Abstract/Summary

Extreme precipitation events (EPEs) are among the most pervasive weather hazards in the western Himalayan region (WHR), posing widespread damage to life, infrastructure, and agriculture. This study investigates the synoptic and large-scale characteristics linked to winter precipitation extremes over the WHR. EPEs are identified as events surpassing the 95th percentile threshold. A composite analysis is employed using two reanalyses—ERA5 and IMDAA to elucidate the synoptic conditions conducive to EPEs. Our findings suggest that EPEs in the WHR are linked to an intensified subtropical westerly jet, characteristically shifted to south than normal. Enhanced kinetic energy in the upper troposphere, attributed to increased baroclinic instability, reinforces moisture convergence and strengthens synoptic scale circulation, triggering deep convection and supporting EPEs. Notably, the interplay of pronounced Rossby waves sinking over the region, coupled with regional orography, significantly modulates the intensity of western disturbances (WDs) during extremes. Employing clustering analysis, we observed that the strongest EPEs are linked to anomalous vorticity in the upper to middle troposphere, together with deep convection via highly strengthened WDs, suggesting a potential role of large-scale influences. Using Lagrangian method, we identify that Arabian Sea is primary moisture source for EPEs in WHR. We further delved into the role of large-scale connections and EPEs through quasi-resonant amplification (QRA) analysis in the WHR using ERA5 data. The findings unveil the association of QRA with notably magnified, quasi stationary mid-latitude planetary waves characterized by wavenumbers 6/7/8 (baroclinic waves), contributing to precipitation extremes. Remarkably, distinct fingerprints of meridional temperature gradients, indicative of QRA, are linked to EPEs. Furthermore, this investigation discerns distinctive QRA patterns associated with varying clusters of extreme event intensities. Overall, our results emphasize the crucial role of QRA in amplifying planetary waves and promoting extreme precipitation in the WHR, underscoring the vulnerability of the region to evolving climate conditions and providing insights into the underlying physical mechanisms.