Large-Scale Climate Drivers of Interannual to Multidecadal Variability in Rainfall Occurrence during Indian Summer Monsoon

Abstract

Abstract Rainfall occurrence (or rainy days) during the Indian summer monsoon (ISM) exhibits a significant decline over the last century, that is considerably more widespread than the decline observed in rainfall magnitude. Here, we investigate the teleconnections of monsoon rainfall occurrence in India with prominent large-scale climate systems to examine their role in the observed widespread decline. Study results reveal strong interannual (5–12 years) periodicities in rainfall occurrence over central and western parts of north India, whereas multidecadal (30–40 years) periodicities are found dominant over northwest Himalayas, northeast India and parts of south India. El Niño-Southern Oscillations (ENSO) dominates the interannual variability and exhibits strong negative linkage with rainfall occurrence over the entire country except for northeast and parts of south India. The influence of Indian Ocean Dipole (IOD) and Pacific Decadal Oscillations (PDO) is mainly observed as modulations to ENSO’s linkage with rainfall occurrence at interannual and decadal timescales, respectively. Co-occurrence of strong (negative or positive) IOD results in supressed influence of ENSO, whereas warm (cold) PDO is associated with suppressed (enhanced) ENSO impact on rainfall occurrence. After 1950s, PDO’s linkage with rainfall occurrence has strengthened over northeast, western Himalayas, and peninsular south India, that is responsible for the observed dominance of multidecadal periodicities. IOD’s linkage with rainfall occurrence has also strengthened after 1970s over northwest, west central and parts of peninsular India leading to strong positive relationship in recent years. Further investigation suggests that the observed decline in rainfall occurrence is attributable to the shorter and less frequent La Niña events and stronger positive IOD events in the warming climate. The study findings would essentially benefit in accurate predictions and long-term projections of monsoon rainfall occurrence to facilitate planning and policy making.