Interannual-Decadal Hydroclimatic Variability in the Southern Himalaya Over the Past 500 Years: Mechanisms From MADA-PHYDA Integration

Understanding the drivers of interannual-to-decadal hydroclimatic variability in the southern Himalaya (SH) has been constrained by the scarcity of long-term, spatially comprehensive proxy records and data assimilation products. Here, we combine the Monsoon Asia Drought Atlas (MADA) and the Paleo Hydrodynamics Data Assimilation (PHYDA) to investigate the SH hydroclimatic variability and its mechanisms over the last 500 years (1500–2000 CE). We find that the SH hydroclimate exhibits robust interannual (2–8 years) and multidecadal (50–60 years) variability. Interannual variability is strongly associated with the coupled negative phase of El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole, producing a hydroclimatic dipole with the Indian monsoon region that diverts moisture and induces drying in the SH. Our 500-year perspective suggests that the hydroclimatic teleconnection is non-stationary, with external forcing (such as solar minima and clustered volcanic eruptions) potentially modulating teleconnection stability in a complex, context-dependent manner. The 50–60-year cycle is linked to a combined Pacific climate pattern combining Pacific Decadal Variability (PDV) and tropical sea surface temperature anomalies, with positive PDV-La Niña phases favoring reduced regional moisture transport. SH hydroclimate is positively correlated with Yarlung Zangbo-Brahmaputra River (YZBR) runoff, with correlation coefficients (r) of 0.75 (upstream) and 0.53 (downstream) (p < 0.001). Notably, the early 21st-century aridification trend remains within the historical range, although its attribution requires consideration of both internal variability and external forcing. These findings enhance our understanding of SH hydroclimatic mechanisms and provide a paleoclimatic framework to support regional climate prediction and water resource management in the region.