Blanco et al. (2025) Changes in drylands in Argentina during the phases of the Pacific Decadal Oscillation (1961–2022)

Identification

• Journal: Earth Systems and Environment
• Year: 2025
• Date: 2025-11-28
• Authors: Pedro S. Blanco, Moira E. Doyle
• DOI: 10.1007/s41748-025-00940-4

Research Groups

• Facultad de Ciencias Exactas y Naturales, Departamento de Ciencias de la Atmósfera y los Océanos (DCAO), Universidad de Buenos Aires, Argentina
• CONICET – Centro de Investigaciones del Mar y la Atmósfera (CIMA), Argentina
• Instituto Franco–Argentino de Estudios sobre el Clima y sus Impactos (IFAECI) – IRL 3351, CNRS–CONICET–IRD–UBA, Argentina

Short Summary

This study investigates dryland changes in Argentina between 1961 and 2022 in relation to Pacific Decadal Oscillation (PDO) phases. It finds that drylands expand during negative PDO phases and contract during positive phases, primarily in central Argentina, driven by shifts in precipitation and evapotranspiration linked to South Pacific atmospheric circulation.

Objective

• To examine the temporal changes in drylands in Argentina during the 1961–2022 period and explore the possible relationship between these changes and the Pacific Decadal Oscillation (PDO) phases and their associated atmospheric circulation.

Study Configuration

• Spatial Scale: Continental Argentina, with a focus on central Argentina and Patagonia. Climate data was resampled to a 0.16° × 0.16° grid resolution.
• Temporal Scale: 1961–2022 (62 years), analyzing monthly data for interannual, multiannual, and quasi-decadal oscillations.

Methodology and Data

• Models used:
  • Thornthwaite method for estimating potential evapotranspiration.
  • Blackman–Tukey method with Hamming smoothing for spectral analysis.
  • Continuous wavelet transform with Morlet function for wavelet analysis (using wt function from biwavelet R package).
• Data sources:
  • Monthly mean temperature and total precipitation: Climatic Research Unit (CRU) database version 4.06 (0.5° × 0.5° resolution, bilinearly interpolated to 0.16° × 0.16°).
  • Pacific Decadal Oscillation (PDO) index: National Centers for Environmental Information (NCEI/NOAA), derived from ERSST v5.
  • Atmospheric circulation variables (vertical velocity at 500 hPa, sea surface temperature, mean sea-level pressure, zonal and meridional wind at 850 hPa and 200 hPa, geopotential height at 500 hPa, air temperature at 200 hPa): ERA5 reanalysis.
  • Dryland classification: United Nations Convention to Combat Desertification (UNCCD) criteria based on the United Nations Environment Programme (UNEP) Annual Aridity Index (AI = PRE/PET).

Main Results

• Drylands in Argentina exhibit oscillations at various frequencies, with quasi-decadal cycles (9 years) being the most prominent.
• An inverse correlation (Pearson's r = -0.15) was observed between the PDO index and total dryland extent, with the strongest and statistically significant correlation for semiarid lands (r = -0.38, p < 0.004). Arid lands showed a positive correlation (r = 0.21).
• During negative PDO phases, drylands expand by an average of 0.89% of the country's total area, driven by decreased precipitation and increased evaporative demand.
• During positive PDO phases, drylands contract by an average of 0.83% of the country's total area, driven by increased precipitation and reduced evaporative demand.
• The most significant dryland changes occur in central Argentina, where drylands advance eastward during negative PDO phases and retreat westward during positive PDO phases.
• Southern Patagonia shows an opposite pattern: decreased water deficit during negative PDO phases (due to simultaneous increases in precipitation and potential evapotranspiration) and increased water scarcity during positive PDO phases.
• The arid climate has expanded in Patagonia and the central-western region of Argentina, irrespective of PDO phases.
• Atmospheric circulation during negative PDO phases is characterized by widespread South Pacific cooling, strengthening of the Subtropical High and Subpolar Lows, weakening of the Subtropical Jet, and intensification of the Polar Jet, promoting a more zonal circulation. Positive PDO phases show reversed patterns.

Contributions

• This study provides the first integrated analysis of long-term dryland changes in Argentina specifically linked to the Pacific Decadal Oscillation phases and their associated atmospheric circulation patterns.
• It identifies and quantifies the regional variations in dryland expansion and contraction across Argentina, highlighting distinct behaviors in central Argentina and southern Patagonia.
• The findings offer a crucial scientific basis for monitoring drylands and developing climate-adaptive land management and national-scale planning strategies in vulnerable regions.

Funding

• National Council of Scientific and Technological Research of Argentina (PIP grant KE2 11220210100752CO).

Citation

@article{Blanco2025Changes,
  author = {Blanco, Pedro S. and Doyle, Moira E.},
  title = {Changes in drylands in Argentina during the phases of the Pacific Decadal Oscillation (1961–2022)},
  journal = {Earth Systems and Environment},
  year = {2025},
  doi = {10.1007/s41748-025-00940-4},
  url = {https://doi.org/10.1007/s41748-025-00940-4}
}