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Impacts of land-surface heterogeneities and Amazonian deforestation on the wet season onset in southern Amazon

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Abstract

Continued Amazonian deforestation perturbs the surface turbulent fluxes which are important for building the conditions for the wet season onset in the southern Amazon. This work evaluates the impacts of tropical deforestation on the onset and development of the Amazonian rainy season using a weather typing approach. We use 19-year simulations (2001–2019) with the Regional Earth System Model from the Institute Pierre Simone Laplace (RegIPSL) with twin control/deforestation experiments. RegIPSL represents the dominant modes or the atmospheric circulation patterns (CPs) of the daily-to-decadal circulation variability in tropical South America, and the evolution of atmospheric and surface conditions along the dry-to-wet transition period. According to RegIPSL, forests and crops contribute differently to the onset. During the dry-to-wet transition period, croplands/grasslands present a stronger shallow convection driven by a higher atmospheric temperature. Large-scale subsidence suppresses low-level convection in the region and deep convection only persists over forests where the atmosphere presents more convective potential energy. After the onset and the establishment of large-scale rainfall structures, both land covers behave similarly in terms of surface fluxes. Deforestation decreases the frequency of the CP typically linked to the onset. Changes in the spatial structure and frequency of the wet season CPs reinforce the hypothesis of a deforestation-induced dry season lengthening. Variations in the CP frequency and characteristic rainfall have opposite effects on accumulated rainfall during the dry-to-wet transition period. Whereas alterations in frequency are associated with a regional circulation response, changes in the CP characteristic rainfall correspond to a local response to deforestation.

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All dataset sources, except RegIPSL modeling results, have been properly referenced by showing the source (web site links). The datasets generated during the current study (RegIPSL outputs) are available from the corresponding author on reasonable request.

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Acknowledgements

This research has been supported by the French AMANECER-MOPGA project funded by ANR and IRD (ANR-18-MPGA-0008), and by the ACE-Amazon project funded by the regional program CLIMAT-AmSud (21-CLIMAT-01). MINCyT-ECOS Sud ref. A18D04 (Argentina-France) and INSU LEFE ref. 12962 are also acknowledged. At the same time, this work was granted access to the HPC resources of IDRIS under the allocation 2021-101054 made by GENCI. Simulations were run on the Jean Zay HPC at the French computing center IDRIS. The authors would also like to thank the following agencies/organizations for providing access to data: The Climate Hazards Group Infrared Precipitation for providing CHIRPS, Paca, V. H. d. M. (2019) for providing ET-Amazon and the Copernicus Climate Change Service (C3S) for providing horizontal wind fields and surface fluxes from ERA5 and ERA5-Land. Anthony Schrapffer was funded by PICT 2014-0887, PICT-2015-3097, PICT-2017-1406 (ANPCyT, Argentina). Paola A. Arias was funded by MINCIENCIAS through the grant No. 80740-490-2020.

Funding

This research has been supported by the French AMANECER-MOPGA project funded by ANR and IRD (ANR-18-MPGA-0008), and by the ACE-Amazon project funded by the regional program CLIMAT-AmSud (21-CLIMAT-01). At the same time, this work was granted access to the HPC resources of IDRIS under the allocation 2021-101054 made by GENCI. Anthony Schrapffer was funded by PICT 2014-0887, PICT-2015-3097, PICT-2017-1406 (ANPCyT, Argentina). Paola A. Arias was funded by MINCIENCIAS through the grant No. 80740-490-2020.

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All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by JPS. The first draft of the manuscript was written by JPS and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

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Correspondence to Juan Pablo Sierra.

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382_2023_6835_MOESM1_ESM.eps

Fig. S1 Mean annual cycle in LBA stations Fazenda Nossa Senhora de Aparecida (FNS, deforested area) and Rondonia Jaru Biological Reserve Aparecida (RJA, forested area) in black lines, and RegIPSL-Control in cyan lines, for: rainfall over a cropland/grassland and b forest in mm day-1; evapotranspiration over c cropland/grassland and d forest in mm day-1; incoming shortwave radiation over e cropland/grassland and f forest in W m-2; outgoing shortwave radiation over g cropland/grassland and h forest in W m-2; incoming longwave radiation over i cropland/grassland and j forest in W m-2; outgoing longwave radiation over k cropland/grassland and l forest in W m-2; net surface radiation over m cropland/grassland and n forest in W m-2. The period 2001-2002 is used for both model and observations. RegIPSL-Control values are computed as the spatial mean of surface variables over an area of 100 km x 100 km surrounding the two stations but masking over forest and non-forest. (EPS 398 KB)

382_2023_6835_MOESM2_ESM.eps

Fig. S2 Rainfall and 850 hPa horizontal wind anomalies composites (vs the annual mean) for the 9 circulation patterns (CPs) defined from the k-means clustering analysis using ERA5 for winds and CHIRPS for rainfall. Rainfall (shaded) is in percentage respect to the inter-annual mean and horizontal winds at 850 hPa (vectors) are adimensional. (EPS 10840 KB)

382_2023_6835_MOESM3_ESM.eps

Fig. S3 Taylor diagrams of the spatial patterns of: a rainfall anomalies b zonal component anomalies at 850 hPa (denoted as ‘Uwind’), and c meridional component anomalies at 850 hPa (denoted as ‘Vwind’) for the nine circulation patterns (CPs) as represented by RegIPSL-Control. The reference datasets are ERA5 for horizontal low-level winds at 850 hPa and CHIRPS for rainfall anomalies. (EPS 216 KB)

382_2023_6835_MOESM4_ESM.eps

Fig. S4 Composite time series of: a incoming shortwave radiation, b outgoing shortwave radiation, c incoming longwave radiation, d outgoing longwave radiation, over the total southern Amazon, forest and cropland areas (cyan, green and yellow lines, respectively) from RegIPSL-Control. Green and yellow envelopes represent the standard deviation for each land cover. All time series are in W m-2. Vertical cross-sections of: e potential temperature over forest areas and f forest minus crop/grass potential temperature (K), i equivalent potential temperature over forest areas (K) and j forest minus crop/grass equivalent potential temperature difference (K). The x-axis represents the time, with negative (positive) values for days before (after) the onset. (EPS 455 KB)

382_2023_6835_MOESM5_ESM.eps

Fig. S5 Taylor diagrams of the spatial patterns of: a rainfall anomalies b zonal component anomalies at 850 hPa (denoted as ‘Uwind’), and c meridional component anomalies at 850 hPa (denoted as ‘Vwind’) for the nine circulation patterns (CPs) as represented by RegIPSL-Deforested, taking as a reference dataset RegIPSL-Control. (EPS 219 KB)

382_2023_6835_MOESM6_ESM.eps

Fig. S6 Differences RegIPSL-Deforested minus RegIPSL-Control in vertically integrated moisture convergence composites for the 9 circulation patterns (CPs) defined from the k-means clustering analysis. Differences are in mm day-1. Only significant vertically integrated moisture convergence differences are shown (t-test, p<0.05). Magenta box shows the southern Amazon region (5°S-15°S, 70°W-50°W). The magenta line highlights the deforested area. (EPS 7038 KB)

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Sierra, J.P., Espinoza, JC., Junquas, C. et al. Impacts of land-surface heterogeneities and Amazonian deforestation on the wet season onset in southern Amazon. Clim Dyn 61, 4867–4898 (2023). https://doi.org/10.1007/s00382-023-06835-2

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