Climate indices change during 21st century in high-resolution RCMs

The Antarctic is a critical component of the global atmosphere-ocean-cryosphere interaction and is simultaneously one of the regions most sensitive to climate change. However, the response to climate change varies significantly across the continent. Therefore, it is crucial to understand how the Antarctic will be impacted by climate change during the 21st century.

The aim of the study is to define general features of climate change in the Antarctic based on climate indices simulated by  regional climate models (RCMs). We used WCRP standard climate indices: frost days (number of days with a daily minimum temperature  < 0°C),  ice days (number of days with a maximum temperature < 0°C), total annual precipitation, longest consecutive wet spell (number of consecutive days with >1 mm/day), longest dry spell (number of consecutive dry days <1 mm/day), simple precipitation intensity (annual precipitation divided by wet days), intense, heavy and extreme precipitation for the daily precipitation amounts (90th, 95th and 99th percentiles respectively). Indices were computed from three RCMs (HCLIM, MAR, RACMO) under the two storylines: (1) strong sea ice decrease and weak strengthening of the southern polar vortex; (2) weak sea ice loss but strong polar vortex strengthening. Results were compared across three periods: 1986–2005 (historical), 2041–2060 (mid-century), and 2081–2100 (end-of-century). Models results and further postprocessing were performed under Horizont2020 PolarRES and OCEAN ICE Projects.

A comparison of climatic indices from historical to the end of the century reveals a significant transition toward a warmer and wetter climate. These changes are most pronounced in the coastal regions and the Antarctic Peninsula, while the high-elevation interior remains relatively stable. Dramatic reduction in 'Ice Days' particularly on the Peninsula is projected. This reduction implies a substantial increase in surface melt potential and an extended thaw season, accompanied by a corresponding—though less severe—decrease in 'Frost Days'.

Simultaneously, the models project a clear increase in total annual precipitation, primarily over the Southern Ocean and coastal zones. Precipitation characteristics also shift, exhibiting increased daily intensity and a modest decrease in the length of 'Consecutive Dry Days' over the continental interior.

Precipitation extremes (99 th percentile) are heavily concentrated along the Antarctic Peninsula and coastal West Antarctica. In regions with significant orographic enhancement, localized intensities exceed 100 mm/day, whereas the interior plateau remains much less (<10 mm/day). 

Overall, both storylines illustrate a fundamental shift in the Antarctic climate during the 21st century—particularly in coastal zones—characterized by a longer, more intense melt season and hydrological cycle. These changes hold significant implications for ice shelf stability and overall ice-sheet mass balance.