The agricultural expansion in South America&rsquo;s Dry Chaco: Regional hydroclimate effects

Bracalenti, María Agostina; Müller, Omar Vicente; Lovino, Miguel Angel; Berbery, Ernesto Hugo

doi:https://doi.org/10.5194/egusphere-2023-1427

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https://doi.org/10.5194/egusphere-2023-1427

Preprints

11 Jul 2023

| 11 Jul 2023

The agricultural expansion in South America’s Dry Chaco: Regional hydroclimate effects

María Agostina Bracalenti, Omar Vicente Müller, Miguel Angel Lovino, and Ernesto Hugo Berbery

Abstract. The Gran Chaco ecoregion is South America’s largest remaining continuous stretch of dry forest. It has experienced intensive deforestation, mainly in the western part known as Dry Chaco, resulting in the highest rate of dry forest loss globally between 2000 and 2012. The replacement of natural vegetation with other land uses modifies the surface’s biophysical properties, affecting heat and water fluxes and modifying the regional climate. This study examines land use and land cover changes (LULCCs) in Dry Chaco from 2001 to 2015, their effects on local and non-local climate, and explores the potential impacts of future agricultural expansion in the region. To this end, Weather Research and Forecasting (WRF) model simulations are performed for two scenarios: the first one evaluates the observed land cover changes between 2001 and 2015 that covered 8 % of the total area of Dry Chaco; the second scenario assumes an intensive agricultural expansion within the Dry Chaco. In both scenarios, deforestation processes lead to decreases in LAI, increases in albedo, and reductions in stomatal resistance, reducing the net surface radiation and, correspondingly, a decrease in turbulent fluxes suggesting a decline in available energy in the boundary layer. The result is an overall weakening of the water cycle in the Dry Chaco and, most prominently, implies a reduction in precipitation. A feedback loop develops since dry soil absorbs significantly less solar radiation than moist soil. Finally, the simulations suggest that the Dry Chaco would intensify its aridity, extending the drier and hotter conditions into the Humid Chaco.

Received: 28 Jun 2023 – Discussion started: 11 Jul 2023

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Journal article(s) based on this preprint

25 Jul 2024

The agricultural expansion in South America's Dry Chaco: regional hydroclimate effects

María Agostina Bracalenti, Omar V. Müller, Miguel A. Lovino, and Ernesto Hugo Berbery

Hydrol. Earth Syst. Sci., 28, 3281–3303, https://doi.org/10.5194/hess-28-3281-2024,https://doi.org/10.5194/hess-28-3281-2024, 2024

Short summary

María Agostina Bracalenti, Omar Vicente Müller, Miguel Angel Lovino, and Ernesto Hugo Berbery

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-1427', Anonymous Referee #1, 26 Sep 2023

This paper investigates the impact of the intensive deforestation in favor of agricultural expansion on the hydro-climatic regime of the South America’s Dry Chaco region. The paper addresses some important questions about the feedback of LULCC on the vegetation growth (LAI, albedo, stomatal resistance) and the hydro-climatic response response (precipitation, soil moisture and runoff). This study uses WRF modelling to simulate hydro-climatic responses to deforestation scenarios. Analysing the impacts of deforestation in the Dry Chaco on local hydrology and climate, as well as in the neighbouring (which has been little affected by deforestation), is also interesting for understanding the effects at different spatial scales.
I however have a number of comments that need to be addressed – please see below.
Main comments:
1) The simulations are carried out over a 2-year period (2014-2016 for the reference simulation) which seems very short to analyze the effects of deforestation on the hydro-climatic response.
If possible, I would recommend to validate WRF on the 2014-2016 period (to validate over a period with few changes in land use), and then to simulate the control and scenario simulations over a longer period (30 years or at least >10 years) so that the results are not affected by the inter-annual climate variability.
The authors should at least specify whether the 2014-2016 simulation period corresponds to an El Nino or La Nina episode in order to know under which pattern of atmospheric circulation the simulations are being carried out.
2) This paper studies the effects of LULCC by analyzing the changes in various simulated variables (energy budget, precipitation, evapotranspiration, soil moisture, runoff, LAI, albedo, stomatal resistance) to different landuse conditions.
However, the model is only evaluated using observed temperature, precipitation and soil moisture datasets. It is therefore difficult to draw any conclusions about the effects of deforestation on the other unvalidated variables.
In my opinion the modelling experiment is not robust enough to draw general conclusions about the physical processes impacted by deforestation in the Dry Chaco. However, the modelling experiment remains interesting and the authors could instead present their results as a sensitivity analysis of WRF simulations to different initial landuse conditions.
3) The uncertainties related to the model and its internal variability should to be discussed. How can model parameterisation and initial conditions impact on the simulated results?
Regarding the uncertainty related to initial conditions, the authors mention in the presentation of the experimental design that each scenario was conducted with an ensemble of 4 members with identical parameterisations but different initial conditions that are 24-hr apart. But the simulations obtained with the 4 members do not appear in the results (only the average). It would be interesting to analyze and show some results about the sensitivity of the simulated variables (e.g. precipitation, soil moisture, runoff) to the different initial conditions.
Regarding the uncertainty related to the model parameterisation, it would be interesting to include simulations to test the sensitivity to few selected model options or parameter, or at least discuss the results referring to studies from the literature that conducted a full internal variability analysis of the WRF model.
4) The paper would benefit from a more detailed literature review and a proper discussion section to discuss the above points. The results of the first part concerning the observed changes in the Dry Chaco between 2001 and 2015 and future trends of deforestation should also be discussed and compared with other studies from the literature.
Detailed comments: Please see Supplement file.

