Prospect of application of extended range forecast in water resource management: a case study over the Mahanadi River basin

The present study is focused to see the performance of real-time extended range forecast (2-3 week forecast) of monsoon during the 2011 flood event over the eastern state of Odisha in India. The usefulness of such forecast in the management of reservoir flow in a way to reduce the risk of flood conditions is also discussed. This case study is carried out over the Mahanadi River basin situated in eastern region of India, which witnessed severe flood conditions during the late August and early part of September 2011 due to abnormally high rainfall over the Mahanadi River basins leading to simultaneous release of huge volume of water from the Hirakud reservoir. The forecasts are prepared based on the Bi-model average (BMA) of two coupled model outputs viz., the European Centre for Medium-Range Weather Forecasting (ECMWF) monthly forecast model and the National Centre for Environmental Prediction (NCEP) Climate Forecast System (CFS) coupled model. The synoptic analysis of the observed rainfall patterns demonstrated that the heavy rainfall is associated with active monsoon circulation during late August and early September, 2011 with the presence of low-pressure systems and anomalous cyclonic circulations at lower level. The extended range BMA forecast based on the initial condition of 25 August, 2011 valid for week 1 (days 5-11) and week 2 (days 12-18) indicate strong monsoon conditions associated with heavy rainfall over the Mahanadi River basins during the period from 29 August to 11 September 2011. With respect to individual model, the ECMWF model is better compared to NCEP CFS in capturing this rainfall episode, although it is much less compared to observed rainfall departure during the period. A mechanism to use such climate forecast along with the use of latest climatological information in the decision making process will be very useful for effective management of reservoir operation particularly during this difficult period.