The shortening of the rainy season in the Central Zagros region, as an environmental and economic challenge, has necessitated a thorough investigation into its causal mechanisms. This study aimed to analyze the relationship between global warming, the evolution of the subtropical high-pressure system, and temporal changes in the rainy season in the Central Zagros. To achieve this objective, daily precipitation data from 19 synoptic stations in the Central Zagros region (over a 35-year period, from the 1990–1991 to 2024–2025 water years), obtained from the Iranian Meteorological Organization, were utilized along with global temperature anomaly data from NASA's GISS center (1990–2024) and NCEP/NCAR reanalysis data from the U.S. National Center for Atmospheric Research (1990–2024). The research methodology combined statistical and synoptic approaches. The findings reveal that the global temperature anomaly increased by 0.83°C during the study period (from 0.45°C in 1990 to 1.28°C in 2024), which coincided with the nonlinear intensification and expansion of the subtropical high-pressure system. The geopotential height of this system at the 500-hPa level has increased by an average of about 30 meters, its spatial extent has expanded up to 27 times, and its annual persistence (Above 5800 meters) in the region has grown by approximately 126%. Statistically, this increase corresponds to an additional 97 days (rising from 77 days in the first half of the 1990s to 174 days in the mid-current decade). Quantitative analyses confirm a strong causal chain: global warming (R² = 0.53) drives the intensification of the subtropical high (correlation coefficient = 0.73), which in turn is strongly correlated with the reduction in rainy season length (correlation coefficient = –0.77). Based on the regression model, for every 0.1°C rise in global temperature, the rainy season shortens by 7.8 days. This study demonstrates that the Central Zagros region stands at the threshold of a historic hydroclimatic shift and underscores the urgent need to redesign water and agricultural management strategies in accordance with the intensified and temporally shifted seasonal pattern.