Simulation of Monsoon Precipitation over South Asia using RegCM3

The objective of this study was to explore the capability of the regional climate model RegCM3, to predict extreme weather events in south-Asia region with particular reference to precipitation during monsoon season (July, August, September) over northern mountainous and southern plain regions of Pakistan. Different cumulus arameterization schemes in RegCM3 for prediction of convective precipitation were tested for monsoon period during the years 1998 and 2001. The model predicted results compared with the satellite pictures, CRU observational data and the surface synoptic observatories data of the Pakistan Meteorological Department (PMD). This may be mentioned here, that the year 1998 was a dry year and the starting year of a severe drought which lasted up to the year 2000. This may also be added here, that during the year 2001, the precipitation over some parts of the country exceeded the normal and some areas in the northern parts of the country observed exceptionally high rainfall rate. The results indicated that some convective parameterization schemes of RegCM3, well captured the summer monsoon precipitation over south-Asia region. However, the schemes need to be selected carefully depending upon the region of any particular focus.

Some interim findings were that the Grell scheme with both closures: Arakawa-Schubert (AS) and Fritsch-Chappell (FC) satisfactorily predicted the total monthly rainfall in the northern mountainous regions of Pakistan. However, both predicted high precipitations over southern and south-eastern plain regions. Both the modified-Kuo and Betts-Miller (BM) schemes substantially under-predicted the rainfall, although the patterns were captured adequately. The modified-Kuo scheme was more close to the observed data when compared with the performance of the BM scheme It is recommended to further test the model schemes, perhaps a further improvement in the modified-Kuo scheme would yield a scheme even better than both of the Grell closures which predicted exceptionally high precipitation over south-eastern plain regions of Pakistan and the adjoining Indian regions. In a future paper we shall be presenting more results and will try to suggest some modifications in the existing schemes to be able to better capture the summer monsoon precipitation over south-Asia.

Key words: Numerical modeling, meteorological modeling, extreme events, monsoon precipitation, RegCM3.