Projecting climate change in South America using variable-resolution Community Earth System Model: An application to Chile

We introduce variable-resolution enabled Community Earth System Model (VR-CESM) results simulating historical and future climate conditions at 28 km over South America and 14 km over the Andes. Three 30-year simulations are performed: a historic (1985-2014), a near future (2030-2059), and an end-century (2070-2099) simulation under the RCP8.5 scenario. Historic results compare favourably to several temperature and precipitation reanalysis products, though local biases are present, particularly during austral summer. Future simulations highlight broad warming patterns (+3-6 degrees C by end-century) and heterogeneous precipitation responses across South America that qualitatively agree with prior modelling efforts. Our results reveal that the interaction between temperature and precipitation changes produce shifts in several Koppen-Geiger climates. Notable changes include the near-elimination of the Andean Tundra or Alpine climates, a 15% decrease in Tropical Rainforests and a Tropical Savannah expansion of 20%. To provide a regionally focused analysis of projected climate change and to illustrate the benefits of variable resolution modelling, we analyse changes in the magnitude and trend in seasonal and daily temperature and precipitation in Chile. We also examined several metrics [e.g., snow water equivalent (SWE), temperatures on wet days, and days below 0 degrees C] to evaluate potential impacts of climate change on the Chilean cryosphere between the end-of-century and historic periods, finding wide-ranging indications of cryospheric decline. These changes are interpreted through reductions in the timing (1-2.5 months earlier peak SWE) and magnitude (200-1,000 mm SWE decreases) of water stored as snow in the Andes, a 10-30% decrease in number of cool season wet days with temperatures below 1 degrees C, and 50-200 fewer days (annually) with minimum temperatures below 0 degrees C. Our aim in producing a high-resolution dataset of climate projections from VR-CESM is to support analyses of climate change throughout South America but especially in vulnerable montane regions and to provide additional results for comparison with previous, ongoing, and upcoming modelling efforts.