Citation: https://doi.org/10.5194/egusphere-2023-1427-RC1
- AC1: 'Reply on RC1', Omar Müller, 13 Dec 2023
  
  I express our gratitude to the Reviewer on behalf of all co-authors for investing valuable time in the thorough review of our manuscript. A comprehensive response to each specific comment is provided in the attached file.
  
  Citation: https://doi.org/10.5194/egusphere-2023-1427-AC1
RC2:
'Comment on egusphere-2023-1427', Anonymous Referee #2, 15 Nov 2023

This manuscript conducts a set of WRF-Noah simulations to examine the impacts of historical land use and land cover change (LULCC) and potential agriculture expansion in the future. By comparing historical, control, and future cases, this work illustrates the drying climatology and land conditions (e.g., warming surface temperature and decreased precipitation and soil moisture). However, several problems and limitations exist; thus, a major point-to-point revision is needed. For example, at least several months of spin-up are needed to initialize the soil moisture and allow the surface fluxes to respond to LULCCs; however, the manuscript doesn’t mention if the authors spin up the WRF-Noah before the formal runs. Also, the authors haven’t confirmed if WRF-Noah can simulate the specific mechanisms discussed. For example, the authors should confirm if WRF-Noah can resolve the remote effects of LULCC. Detailed comments can be found attached.

Citation: https://doi.org/10.5194/egusphere-2023-1427-RC2
- AC2: 'Reply on RC2', Omar Müller, 13 Dec 2023
  
  On behalf of all co-authors, we sincerely appreciate the constructive feedback provided by Referee #2. Please find our detailed responses to each comment in the attached file.
  
  Citation: https://doi.org/10.5194/egusphere-2023-1427-AC2

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-1427', Anonymous Referee #1, 26 Sep 2023

This paper investigates the impact of the intensive deforestation in favor of agricultural expansion on the hydro-climatic regime of the South America’s Dry Chaco region. The paper addresses some important questions about the feedback of LULCC on the vegetation growth (LAI, albedo, stomatal resistance) and the hydro-climatic response response (precipitation, soil moisture and runoff). This study uses WRF modelling to simulate hydro-climatic responses to deforestation scenarios. Analysing the impacts of deforestation in the Dry Chaco on local hydrology and climate, as well as in the neighbouring (which has been little affected by deforestation), is also interesting for understanding the effects at different spatial scales.
I however have a number of comments that need to be addressed – please see below.
Main comments:
1) The simulations are carried out over a 2-year period (2014-2016 for the reference simulation) which seems very short to analyze the effects of deforestation on the hydro-climatic response.
If possible, I would recommend to validate WRF on the 2014-2016 period (to validate over a period with few changes in land use), and then to simulate the control and scenario simulations over a longer period (30 years or at least >10 years) so that the results are not affected by the inter-annual climate variability.
The authors should at least specify whether the 2014-2016 simulation period corresponds to an El Nino or La Nina episode in order to know under which pattern of atmospheric circulation the simulations are being carried out.
2) This paper studies the effects of LULCC by analyzing the changes in various simulated variables (energy budget, precipitation, evapotranspiration, soil moisture, runoff, LAI, albedo, stomatal resistance) to different landuse conditions.
However, the model is only evaluated using observed temperature, precipitation and soil moisture datasets. It is therefore difficult to draw any conclusions about the effects of deforestation on the other unvalidated variables.
In my opinion the modelling experiment is not robust enough to draw general conclusions about the physical processes impacted by deforestation in the Dry Chaco. However, the modelling experiment remains interesting and the authors could instead present their results as a sensitivity analysis of WRF simulations to different initial landuse conditions.
3) The uncertainties related to the model and its internal variability should to be discussed. How can model parameterisation and initial conditions impact on the simulated results?
Regarding the uncertainty related to initial conditions, the authors mention in the presentation of the experimental design that each scenario was conducted with an ensemble of 4 members with identical parameterisations but different initial conditions that are 24-hr apart. But the simulations obtained with the 4 members do not appear in the results (only the average). It would be interesting to analyze and show some results about the sensitivity of the simulated variables (e.g. precipitation, soil moisture, runoff) to the different initial conditions.
Regarding the uncertainty related to the model parameterisation, it would be interesting to include simulations to test the sensitivity to few selected model options or parameter, or at least discuss the results referring to studies from the literature that conducted a full internal variability analysis of the WRF model.
4) The paper would benefit from a more detailed literature review and a proper discussion section to discuss the above points. The results of the first part concerning the observed changes in the Dry Chaco between 2001 and 2015 and future trends of deforestation should also be discussed and compared with other studies from the literature.
Detailed comments: Please see Supplement file.

