Simulation of Indian monsoon extreme rainfall events during the decadal period of 2000-2009 using a high resolution mesoscale model

Understanding and prediction of Indian Southwest Monsoon (ISM) Rainfall and its variability are important issues for the research community, public as well as the government. Several studies reported occurrence of extreme rainfall events on certain days considered to be major disaster events during the ISM. In this study the Weather Research and Forecasting mesoscale model developed by NCEP/NCAR, USA is used to simulate the spatial and temporal distribution of rainfall and to assess its capability to simulate the extreme rainfall events. Simulations are conducted from 1 May to 30 September, for each of the years in the decade (2000-2009) using NCEP 2.5 degree reanalysis data for initial and boundary conditions and using Grell-Devenyi convection scheme. The model daily rainfall distribution is compared with the IMD gridded rainfall data considering seven zones covering different parts of India. Qualitative results as well as statistical analyses indicate the model could bring out the normal (≤5mm/day) and moderately extreme rainfall (5-10mm/day) events reasonably well with good correlations, rmse and bias. However it could not simulate the extreme rain (10-20mm/day) events in eastern, northeastern and west coastal zones. Standardized precipitation anomaly index derived independently from model and observational rainfall indicated that model could pickup the phase and magnitude of the wet and dry periods in all zones excepting a few deviations in westcoast and eastern zones. Simulations conducted for the normal monsoon year 2003 using the Kain-Fritisch convection scheme has substantially improved the rainfall simulation over the northwest, west coast, and semi-arid southeast India indicating the model sensitivity to convection parameterization.