb 2024
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In this article, more than 40 well-recognized authors proposed a new shift in the studies of drought phenomena. They took 5 cases from different parts of the world and applied an adapted version of system theories (resilience, SES, human-nature coupled systems, and collapse) to argue that drought is a long-term phenomenon that damages multiple systems (hydrological, ecological, and social). Overall, it is a very well-written article, with abundant literature references and the scientific rigor expected in a literature review made by 42 people. Nevertheless, it is so extensive and theoretically dense that sometimes looks more like a book chapter or white paper rather than a scientific article of NHESS, which in my impression intended to be more applied.
I have a few comments to improve the article:
1. In the section "4.3.2 Systems Influencing Each Other" paragraph 590 I suggest changing the term "industrial tree plantations" to "exotic species monocultures (e.g., pine, eucalyptus)". Also, I suggest citing CONAF in those statistics of data about wildfires resulting from their excellent work. Moreover, I do not understand from that paragraph if the “megadrought” in Chile and the social system (anthropical fire ignition + exotic species monocultures) by themselves instigated changes in the hydrological system which was translated into the extension of fire season. It was confusing to read sometimes because created the illusion that both local drivers (“megadrought” + social system) without global climate change could alter the Chilean fire seasonality, but it could be because the only data available to analyze the wildfire damage is from CONAF which started to keep it from 1985 until today. To establish more clearly that hypothesis it could be necessary to expand the four-decade analysis to incorporate the memory of pre “megadrought” time with appropriate literature if is relevant to the topic.
2. In paragraph 700 I don't understand the phrase: "More research is needed on interactions and feedback between systems related to drought impacts and responses. For example, studies on the interactions between drought and wildfires should not only include ecological processes but also hydro-climatic and social processes". In my opinion, many studies have observed those cascading phenomena already as a prolonged drought changes social dynamics associated with crops, forestry, rural traditions, etc., and water scarcity makes them established long-term wildfire drivers. So, what more studies need to be made related to wildfires and drought? I suggest deleting it or reinforcing it if is relevant to the topic of interactions and feedback between systems.
2. The appendix section provides abundant information about the cases but it is not homogeneous in the case selection (e.g. Chile presents few basins in the center, and the US presents one basin which is the Colorado River Basin (United States), The Horn of Africa (HOA) which is an entire region, etc.) and how they were extensively written. Also, I miss a global map in the beginning to locate the 5 cases. What happened with the ecosystem part of APPENDIX 3 - Case study Northeast Brazil? It is blank.
Citation: https://doi.org/10.5194/egusphere-2024-421-CC1 -
AC1: 'Comment on egusphere-2024-421', Anne Van Loon, 22 Feb 2024
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Due to an oversight, we have submitted the manuscript file with an old version of the appendix (Appendix 1 - Chile case study). Attached to this comment, we now uploaded the correct final version of Appendix 1 - Case study Chile. We would like to ask reviewers and other colleagues to refer to this version of Appendix 1 for review.
Thanks, Anne Van Loon (on behalf of all co-authors)
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RC1: 'Comment on egusphere-2024-421', Rene Orth, 21 Mar 2024
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Review of van Loon et al., manuscript number egusphere-2024-421
“Review article: Drought as a continuum: memory effects in interlinked hydrological, ecological, and social systems”This review paper summarises the state of the art of the research on drought impacts on hydrology, ecology and society. The authors advocate for viewing droughts as multi-spheres phenomena, and to move away from event-based drought analyses. They conduct five case studies of drought impacts in different regions of the world to illustrate specific drivers and implications, and use this to showcase a separation of droughts into four archetypes with distinct temporal dynamics.
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Recommendation:
I think the paper requires moderate revisions.The topic of this review is interesting and timely, and it is a great fit for the readership of NHESS.
It serves as a useful summary of the state of the art of drought impacts across individual spheres, and at the same time it adds a new perspective by focusing on the complex nature and implications of droughts across geo- and socio-spheres. I like that this review is motivating more comprehensive research on droughts, which takes into account multiple spheres and can provide more profound insights. This can help to steer the very active research in this field. Consequently, research can then probably also yield more effective and sustainable management options. Benefits of this interdisciplinary research approach are convincingly illustrated with the case studies that include detailed descriptions and comparisons of common drought response strategies.However, before the paper is ready for publication I would recommend to address a few discussion points:
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General comments:
(1)
I like the consideration of the concept of drought memory across time and spheres. But currently the term memory is used in a somewhat confusing way as it is (i) used with and without “” (“memory” and memory) while the difference is not clear, and (ii) only defined in line 165 after it has been used several times. Another point in this context is that the paper focuses on development and implications of memory, but not so much on its dissipation through e.g. meteorological variability which can shorten memory more or less strong.(2)
The outlook and recommendations section provides useful advice to the community. One aspect that I am still missing is some discussion or even guidance on how we could promote more interdisciplinary research approaching drought as a hydro-eco-social continuum. Given the focus and arguments of this paper, this could be another important contribution it could make. I can think of two directions in this context:
— Observational data: This is critically needed for enhancing process understanding and for constraining more sophisticated models. Following the systems approach of the paper, also data needs will change. For example social system impacts and characteristics need to be quantified in addition to (more readily available?) data on hydrological and ecological systems, and using such data streams from different spheres together might pose challenges with respect to spatial and temporal resolution and coverage of the data. It would be great if the authors could add some thoughts or even recommendations in this direction.
