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Statistical trend characteristics of rainfall over Kerala, India evaluated through analysing modern era retrospective analysis for research and applications (MERRA-2) reanalysis data
Author(s)
Modon Valappil, Ninu Krishnan
de Oliveira Júnior, José Francisco
Mendes, David
Hamza, Vijith
Date Issued
December 1, 2025
Type
Article
Abstract
Statistical trends of rainfall (annual and seasonal rainfalls) in Kerala, India were characterised using the 44-years (1980–2023) data of Modern-Era Retrospective Analysis for Research and Applications (MERRA) version 2. Monthly rainfall data were collected from the selected fifty locations which represent the state as a whole, and the collected data were then categorised into annual as well as seasonal (winter, summer, monsoon and post-monsoon) datasets based on the classification proposed by Indian Meteorological Organisation (IMD). Lag-1 autocorrelation, modified Mann Kendall (mMK), Pettitt test and Theil-Sen’s slope methods were used to determine the statistical characteristics of rainfalls in Kerala. Mean rainfalls were 3124 mm, 66 mm, 527 mm, 1667 mm and 862 mm, respectively, for annual, winter, summer, monsoon and post-monsoon periods. mMK based statistical trend analysis revealed an overall decreasing trend characteristics in annual (-0.54 mm.y−1), monsoon (-1.20 mm.y−1), and post-monsoon (-0.93 mm.y−1) seasons whereas winter and summer rainfalls showed an increasing trend (0.67 mm.y−1 and 3.40 mm.y−1, respectively) for the state as a single unit. Pettitt test indicated four dominant periods of change in rainfall characteristics in the study area that spanned over the decades of 1980, 1990, 2000 and 2010, in which major changes in annual and seasonal rainfalls were occurred during 1990’s, 2000’s and 2010’s. Theil-Sen’s slope-based estimation of rate of change in rainfall showed an average variation of -4.33 mm.y−1, 0.17 mm.y−1, 6.27 mm.y−1, -6.54 mm.y−1 and − 3.28 mm.y−1 for annual, winter, summer, monsoon and post-monsoon seasons, respectively. Though the winter and summer rainfalls showed an increase in its rate during the period of analysis, annual rainfall showed an overall reduction in the amount of rainfall received in the state. The study ultimately demonstrated a prevailing trend of declining rainfall within the state. The analysis highlighted the spatial variability in the rate of change of rainfall across the study area, which possesses unique climatic features. This variability underscores the influence of climate change on the region’s rainfall patterns, necessitating a comprehensive examination to develop strategies aimed at mitigating the adverse effects of climate change on agricultural and water resources.
Citation
Bulletin of Atmospheric Science and Technology, 6(1), 2025