Long term Trend in Rainfall over Bihar during the Period 1871-2011

Abstract

An understanding of temporal variation in rainfall distribution is key requirement for the agricultural planning and management of water resources. Bihar is an eastern state in India, where agricultural activities mainly depends on the rainfall. Any change in rainfall distribution may strongly impact the agriculture of this region. Long term rainfall (1871–2011) over the state of Bihar is analyzed for temporal variation on annual and seasonal time scales. Long term changes in rainfall are studied by parametric as well as non-parametric tests like linear regression method and Mann-Kendall test. The investigation showed a long term insignificant declining trends in annual as well as winter and monsoon rainfall, where as a significant increasing trend at 95% level of confidence in pre-monsoon season. There is no significant trend in post-monsoon rainfall during the period 1871–2011. Frequency of Normal, Excess, Deficient and Scanty rainfall over Bihar during the period 1871-2011 have also been obtained by decadal analysis of rainfall. Decadal analysis indicates that the deficient years of annual as well monsoon rainfall is maximum during last decade i.e. 2001-2010. This changing rainfall trend during monsoon months can affect the agricultural activity, hydro power generation and reservoir operation in the region.