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<p>In recent decades, rainfall over the Indian landmass has decreased in June but increased from July to September, with June (September) contributing less (more) to the seasonal total, as a result of the observed shift toward early rainfall in late May followed by a June dry spell. The present paper hypothesizes that the decreasing June rainfall trend is driven by weakened atmospheric circulation, reduced moisture advection, and feeble convergence over India during this month. The reduced convection trend over India has co-occurred with increased rainfall over the northwest Pacific (NWP) and the equatorial Indian Ocean (IO). Over the recent decades, the onset of the El Niño-Southern Oscillation (ENSO) has been delayed, shifting the ENSO-Monsoon teleconnection toward July- September months. Consequently, June rainfall variability is primarily influenced by the pre-monsoon warming in the equatorial IO and the associated early propagation of monsoon onset. Additionally, the influence of North Tropical Atlantic (NTA) sea surface temperature (SST) anomalies on Indian summer monsoon rainfall (ISMR) has strengthened toward the end of the monsoon season. This evolving dynamic contributes to the contrasting rainfall anomalies observed in June compared to the July–September period.</p>

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Why Does June rainfall over India have different variability and contribution to the seasonal rainfall compared to other months during the recent period?

  • 期刊论文

  • 发表日期：

    2025年12月9日

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  • Prasanth A. Pillai,
  • K.V Suneeth,
  • V.G Kiran

摘要

In recent decades, rainfall over the Indian landmass has decreased in June but increased from July to September, with June (September) contributing less (more) to the seasonal total, as a result of the observed shift toward early rainfall in late May followed by a June dry spell. The present paper hypothesizes that the decreasing June rainfall trend is driven by weakened atmospheric circulation, reduced moisture advection, and feeble convergence over India during this month. The reduced convection trend over India has co-occurred with increased rainfall over the northwest Pacific (NWP) and the equatorial Indian Ocean (IO). Over the recent decades, the onset of the El Niño-Southern Oscillation (ENSO) has been delayed, shifting the ENSO-Monsoon teleconnection toward July- September months. Consequently, June rainfall variability is primarily influenced by the pre-monsoon warming in the equatorial IO and the associated early propagation of monsoon onset. Additionally, the influence of North Tropical Atlantic (NTA) sea surface temperature (SST) anomalies on Indian summer monsoon rainfall (ISMR) has strengthened toward the end of the monsoon season. This evolving dynamic contributes to the contrasting rainfall anomalies observed in June compared to the July–September period.