Analysis of rainfall trend using non-parametric methods and innovative trend analysis during 1901-2020 in seven states of North East India

In this study, we analysed the variability and trends in annual as well as seasonal rainfall in the seven states of North East India for the period 1901-2020, using non-parametric tests like Mann-Kendall, trend-free pre-whitening Mann-Kendall, modified Mann-Kendall (MMK), as well as using the innovative trend analysis (ITA). The study revealed the variabilities in annual and seasonal rainfall in these seven states. In most cases, the results of all the tests were identical. However, significant differences were observed in the case of post-monsoon rainfall of Assam and Meghalaya, pre-monsoon rainfall of Arunachal Pradesh, Mizoram and Tripura, as well as in winter rainfall of Arunachal Pradesh and monsoon rainfall of Tripura. Compared to the other states of NE India and other tests, ITA detected no significant annual trend for Tripura; however, the winter season exhibited a decreasing trend. It was observed that only the MMK test could predict such changes in rainfall distribution across seasons to a certain extent at varying significance levels in comparison to the other three methods. Since these states are vulnerable to water-related disasters, this study could help policymakers arrive at valuable climatic and water resource management decisions.