Abstract
India observes the summer monsoon in June–July–August–September (JJAS) season, and the livelihood security of a huge population depends on it. The impact of the monsoon onset timing, length of monsoon season, rainfall amount, and related extreme events is huge on the Indian economy. Therefore, understanding the inherent intricacies needed a detailed investigation. In five homogenous monsoon regions of India, the trend of monsoon onset and the length of monsoon season are examined. The association between 1) monsoon onset ∼ rainfall amount, 2) length of monsoon season ∼ rainfall amount, and 3) monsoon onset ∼ length of monsoon season is investigated. Subsequently, the behavior of rainfall and extreme excess days in the ±1 standard deviation (SD) length of monsoon season is also examined in detail. The trend for monsoon onset shows late onset in all the homogenous monsoon regions except the northeast region. The length of monsoon season is found increasing significantly with high magnitude in west central and northwest regions. A significantly strong negative correlation (∼−0.6) for monsoon onset timing ∼ length of monsoon season is observed. Therefore, the change in rainfall anomaly, extreme excess days, and rainy days is done concerning the length of the monsoon season. In the cases of the −1 SD (+1 SD) length of monsoon season, rainfall anomaly and extreme excess days are low (high) in most parts of the homogenous monsoon regions. Extreme excess days showed a significant association with rainy days, which indicates a high possibility of rainy days converting into extreme excess days. However, the increase in extreme excess days in the +1 SD length of monsoon season is limited to a great extent in JJAS and June only. Morlet wavelet power spectrum shows the delay (advance) of power in −1SD (+1 SD) length of monsoon season.
Highlights
IntroductionThe onset of monsoon has always been an important phenomenon for any region with a monsoon climate across the globe
JJAS is generally defined as the monsoon season in India because the major chunk of the summer monsoon rainfall amount is obtained during this period of the year (Sahu et al, 2020; Saini et al, 2020; Saini and Sahu, 2021)
In different homogenous monsoon regions, the significant strong negative correlation (~−0.6) between the monsoon onset and the length of monsoon season reveals that the early onset leads to a large length of monsoon season
Summary
The onset of monsoon has always been an important phenomenon for any region with a monsoon climate across the globe. India is a tropical country with the summer monsoon season in June–July–August–September (hereafter JJAS). JJAS is generally defined as the monsoon season in India because the major chunk of the summer monsoon rainfall amount is obtained during this period of the year (Sahu et al, 2020; Saini et al, 2020; Saini and Sahu, 2021). India has a huge dependence on the behavior of the monsoon system from its onset to withdrawal (Prasad and Hayashi, 2005; Wang et al, 2021). It is an agriculturally dominant country with large size of its population engaged in agriculture-based activities for livelihood and food security (Pingali et al, 2019; Kaur et al, 2021). Early or late monsoon has always been a point of discussion among agronomists, meteorologists, economists, and policymakers
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