<p>Indian Summer Monsoon is highly susceptible to extreme rainfall events, which vary markedly across different regions. The complex topography of the country further complicates the interpretation of regional disparities in these extremes and their underlying drivers. This study investigates the regional variability of monsoon behavior across four climatically homogeneous zones: Southwest India (SWI), Southeast India (SEI), Central India (CI), and Northwest India (NWI). We analyze the frequency of extreme rainfall events, defined at the 99.9th percentile (R99.9), and explore the underlying physical mechanisms for these occurrences. To better understand the thermodynamic influences, Clausius–Clapeyron (CC) scaling is performed to assess the relationship between atmospheric moisture-holding capacity and surface temperature across the zones. Our results indicate a significant increase in extreme rainfall events over the past four decades in all regions except CI, which exhibits a slight decline in recent decades. These events are predominantly associated with large-scale precipitation, suggesting a strong influence of synoptic systems. Notably, SEI is an exception, where convective precipitation plays a dominant role, highlighting the importance of convection in this region. Furthermore, the vertically integrated moisture transport (VIMT), specific humidity, and vertical velocity (omega), along with the convective processes, were investigated. A nonlinear, region-specific relationship between total column water vapor (TCWV) and surface temperature has been observed suggesting that atmospheric dynamics plays a dominant role in modulating the extreme rainfall. The findings offer critical insights for enhancing regional monsoon predictability and inform strategies for improved societal and environmental resilience.</p>