Variability in Indian monsoon onset: Delays, advances, and regional disruptions

The Indian Summer Monsoon is a critical climatic phenomenon that sustains agriculture, water resources, and economic stability across South Asia. Accurate prediction of monsoon onset timing is essential, as delays can severely disrupt agricultural cycles, reduce crop yields, and strain water availability. This review examines the factors driving monsoon onset variability, with particular emphasis on delayed onset patterns and their regional impacts. The ISM onset is governed by complex atmospheric transitions including the weakening of westerlies, strengthening of easterlies, and formation of onset vortices that are modulated by large-scale climate drivers. El Niño–Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), and Madden–Julian Oscillation (MJO) phases play dominant roles in determining onset timing. Climate change has intensified these interactions by amplifying ENSO variability, altering IOD behavior, and weakening atmospheric circulation responses, thereby increasing the complexity of monsoon dynamics. Additionally, rising Land Surface Temperatures (LST) driven by global warming and land use changes have further contributed to onset variability. Historical analysis reveals that late-onset events were particularly frequent during 1900–1925 and 1970–1990, though some regions now experience earlier onsets, reflecting spatiotemporal heterogeneity in monsoon behavior. Advances in forecasting particularly through Artificial Neural Networks (ANNs) and Multi-Model Ensemble (MME) approaches—have enhanced prediction accuracy by capturing both deterministic and stochastic rainfall patterns while reducing model uncertainties. Integration of indigenous knowledge into forecasting frameworks offers valuable localized insights for climate adaptation. Agricultural resilience strategies, including climate-smart practices such as integrated soil fertility management, agroforestry, resource conservation techniques, and community-based adaptation programs, are crucial for mitigating the impacts of monsoon variability while simultaneously contributing to greenhouse gas mitigation. Given the escalating complexities introduced by climate change, a synergistic approach combining improved forecasting models with adaptive agricultural practices is essential to enhance preparedness, optimize resource management, and mitigate the socioeconomic and environmental risks associated with monsoon variability.