Downscaled prediction of extreme seasonal climate over Southeast Asia using a regional climate model

An attempt is made in this study to verify the performance of the regional climate model Weather Research and Forecasting (WRF) in downscaling extreme seasonal climate over Southeast Asia. First, the model performance is tested by using the European Centre for medium-range weather forecasting (ECMWF) reanalysis (ERA) interim reanalysis data as the driving boundary conditions. The WRF model at a horizontal resolution of 27km was run for 20 years covering the period 1991 to 2012. Comparing the model simulated precipitation anomalies in the extreme years of excess and deficient precipitation with observed anomalies, we find the model to reproduce the spatial distribution of the precipitation anomalies over Southeast Asia region realistically. However, the model showed biases in simulating precipitation over mainland Southeast Asia region (MLS). Satisfied with the model performance over Southeast Asia region in downscaling seasonal precipitation using ideal boundary condition, we tried to verify if the model could improve the one month lead boreal summer seasonal forecast generated by the seasonal prediction system Scale Interaction Experiment version 2 (SINTEX-F2). The model runs were carried out to cover the boreal summer seasons from 2000 to 2013 using 1 st May initial conditions. Comparing the forecast skill of SINTEX-F2 and WRF model, we find that the dynamical downscaling of the SINTEX-F2 improves the forecast over the Southeast Asia region. It is found that the WRF model forecasts have higher skill over Indonesia region compared to mainland Southeast Asia.