Validation of the WRF regional climate model over the subregions of Southeast Asia: Climatology and interannual variability

This study investigates the capability of a regional climate model in simulating the climate variability over Southeast Asia (SE Asia). The present-day climate, covering the period 1991 to 2015, was dynamically downscaled using the Weather Research and Forecasting (WRF) model with a horizontal resolution of 27 km. The initial and boundary conditions for the WRF model is provided with the European Centre for medium-range weather forecasting (ECMWF) reanalysis (ERA-Interim) data. The model reproduced the mean precipitation climatology as well as the annual cycle. Nevertheless, the model overestimated the boreal summer precipitation over the SE Asian mainland, and underestimated the boreal winter precipitation over the Indonesian region. Model biases are associated with the bias in simulating the vertically integrated moisture fluxes. At an interannual scale, the model shows good performance over the SE Asian mainland and the Philippines in all seasons except for the boreal summer. The influence of El Nino/Southern Oscillation (ENSO) on rainfall over mainland SE Asia and the Philippines during JJA is weak, and the model successfully simulated the weak relationship realistically. In contrast, model interannual variability over the Indonesia region is good only in boreal summer and autumn seasons. This is because the model successfully simulated the significant negative correlation between rainfall and ENSO. The influence of the Indian Ocean Dipole (IOD) is seen only in the boreal autumn over the Indonesian region, and the model reproduced it reasonably well. The improvement in the representation of precipitation anomaly associated with ENSO/IOD is due to reasonably accurate simulation of large-scale circulation over SE Asia.