Abstract/Summary

In this study, we investigate the complex relationship between western disturbances (WDs), the El Niño Southern Oscillation (ENSO), and extreme precipitation events (EPEs) in the Western Himalayas (WH) during the extended winter season (November-March). WDs west of WH coincide with 97% of recorded EPEs, contributing substantially (32% in winter, 11% annually) to total precipitation within WH. Our analysis reveals that WDs co-occurring with EPEs are significantly more intense and associated with much stronger moisture transport than WDs that do not cause EPEs. EPE frequency and intensity are sensitive to ENSO phase, with EPE frequency doubling during El Niño. We find a substantial southward shift (~180 km) of the subtropical jet axis during El Niño, bringing WD tracks further south, towards their primary moisture source, the Arabian Sea. This significantly increases moisture supply to WH (which is 17% higher during El Niño), intensifying regional precipitation extremes during extreme El Niño periods. Analyzing WD-centered composites confirms a direct link between southward-shifted WDs, their proximity to the Arabian Sea, increased moisture supply, and increased regional extreme precipitation during El Niño. Overall, this study demonstrates the impact of ENSO phases on background atmospheric circulation and moisture conditions over South Asia, and establishes a direct link between alterations in the winter jet stream and moisture convergence and hence occurrences of EPEs over WH.