Monsoon dynamics and future projections in the Himalaya: Insights into sea surface temperature, sea level pressure relationships, and future flood risks

The Himalaya influences the fundamental features of the Indian Summer Monsoon (ISM) circulation across South Asia. Reliable predictions of ISM dynamics require an improved understanding of the relationship with the El Niño–Southern Oscillation (ENSO)–sea surface temperature (SST) and Sea Level Pressure (SLP) relationships in the Niño region. To address this, we conducted a detailed analysis of teleconnections, correlations, regime shifts, periodicity, and return periods of monsoons over the Karakoram Himalaya (KH), Western Himalaya (WH), Central Himalaya (CH), and Eastern Himalaya (EH) using gridded precipitation, ENSO-SST, and SLP data across the Niño 4, 3.4, and 3 regions. Additionally, we examined Coupled Model Intercomparison Project phase 5 (CMIP5) projections considering evolving relationships. The findings show that the monsoons over the CH, WH, EH, and KH have stronger, moderate, weaker, and weakest spatial correlations, respectively, with the SST of Niño regions. Notably, the SST anomalies for the Niño regions 4 and 3.4 reveal distinct regime shift for the years 1977 C.E. and 1990 C.E., however, Niño regions 3 and 1 + 2, do not exhibit any such shift. The SST anomalies for the Niño 3.4 and Niño 4 from 1977 to 2019 C.E., and 1990–2019 C.E., were 0.087°C and 0.060°C, respectively, indicating systematic warming of the sea surface. This warming trend is further linked to projections from CMIP5 RCP 4.5 and RCP 8.5, which suggest that the EH region may experience significant flooding during the monsoon months by 2100 due to high and extreme precipitation.