— Spatial and temporal scales: An issue which becomes apparent from the comparison of hydrological, ecological and social aspects of drought research are the different spatial and temporal scales considered within, but even more across these spheres. This raises the question how to determine adequate scales, and to which extent we can or should ensure to aim for comparable scales in order to facilitate interdisciplinary drought research across spheres. See for example De Polt et al. 2023.(3)
Related to the drought trajectory types, in my understanding type 4 is similar to type 1b such that I do not see the necessity for a fourth category. Also, I feel that the addition of “big shock” in the name of type 4 is not needed as this may not necessarily be the case, which can also be seen from the case study examples.I do not wish to remain anonymous - Rene Orth.
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Specific comments:
lines 53, 73, and others: Maybe some discussion can be added on the reasons for adopting an event-based perspective on droughts in past and present research. I think for example that some form of quantification of drought time periods (even though they may be different across spheres) is necessary for separating droughts from hydrological variability.
line 90: Here you could also cite O & Park 2024
line 139: “interacting systems interacting” is a bit too interactive I think
lines 148-157: I like the mention to the concept of socio-ecological systems and Earth system science. However, it could be more integrated and compared with the drought continuum concept proposed here.
line 285: Here you could also cite Li et al. 2023
line 294: would remove “depleting” here such that the previous “reducing” applies for the decomposition argument
line 392: add “on rivers” after “reductions in goods transported”
lines 375, 393, and others: it is interesting to see the similarities in the drought response of social system to that of ecological systems
line 718: should be section 5.2
Table 1, bottom right box: Maybe replace “prevent” with “hinder”
References:
De Polt, K., et al., Quantifying impact-relevant heatwave durations, Env. Res. Lett. 18, 104005 (2023).
Li, W., et al., Widespread and complex drought effects on vegetation physiology inferred from space, Nat. Comms., 14, 4640 (2023).
O, S. and S.K. Park, Global ecosystem responses to flash droughts are modulated by background climate and vegetation conditions, Communications Earth & Environment, 5, 88 (2024).Citation: https://doi.org/10.5194/egusphere-2024-421-RC1 -
RC2: 'Comment on egusphere-2024-421', Ana Iglesias, 08 Apr 2024
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The review article is interesting and well written, supporting the well-established call for a systems perspective to successfully manage all natural and man-made hazards, including adaptation to climate change. The article is a very major effort from the earth sciences community to engage with social sciences, and in this sense, its value is great. Section 3 of the manuscript is extremely well written and provides very interesting information.
However, the current version of the paper does not completely respond to the anticipated goal. Some changes may be interesting to further engage all readers, to provide an accurate state of the art, and to make progress to decrease the social damage by drought.
Some minor comments:
- Recognise the immense systemic contribution made in the developing of drought management plans.
- Further develop and discuss the idea of “memories” that is a well-known determinant to human responses to all adverse events. This could be included in the drought preconditions and recovery in different systems.
- The idea of dynamic vulnerability and maladaptation is extremely interesting, but not completely developed in the paper.
- In my view, trendy terms such as “flash droughts” of “mega-droughts” do not add and substantial concept and detract from the logic of the paper. But I do not object to their use if the authors really like them.
- Eliminate the statements such as “we argue that understanding drought requires taking into account not only physical (hydro-meteorological) processes, but also ecological (environmental) and social (economical, political) processes to assess drought risks” that are not original. These very well-established ideas need to change “we argue” to “we support”. (this is only one example; more similar statements are throughout the text).
- Section 2 is the weakest section and needs to be re-written completely. Table 1 is extremely limited.
- Section 3 is the strongest section, especially Section 3.1. Minor changes in Sections 3.2 and 3.3 would bring them to the excellent level of Section 3.1.
- Section 4 could be more explicit the application of the framework to the case studies.
- Section 5 seems to be judgemental and with limited applications for drought management practitioners. A shorter section, more related to the on-going policy development could be more useful.
- Finally, as many papers written mainly by non-social scientists, the link to social sciences seems to be the inclusion of extraordinary social scientist in the reference list. Here is the case of E. Ostrom. In my view, dropping names is rarely successful. If the authors want to recognise concrete contributions or linkages to their work, they should be more concrete.
Citation: https://doi.org/10.5194/egusphere-2024-421-RC2
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