Eccles et al. (2025) High-resolution downscaled CMIP6 drought projections for Australia

Identification

• Journal: Hydrology and earth system sciences
• Year: 2025
• Date: 2025-09-29
• Authors: Rohan Eccles, Ralph Trancoso, Jozef Syktus, Sarah Chapman, Nathan Toombs, Hong Zhang, Shaoxiu Ma, Ryan McGloin
• DOI: 10.5194/hess-29-4689-2025

Research Groups

• Climate Projections and Services, Queensland Treasury, Queensland Government, Brisbane, QLD, Australia
• School of The Environment, The University of Queensland, Brisbane, QLD, Australia

Short Summary

This study investigates the impacts of climate change on meteorological droughts across Australia using a high-resolution ensemble of downscaled CMIP6 climate models under three Shared Socioeconomic Pathway (SSP) scenarios. It projects consistent increases in drought frequency, duration, spatial extent, and percent time in drought, particularly for southern Australia and when considering evapotranspiration, indicating a significant shift towards more extreme climatic conditions under higher emissions.

Objective

• To assess changes in future projected meteorological droughts, including the frequency of occurrence, duration, spatial extent, and percent time in drought estimated using the Standardised Precipitation Index (SPI) and the Standardised Precipitation Evapotranspiration Index (SPEI).
• To compare changes in droughts between three different emissions pathways (SSP126, SSP245, SSP370), two categories of drought severity (moderate to extreme, and extreme), and two drought indices (SPI, SPEI).
• To evaluate how different climatic regions of the Australian continent are projected to experience future droughts under three different emissions pathways and estimate the time of emergence for significant shifts to occur.

Study Configuration

• Spatial Scale: Entire Australian continent, evaluated at a 10 km resolution. Analysis conducted across four Natural Resource Management (NRM) super-clusters (Eastern Australia, Northern Australia, the Rangelands, and Southern Australia), with supplementary datasets tailored for 566 Australian local government areas and 219 river basins.
• Temporal Scale: Historical period (1981–2010) for calibration and validation. Future projections assessed for the 2050s (2041–2060) and 2090s (2081–2100) relative to a 1995–2014 reference period. Time series analysis extends from 1981 to 2100.

Methodology and Data

• Models used:
  • Conformal Cubic Atmospheric Model (CCAM) developed by CSIRO for dynamical downscaling.
  • Ensemble of 60 high-resolution dynamically downscaled CMIP6 climate model simulations (15 historical, 45 future) derived from 11 different CMIP6 Global Climate Models (GCMs).
  • Drought indices: Standardised Precipitation Index (SPI) and Standardised Precipitation Evapotranspiration Index (SPEI), both calculated with a 12-month accumulation period.
  • Potential Evapotranspiration (PET) for SPEI calculation derived offline using the Penman–Monteith reference crop equation from daily CCAM outputs.
• Data sources:
  • CMIP6 GCMs (e.g., ACCESS-ESM1.5, ACCESS_CM2, CMCC-ESM2, CNRM-CM6-1-HR, EC-Earth3, FGOALS-g3, GFDL-ESM4, GISS-E2-2-G, MPI-ESM1-2-LR, MRI-ESM2-0, NorESM2-MM).
  • Queensland Future Climate Projections 2 (QldFCP-2) dataset (10 km resolution over Australia).
  • Observational data (1980–2010) for validation: Daily gridded precipitation data (0.05° resolution) from the Australian Gridded Climate Data Project (AGCD). Daily gridded PET data (0.05° resolution) from the Australian Water Outlook.
  • Shared Socioeconomic Pathway (SSP) scenarios: SSP126 (low emissions), SSP245 (moderate emissions), and SSP370 (high emissions).

Main Results

• Consistent increases in drought frequency, duration, percent time, and spatial extent were projected for southwest Western Australia, southern Victoria, southern South Australia, and western Tasmania using both SPI and SPEI.
• SPEI-derived droughts showed significantly larger increases and were projected to increase consistently across most of Australia, reflecting the additional impact of increased evapotranspiration.
• Increases in drought conditions primarily occurred at the expense of "normal" climatic conditions, with similar or increased time spent under extreme wet conditions, indicating an overall shift towards more extreme climatic conditions.
• The largest increases in drought were projected for the end of the century (2090s) and under the high-emissions scenario (SSP370).
• For SPEI, a 10% shift towards drier conditions was reached by approximately 2040 for the Rangelands and Southern Australia, and a 20% shift by approximately 2060. These shifts were delayed in Northern Australia and Eastern Australia to approximately 2060 and 2090, respectively.
• Under the high-emissions scenario (SSP370) by the end of the century, the area subject to extreme drought in Southern Australia was projected to be 2.8 times greater than low-emissions using SPI, and 4 times greater using SPEI.
• Cutting emissions from high to low levels by the end of the century would decrease the area affected by extreme droughts (SPEI-derived) by a factor of 4 in Southern Australia, 3.2 in the Rangelands, 1.9 in Northern Australia, and 2.8 in Eastern Australia.

Contributions

• This study utilizes the largest downscaled ensemble of CMIP6 projections for Australia (60 simulations from 11 GCMs) at an unprecedented 10 km resolution, providing enhanced regional climate granularity.
• It provides high-resolution drought projections tailored to Australian local government areas and river basins, offering valuable, granular data for local and regional adaptation planning and decision-making.
• The research highlights the critical role of potential evapotranspiration (PET) in future drought projections, demonstrating that SPEI consistently projects greater and more widespread increases in drought compared to SPI, especially in arid/semi-arid regions and under high-emission scenarios.
• It reveals a significant shift in Australia's climate towards more extreme conditions, with an increase in both extreme drought and extreme wetness at the expense of near-normal conditions.

Funding

• Queensland Future Climate Science Program (QFCSP)
• National Partnership for Climate Projections

Citation

@article{Eccles2025Highresolution,
  author = {Eccles, Rohan and Trancoso, Ralph and Syktus, Jozef and Chapman, Sarah and Toombs, Nathan and Zhang, Hong and Ma, Shaoxiu and McGloin, Ryan},
  title = {High-resolution downscaled CMIP6 drought projections for Australia},
  journal = {Hydrology and earth system sciences},
  year = {2025},
  doi = {10.5194/hess-29-4689-2025},
  url = {https://doi.org/10.5194/hess-29-4689-2025}
}