Storylines of extreme summer temperatures in southern South America

Understanding the sources of uncertainty in future climate extremes is crucial for effective regional adaptation strategies. This study uses simulations from 26 global climate models to investigate projections of summer maximum temperature (TXx) across four southern South America regions: northern, central-eastern, and southern areas, and central Argentina. A storyline approach is applied to examine how different climate drivers interact to shape TXx changes by the late 21st century (2070–2099).

The storylines are based on changes in key physical drivers, including mid-tropospheric ridging, regional soil moisture, sea surface temperature in Niño 3.4 region and an OLR gradient index that reflects changes in atmospheric stability and the positioning of convective activity over the South Atlantic Ocean. A multi-linear regression framework shows that dominant drivers of projected TXx warming differ across regions. In northern areas, uncertainty is primarily controlled by remote influences, including tropical sea surface temperatures and OLR variations over the subtropical South Atlantic Ocean. Central-eastern areas and central Argentina show a combination of local and remote drivers, whereas southern regions are mostly governed by local factors, such as soil drying and atmospheric blocking. Together, these drivers account for up to 56% of the inter-model spread in regional TXx projections. Nonetheless, their capacity to capture the projected spread in percentile-based indices and regional heatwaves attributes is limited, suggesting that the drivers of heatwave responses vary with the metric.