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 absolute 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 21^st century (2070–2099).

The storylines are based on changes in key physical drivers, including mid-tropospheric circulation, regional soil moisture, sea surface temperature in Niño 3.4 region, and the intensity of the South Atlantic Convergence Zone. 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 changes in the South Atlantic Convergence Zone. Central-eastern and central Argentina exhibit mixed local and remote influences, while southern regions are predominantly affected by local drivers (soil drying and atmospheric circulation changes).

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.