Analysis of Rainfall Trend along with Change-point: Study on Purulia District, West Bengal, India

Although, the rainfall and scarcity of rainfall is critically important issue for the Purulia; but the analysis of rainfall is far from the proper conclusive statement till date. In this research, an attempt has been made to analyze the annual and seasonal rainfall trends along with the change point of annual rainfall in the Purulia District for ۳۵ years (۱۹۷۹ to ۲۰۱۳) using the monthly rainfall data of seven meteorological stations. The Mann-Kendall test was used to identify the trend in rainfall data and Theil-Sen’s slope estimator was utilized to assess the magnitude of trend. Trend-free pre-whitening method was used to eliminate the influence of significant lag-۱ correlation from the series. Change in magnitude was derived in terms of percentage change over mean rainfall. The Pettitt and Lanzante test had been used in the annual rainfall series to identify the most probable change point for the series of annual rainfall. After analysis, a significant trend was found at one station in annual rainfall. The seventh, fifth and third stations were identified with the highest positive change in magnitude for the annual, pre-monsoon, monsoon and post-monsoon series respectively. The highest negative change was portrayed in the first station during the Winter phase. The most probable change point was identified at ۱۹۸۷-۱۹۸۸ for all meteorological stations. In the pre-change point phase, the highest positive change was found in the southern sections and the lowest positive change was marked in the northern portions of the study area. In contrary, completely a reversed scenario was marked in the post change point phase. Therefore, it can be concluded that the tendency of rainfall was shifted in the northern portions after the change point. The findings presented in this research can be a helpful tool for the planners to strategize local level agricultural planning of the Purulia District.