Identification of trends in rainfall,rainy days and 24 h maximum rainfall over subtropical Assam in Northeast India |
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| Authors: | Deepak Jhajharia Brijesh K Yadav Sunil Maske Surajit Chattopadhyay Anil K Kar |
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| Institution: | 1. Department of Agricultural Engineering, North Eastern Regional Institute of Science and Technology (Deemed University), Nirjuli, Itanagar-791109, Arunachal Pradesh, India;2. Department of Land, Air and Water Resources, University of California, Davis, CA 95616-8628, USA;3. Department of Hydrology, Indian Institute of Technology, Roorkee, Roorkee-247667, Uttarakhand, India;4. Department of Computer Application, Pailan College of Management and Technology, West Bengal University of Technology, Kolkata 700104, West Bengal, India |
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| Abstract: | Trends in rainfall, rainy days and 24 h maximum rainfall are investigated using the Mann-Kendall non-parametric test at twenty-four sites of subtropical Assam located in the northeastern region of India. The trends are statistically confirmed by both the parametric and non-parametric methods and the magnitudes of significant trends are obtained through the linear regression test. In Assam, the average monsoon rainfall (rainy days) during the monsoon months of June to September is about 1606 mm (70), which accounts for about 70% (64%) of the annual rainfall (rainy days). On monthly time scales, sixteen and seventeen sites (twenty-one sites each) witnessed decreasing trends in the total rainfall (rainy days), out of which one and three trends (seven trends each) were found to be statistically significant in June and July, respectively. On the other hand, seventeen sites witnessed increasing trends in rainfall in the month of September, but none were statistically significant. In December (February), eighteen (twenty-two) sites witnessed decreasing (increasing) trends in total rainfall, out of which five (three) trends were statistically significant. For the rainy days during the months of November to January, twenty-two or more sites witnessed decreasing trends in Assam, but for nine (November), twelve (January) and eighteen (December) sites, these trends were statistically significant. These observed changes in rainfall, although most time series are not convincing as they show predominantly no significance, along with the well-reported climatic warming in monsoon and post-monsoon seasons may have implications for human health and water resources management over bio-diversity rich Northeast India. |
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| Keywords: | Trend Mann-Kendall non-parametric test Rainfall Rainy days 24 hours maximum rainfall Assam Northeast India |
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