Objective: The monsoon year 2009 is a severe drought with 21.8% deficit rainfall from the long period average according to India Meteorological Department (IMD) over India since the past decade and 2010 is a normal monsoon year. Therefore, the verification skill of the VARSHA model has been computed for one normal monsoon and one drought year.
Method:The statistical parameters like mean error, root mean square error and correlation coefficient has been computed at every model grid point and verified against the rainfall observations from India Meteorological Department and Tropical Rainfall Measuring Mission (TRMM). The analysis is also extended to dichotomous forecasts, i.e. yes/no forecasts, by using contingency tables. The four regions namely, South peninsula, Central India, North-East and North-West regions of Indian land mass have been considered for the verification analysis.Result: India receives a major portion of its annual rainfall during the summer monsoon season (June to September) and thus accurate prediction of summer monsoon rainfall is very crucial. Rainfall is a discrete parameter which shows large variations spatially as well as temporally. VARSHA, a hydrostatic global circulation model, developed at Flosolver unit, National Aerospace Laboratories (NAL), Bangalore, is used to predict summer monsoon rainfall from the year 2005 onwards. Forecast verification serves to assess the state of the art of forecasting. Therefore, verification of the model forecast is an important task for any numerical weather prediction centre. In this study, an attempt has been made to examine the skill of VARSHA model in predicting the rainfall during summer monsoon period of 2009 and 2010.
Conclusion:The results show that model forecasts are useful at medium range and the performance of VARSHA is better in 2010 compared to 2009. The statistical skill scores show high predictability for light rain events with a decreasing tendency with an increase in intensity.