Changes in the South Pacific High intensity since the mid-20th century: implications and environmental impacts in the Mediterranean and South-Central Chile

The South Pacific High (SPH) plays a crucial role in shaping the climate of South America by influencing atmospheric and oceanic processes in Chile, such as upwelling, precipitation regime, and affecting the frequency of extreme climate events like heatwaves and extreme wildfires in the Mediterranean (30º-36ºS; MCh) and South-Central Chile (37º-42ºS; SCCh). Despite the relevance of SPH on the Chilean and South American climate at different time scales, its temporal Intensity changes have been partially understood to date. Here, we used monthly mean sea level pressure data from ERA5, spanning 1940 to 2024, to estimate the monthly SPH intensity (SPHI) following Barrett and Hameed (2017). We consider the annual year from January to December months, while summer is taken from the previous December to the current February, March to May as autumn, June to July as winter, and September to November as Spring. We examined annual and seasonal trends in SPHI and explored the relationships between gridded products of precipitation (Pr), minimum (Tn), and maximum temperatures (Tx) derived from the Centre for Climate and Resilience Research CR2 at 5 km. In addition, monthly surface soil moisture (SSM) from ERA5 has also analyzed with the SPHI. We computed Pearson correlations between the SPHI and the environmental variables during 1961-2024. Our findings indicate a significant increasing trend (p-value < 0.01) in the SPHI at annual and seasonal scales since 1940. In addition, Pearson correlations indicate a significant and negative relationship between SPHI and Pr and Tn at annual and all-year seasons in both sub-regions. The linkages between SPHI and Tx and SSM recorder significant and negative correlations during winter and spring in both sub-regions. Our results indicate severe changes in the SPHI on annual to seasonal scales, and also remark the strong modulation of the SPHI on Pr regime in both sub-regions. Furthermore, also reveals the relevance of the SPHI on the Tn modulation at annual and seasonal scales. Finally, relationships between SPHI and SSM in the spring are crucial to understanding, given the previous development of favourable fire conditions associated with wildfire dynamics and drought conditions in both Chilean sub-regions.