Abstract
Background:The varied topographical features of the Indian region are responsible for variation in distribution of rainfall over different parts of the country. More than 80% of the country’s rainfall is received during the monsoon season. Researchers noted that there is change in distribution of this monsoon rainfall associated with climate change and global warming. This changing pattern in rainfall can be investigated by seasonality index (SI) of rainfall. Such studies are essential to identify the changes in runoff, infiltration, surface and groundwater management, agricultural planning,etc.Method:The variation in seasonality in rainfall over the Indian region is examined using monthly rainfall values for the period 1951 to 2015 of 34 meteorological sub-divisions excluding two Sea Islands. A seasonality index (SI) of a monthly rainfall is computed on monthly, seasonal (June to September) and annual scale. It is observed that seasonality index of rainfall of 34 sub-divisions for all months are in the range 0.37 (Jammu & Kashmir) to 1.56 (Saurashtra Kutch & Diu).Results:The results show that rainfall is markedly seasonal with a long dry season and most rainfall in less than three months. Most of the rainfall occurs in monsoon months. The seasonality index for monsoon season is computed and it varies from 0.19 (Nagaland, Manipur, Mizoram,Tripura) to 0.59 (Saurashtra Kutch & Diu) resulting in rainfall spread throughout the year, but with a definite wetter season.Conclusion:Trends of this index through the 65-year period are identified and indicate that seasonality is increasing in Uttaranchal, Himachal Pradesh, Gujarat Region-Dadra & Nagar Haveli; Saurashtra-Kutch & Diu, Konkan & Goa, Madhya Maharashtra, Marathwada, Chattisgarh, Tamilnadu & Pondicherry. The analysis clearly showed the climate change impact on northwest sub-divisions of the country showing increase in SI values leading to dryness during the monsoon season. The negative trend in SI values was observed in Sub- Himalayan West Bengal, Haryana-Delhi-Chandigarh, Punjab, Jammu & Kashmir, West and east Rajasthan, coastal Andhra Pradesh showing increasing wetness for an already wet months although rainfall occurs in a very short period of just a month or two.
Highlights
India being an agricultural country, the analysis of rainfall variability and seasonality is important due to their tremendous influences towards agricultural water use
seasonality index (SI) of monsoon season varies from 0.0665 to 0.3529 resulting in rainfall spread throughout the year, but with a definite wetter season
India is a seventh largest South Asian country having diverse terrain giving the country a distinct geographical entity. It is bounded by the Great Himalayan ranges in the north; it stretches southwards and at the Tropic of Cancer, it has a narrow peninsular region bounded by the Indian Ocean in the south between the Bay of Bengal on the east and the Arabian Sea on the west
Summary
India being an agricultural country, the analysis of rainfall variability and seasonality is important due to their tremendous influences towards agricultural water use. Variability of rainfall may be defined as the degree to which rainfall amounts vary across an area or through time. It is an important characteristic of the climate of an area. Researchers noted that there is change in distribution of this monsoon rainfall associated with climate change and global warming. This changing pattern in rainfall can be investigated by seasonality index (SI) of rainfall. Such studies are essential to identify the changes in runoff, infiltration, surface and groundwater management, agricultural planning, etc
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