Long-term rainfall variability of Indian river basins in the context of global warming and climatic indices

ABSTRACT

The interannual variability in Indian summer monsoon rainfall (ISMR) results from numerous multi-scale interrelated phenomena. Using reconstructed rainfall data from 1813 to 2020 for 20 river basins in India, the research reveals a substantial decline in the Ganga, Brahmaputra, Cauvery, Brahmani, Pallar, andPonniyar ranging from 6.6 to 19.7%, and a notable increase of 7.9% in Surma in past two decades compared to the last century. Despite significant regional disparities, a modest increase of 1.3% in ISMR is observed over 101 years, indicating long-term stability. Spectral analysis highlights the dominance of short-term fluctuations (75%) in interannual variability. The evolving relationships between rainfall and global climatic indices are underscored. The Southern Oscillation Index (SOI), Arctic Oscillation (AO), Niño3.4, and Pacific Decadal Oscillation (PDO) are the most influential indices across basins, mostly showing a stronger relationship in June and September compared to July and August. Over time, AO and SOI maintained a significant positive relationship and Niño3.4 inverse relationship with ISMR, while the AO-ISMR link weakened post-1980s indicating a shift in traditional teleconnections with climate change. Northern and eastern basins exhibit strong correlations with the warming over eastern and central Afro-Asian highlands, while southern basins are influenced by equatorial climate dynamics. The findings emphasize the need for region-specific model predictions and localized adaptive water management strategies.