1. Effect of Tibetan snow on Indian Summer monsoon rainfall using RegCM3 M. S. Shekhar (India) B. R. S. B. