Variations of precipitation and runoff in the Bagmati river basin, Bihar, India

The trend analysis of precipitation for four rain gauge stations and runoff for the Hayaghat station in the Bagmati river basin is carried out in this work by adopting modified Mann-Kendall and Sen's slope methods. Primary data and secondary data are used for finding the monthly, seasonal, and annual trends at four stations. Primary data are the observed rainfall from 1981 to 2013 which are collected from IMD Pune, observed runoff data are collected from CWC Patna and secondary data are the National Center for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) reanalysis rainfall data for the period 1981-2013. The research objectives are (i) to determine rainfall and runoff trend analysis, as well as the relationship between observed rainfall data and NCEP/NCAR reanalysis secondary data for four stations and (ii) to correlate between observed rainfall data and runoff data for all four seasons. The correlation analysis of observed rainfall and NCEP/NCAR reanalysis data shows a very good correlation ranging between 0.6111 and 0.7435. It is found that the trend of rainfall is increasing in the period of monsoon and post-monsoon at all selected stations except the monsoon season in Dhenge. Correlation analysis of rainfall and runoff shows a comparatively good correlation which ranges from 0.3724 to 0.4721 for all four seasons.