Analysis of Rainfall Trends over Assam, North East India

Abstract

The spatio-temporal variations of long-term rainfall over Assam in the North Eastern part of India were analyzed using data from twenty-six locations during the period 1981-2017. The annual, monthly, and seasonal rainfall trends are assessed by using Mann-Kendall and Sen slope tests over different sub regions. September, December, January, and February months recorded decreasing trends, while May, June, and August exhibited statistically substantial increasing trends. Similarly, annual, pre monsoon season and monsoon seasons exhibited increasing trends, but post monsoon and winter seasons recorded statistically non-significant decreasing rainfall trends. The locations of Demaji, Dibrugarh, Karimganj, and North Lakhimpur were recorded with above 2000 mm annual rainfall. On seasonal time scales, pre monsoon and monsoon rainfall over Assam witnessed increasing trends with statistically notable trends. The post monsoon and winter rainfall recorded decreasing trends, but the trends were statistically non-significant. In the monsoon season, a declining trend was recorded during the first decade (2001-2010). The southern and northeastern portion of the state received the maximum average annual rainfall when compared to the central portion of the Brahmaputra valley of Assam state. The maximum variations in rainfall have been recorded in the Karimganj (36.8%), Hailakandi (31.9%), Silchar (31.9%), and Dhuburi (26.5%) regions. Any slight variations in the rainfall trend could certainly be vulnerable as the state of Assam which comprises valley flood plains and sub-Himalayan boundaries, also supports a large chunk of human as well as ecosystem populations. In the present scenario, extreme and unprecedented rainfall events can affect agricultural activities, stream flow, the availability of food, etc., which may lead to disparities in the socio-economic conditions of the area. The results would be beneficial to policymakers in understanding the impact of changing climates and assessing the climatic vulnerability of natural and human resources.