Assessing the Impact of the South Indian Ocean High‐Pressure System Using a Novel Index

ABSTRACT The South Indian Ocean High‐Pressure (SIOHP) system plays a crucial role in modulating atmospheric circulation, precipitation, and temperature patterns across the Indian Ocean basin and adjacent regions. Despite its significance, a comprehensive index for quantifying SIOHP variability, intensity, and impacts has been lacking. To address this gap, this study utilises a novel SIOHP index to systematically assess its climatic influence. Our findings reveal that the SIOHP's seasonal variability significantly impacts regional precipitation, temperature, and humidity. During austral winter (JJA), a stronger SIOHP is associated with drier and cooler conditions in southeastern Africa and Madagascar, while its weakening in summer (DJF) corresponds to increased precipitation in these regions. Additionally, a westward shift of the SIOHP enhances rainfall in southwestern Australia, mitigating drought conditions. Furthermore, the SIOHP‐driven moisture transport plays a vital role in shaping regional hydroclimate variability, influencing moisture advection and precipitation. These findings highlight the SIOHP's critical role in regional climate variability, underscoring the need for further research on its drivers and interactions with larger climate modes. This study provides a quantitative framework for improving seasonal forecasting, climate adaptation planning, and early warning systems in a changing climate.