Storylines of extreme summer temperatures in southern South America

Abstract. Understanding the sources of uncertainty in future climate extremes is crucial for developing effective regional adaptation strategies. This study examines projections of summer maximum temperature (TXx) over four regions of southern South America: northern, central-eastern, central Argentina, and southern areas. We analyse simulations from 26 global climate models and apply a storyline approach to explore how different climate drivers combine to shape future changes in TXx for 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 phenomena over the South Atlantic Ocean. A multi-linear regression framework reveals that the dominant drivers of the projected warming in TXx vary substantially across regions. In northern areas, warming is primarily influenced by remote drivers such as tropical sea surface temperatures and OLR changes in the subtropical South Atlantic. The central-eastern and central Argentina regions exhibit mixed local and remote influences, while southern areas of South America are predominantly affected by changes in local drivers (soil drying and atmospheric blocking). Together, these drivers explain up to 56 % of the inter-model spread in future projections of TXx. However, their ability to account for the uncertainty in percentile-based indices and regional heatwave characteristics is more limited, suggesting that complex heat metrics may be influenced by additional processes.