Citation: https://doi.org/10.5194/egusphere-2023-1427-RC1
- AC1: 'Reply on RC1', Omar Müller, 13 Dec 2023
  
  I express our gratitude to the Reviewer on behalf of all co-authors for investing valuable time in the thorough review of our manuscript. A comprehensive response to each specific comment is provided in the attached file.
  
  Citation: https://doi.org/10.5194/egusphere-2023-1427-AC1
RC2:
'Comment on egusphere-2023-1427', Anonymous Referee #2, 15 Nov 2023

This manuscript conducts a set of WRF-Noah simulations to examine the impacts of historical land use and land cover change (LULCC) and potential agriculture expansion in the future. By comparing historical, control, and future cases, this work illustrates the drying climatology and land conditions (e.g., warming surface temperature and decreased precipitation and soil moisture). However, several problems and limitations exist; thus, a major point-to-point revision is needed. For example, at least several months of spin-up are needed to initialize the soil moisture and allow the surface fluxes to respond to LULCCs; however, the manuscript doesn’t mention if the authors spin up the WRF-Noah before the formal runs. Also, the authors haven’t confirmed if WRF-Noah can simulate the specific mechanisms discussed. For example, the authors should confirm if WRF-Noah can resolve the remote effects of LULCC. Detailed comments can be found attached.

Citation: https://doi.org/10.5194/egusphere-2023-1427-RC2
- AC2: 'Reply on RC2', Omar Müller, 13 Dec 2023
  
  On behalf of all co-authors, we sincerely appreciate the constructive feedback provided by Referee #2. Please find our detailed responses to each comment in the attached file.
  
  Citation: https://doi.org/10.5194/egusphere-2023-1427-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

ED: Publish subject to revisions (further review by editor and referees) (08 Jan 2024) by Yongping Wei

AR by Omar Müller on behalf of the Authors (19 Feb 2024) Author's response Author's tracked changes Manuscript

ED: Publish subject to revisions (further review by editor and referees) (27 Feb 2024) by Yongping Wei

ED: Referee Nomination & Report Request started (20 Mar 2024) by Yongping Wei

RR by Anonymous Referee #2 (22 Apr 2024)

RR by Anonymous Referee #1 (26 Apr 2024)

Suggestions for revision or reasons for rejection

In this revised manuscript, the authors have responded to all the comments made by the 2 reviewers. The changes made have improved the quality of the manuscript, in particular through:
- the addition of references in the introduction, providing a more complete and up-to-date bibliographic review
- the addition of information regarding the climatic context of the Chaco region
- the addition of information regarding the physical processes represented in WRF-Noah
- the addition of results and discussion on the uncertainty linked to the internal variability of the model
- the re-structuring of the paper with a section dedicated to the evaluation of the model and a discussion section

However, I do not always agree with the answers and modifications made by the authors concerning the 2 points discussed below. These 2 points do not undermine the method or the results of this study, but in my opinion some parts of the discussion section needs to rewritten and the results need to be more nuanced.

1) Both reviewers pointed out that the duration of the simulations (2.5 years) was too short to draw conclusions regarding the hydro-climatic impacts of LULCC, given that hydro-climatic regimes are generally assessed over periods of around 30 years.
The authors rightly pointed out that the calculation times are too long to extend the simulation period considerably.
However, I do not agree with the sentence L432-435 (see below) which, in my opinion, minimizes this limit. The authors could also go further in the discussion section by giving some perspective for assessing the impact of climate variability on the simulation results (perhaps like repeating the experiment over another 3 years period with contrasted climatic conditions for initialization and boundary conditions).
The conclusion should also be more nuanced, pointing out that simulations lasting 2.5 years are too short to assess the impact on the hydro-climatic regime, and that further studies will have to be carried out to confirm these results.

