Analysis of Dependability of Annual and Monsoonal Rainfall in Eastern Ganga Canal Command, India

Effect of the climate change on rainfall characteristics varies spatially and must be quantified locally for optimal natural resources management. An attempt has been made to analyse the dependability in annual and monsoonal rainfall data over Eastern Ganga Canal (EGC) command area, India, for entire century, i.e. 1901–2012. The daily gridded (0.25°×0.25°) rainfall data prepared by the India Meteorological Department (IMD), Pune, are used. Long term data series are scaled to annual and monthly level. Total 12 grids of IMD rainfall data covering entire command area were selected in this study. Analysis for dry and wet year on annual scale along with five year moving average was carried out for all the grids as well as for entire command area. The analysis revealed that the chances of occurrence of wet year are more over chances of occurrence of dry year in the entire command area by the ratio of 14:13. However, data of last one and half decade has contradictory trend with higher changes of occurrence of dry year to very minimal chances of occurrence wet year over the command area. Dependable rainfall at various probability level has been estimated by employing gamma distribution analysis over the annual and monsoonal rainfall data. It was observed that mean annual and monsoonal weighted rainfall over entire command (1,165.93 mm and 901.95 mm, respectively) is much different than the 75% dependable rainfall values (985.48 mm and 727.54 mm, respectively), which generally must be used in any planning activity.