Analysis of long-term rainfall trends in India

Abstract

The study of precipitation trends is critically important for a country like India whose food security and economy are dependent on the timely availability of water. In this work, monthly, seasonal and annual trends of rainfall have been studied using monthly data series of 135 years for 30 sub-divisions (sub-regions) in India. Half of the sub-divisions showed an increasing trend in annual rainfall, but for only three (Haryana, Punjab and Coastal Karnataka), this trend was statistically significant. Similarly, only one sub-division (Chattisgarh) indicated a significant decreasing trend out of the 15 sub-divisions showing decreasing trend in annual rainfall. In India, the monsoon months of June to September account for more than 80% of the annual rainfall. During June and July, the number of sub-divisions showing increasing rainfall is almost equal to those showing decreasing rainfall. In August, the number of sub-divisions showing an increasing trend exceeds those showing a decreasing trend, whereas in September, the situation is the opposite. The majority of sub-divisions showed very little change in rainfall in non-monsoon months. The five main regions of India showed no significant trend in annual, seasonal and monthly rainfall in most of the months. For the whole of India, no significant trend was detected for annual, seasonal, or monthly rainfall. Annual and monsoon rainfall decreased, while pre-monsoon, post-monsoon and winter rainfall increased at the national scale. Rainfall in June, July and September decreased, whereas in August it increased, at the national scale.Key words climate change; precipitation; rainfall trend; sub-division; non-parametric test; Mann-Kendall test; India Analyse des tendances pluviométriques de long terme en Inde Résumé L'étude des tendances de précipitation est très importante pour un pays comme l'Inde dont la sécurité alimentaire et l'économie dépendent de la disponibilité temporelle de l'eau. Dans ce travail, les tendances des précipitations mensuelles, saisonnières et annuelle ont été étudiées à partir des séries de données mensuelles de 135 années (1871-2005) de 30 sous-divisions (sous-régions) de l'Inde. La moitié de ces sous-divisions présente une tendance croissante de la précipitation annuelle, mais cette tendance n'est statistiquement significative que pour trois d'entre elles (Haryana, Punjab et Karnataka littoral). De même, une seule sous-division (Chattisgarh) présente une tendance décroissante significative parmi les 15 sous-régions qui présentent une tendance décroissante de la précipitation annuelle. En Inde, les mois de mousson de Juin à Septembre contribuent à plus de 80% de la précipitation annuelle. Pendant Juin et Juillet, les sous-divisions sont presque aussi nombreuses à présenter une précipitation croissante ou décroissante. En Août, les sous-divisions présentant une croissance sont plus nombreuses, contrairement à Septembre. La majorité des sous-divisions présente très peu de changement de précipitation pour les mois hors mousson. Cinq régions...

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