L432-435 « While longer simulations could offer understanding under diverse large-scale atmospheric conditions, the length of these high-resolution simulations (determined by the computational capacity) provides valuable insights for assessing the land-atmosphere processes, which occur on daily to monthly time scales. »

2) Regarding the evaluation of the model on a broader set of variables, I do not agree with the sentence L442-445 (see below), as (i) I do not see why satellite products for variables such as LAI or albedo could not be used for model evaluation as they do not really differ from the SMOPS and HSAF products used to evaluate soil moisture in this study, and (ii) models inter-comparisons for the variables that cannot be directly measured could still provide some useful information about the modelling uncertainty of these variables.

The authors should point out in the discussion section that the impacts of LULCC are analyzed on simulated variables that have not all been validated (LAI, albedo, radiation, heat fluxes and runoff) which limits the ability to draw conclusions about the chain of processes affected.
Although it was not possible to evaluate the model on a larger set of variables in this study, the authors could mention in the discussion that this will be an important issue to address in future studies in order to assess the uncertainty of the modelling on these variables and increase confidence in the results obtained.

L442-445 « Other variables (radiation, heat fluxes, runoff, etc) could be included in the evaluation. However, their derivation involves algorithms or models with inherent approximations and uncertainties, which cannot be verified by in-situ measurements given the lack of field observations of non-conventional variables in the Gran Chaco region. Thus, the validation of such variables would be reduced to a comparison between tow disparate estimates without the inclusion of ground truth. »

Technical remarks:

L74 Rephrasing suggestion to avoid the use of « more realistic scenarios » which is a bit confusing :
« In this way, this study considers both observed and possible future expansions of LULCCs, offering a nuanced understanding of the actual and potential impacts on regional climate. By considering these two scenarios of LULCCs, it is possible to hypothesize how agricultural expansion in one region influences the hydroclimate of another, which is crucial for effective regional land use planning on a topic prone to developing socio-ecological conflicts associated with LULCCs. »

L269-270 Please name the months instead of seasons to avoid confusions (e.g. JJA instead of winter)

L445 « two » instead of « tow »

L511 Rephrasing suggestion :
« The simulations indicate an average reduction of net surface radiation and surface energy fluxes, which in turn, lead to drier hydrological conditions overall in terms of precipitation and runoff. »

L519 Replace « may have not be » with « may not be »

L525 Remove WFDEI dataset from the list and add url to ERA5 dataset

L636 Please move the Flanagan et al. 2021 reference higher in the list to maintain alphabetical order.

L759 Replace WFDEI with ERA5

Figure 7 : Does Fig7a show the mean between CRU and ERA5 ?
Table in Fig7d replace « promedio » with « mean »

Figure 10 : Boxplot values for runoff (10d) seem incoherent with text L350 « The reduced precipitation and drier soils end up affecting the total runoff, which presents a net reduction in the Dry Chaco of -2.1 % in local areas and -5.5% in non-local areas (Fig. 10d). ». Please check the consistency between Fig10d and L350.

Figure 13 : Same remark as Figure 10. Please check consistency between Fig13d and L386 « runoff is reduced by -5 % on average ».

Hide

ED: Publish subject to minor revisions (review by editor) (19 May 2024) by Yongping Wei

AR by Omar Müller on behalf of the Authors (27 May 2024) Author's response Author's tracked changes Manuscript

ED: Publish as is (05 Jun 2024) by Yongping Wei

AR by Omar Müller on behalf of the Authors (10 Jun 2024)

Journal article(s) based on this preprint

25 Jul 2024

The agricultural expansion in South America's Dry Chaco: regional hydroclimate effects

María Agostina Bracalenti, Omar V. Müller, Miguel A. Lovino, and Ernesto Hugo Berbery

Hydrol. Earth Syst. Sci., 28, 3281–3303, https://doi.org/10.5194/hess-28-3281-2024,https://doi.org/10.5194/hess-28-3281-2024, 2024

Short summary

María Agostina Bracalenti, Omar Vicente Müller, Miguel Angel Lovino, and Ernesto Hugo Berbery

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Short summary

The Gran Chaco is a large dry forest in South America that has been heavily deforested, particularly in the Dry Chaco subregion. This deforestation has changed the land’s characteristics, affecting the local and regional climate. The study reveals that deforestation has resulted in reduced precipitation, soil moisture, and runoff, and if intensive agriculture continues, it could make summers in this arid region even drier and hotter.


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