Argentina Breaks Heat Records in the 2022/23 Warm Season: Influence of Synoptic Circulation, Local Feedbacks, and Climate Change

The summer of 2022/23 in Argentina marked an unprecedented period with 10 heat wave events (HWs), primarily affecting the central region. This study characterises the four most extensive HWs of that season through synoptic, thermodynamic, and attribution analyses. Regarding the synoptic conditions, we find that mid-level anticyclonic anomalies were essential for the occurrence of these HWs. Although they exhibited different characteristics, the high-pressure system was quasi-stationary in three of them, while it was transient in the other one. This atmospheric pattern interacted with the South Atlantic Convergence Zone and the South American Low-Level Jet, and played a fundamental role in the amplification of the HWs, providing a warming of ~+2°C (compared to what would be obtained by a random circulation). The terms of the thermodynamic equation reveal that diabatic processes were the main drivers of daily temperature changes in the analysed HW events. Horizontal advection also made an important (albeit secondary) contribution, particularly during a tropical air mass intrusion over central and northern Argentina. Local feedbacks were also important for understanding the events. North-central Argentina is a region of strong land-atmosphere coupling, and all HWs were preceded by soil moisture deficits impinged by three consecutive La Niña years. Using the flow-analogue technique, we quantify that the contribution of dry soils to warming was ~1°C (with respect to that of wet soils), suggesting that soil moisture deficits caused an increase in sensible heat fluxes and amplification of warming. Finally, we find that recent climate change has also exacerbated HW intensities by +0.5 to +1.2°C. Atmospheric circulation patterns similar to those observed during the events cause warmer conditions in the present than in the past, mostly due to temperature trends rather than changes in the intensity of weather systems. Our analysis reveals that the exceptionally high temperatures were a result of various factors, including the rare occurrence of a three-year La Niña-induced drought. Recent studies suggest that consecutive La Niña events may become more common due to climate change. Northeastern Argentina would be particularly affected by this shift due to its large response to ENSO and land-atmosphere interaction. Additionally, ongoing temperature trends are expected to accelerate, contributing to the intensification of HWs. Consequently, it is expected that similar extreme summers become more frequent in the 21st century.