Trend analysis of seasonal rainfall in southern West Bengal by Sen's innovative trend analysis

Abstract

This study is formulated to access the trend pattern and behaviour of rainfall during Winter Season (Jan – Feb), Pre-Monsoon Season (March – May), Monsoon Season (June – September) and Post Monsoon Season (October – December) by Sen’s Innovative Trend Analysis Methodology. India’s Economy is heavily dependent on agriculture. India ranks second worldwide in farm outputs. As per 2018 agriculture employed more than 50% of the Indian workforce and contributed 17-18 % to country’s GDP. It is very essential to have the knowledge of spatial and temporal distribution of rainfall for a variety of applications in Hydrology and Water Resources Management. Therefore, a study area in the southern region of West Bengal is selected and daily rainfall gridded data has been collected from Indian Meteorological Department. The daily data is sorted and arranged for every grid in each district (South 24 PGS, North 24 PGS, Purba Medinipur, Pashchim Medinipur, Jhargram, Bankura, Howrah, Hooghly, Purba Bardhaman, Pashchim Bardhaman, Birbhum, Murshidabad, Naida, Purulia) for monthly data and further arranged for seasonal data. Analysis for every grid point in each district has been carried out individually by Sen’s Innovative Trend Analysis Method showing ITA plot for each grid and calculating statistical parameters, Slope and significance test for all four meteorological seasons. Output of the analysis is thoroughly discussed for each district in chapter 5, which when summarized gives the idea that for the past century, there is significant negative trend during Winter Season and Pre-Monsoon Season and significant positive trend during Monsoon Season and Post Monsoon Season. Negative trend during Winter Season and Pre-Monsoon Season indicates that there has been a gradual decrease in overall rainfall in these seasons and may continue to have a reduction in the amount of overall rainfall in those seasons, which further may introduce to lesser water availability and Drought like situations. Also, the positive trend on the other hand shows gradual increase in rainfall during Monsoon Season and Post Monsoon Season which further indicates increase in runoff of the catchment over the past century that may lead to flooding scenarios in the Southern West Bengal Region.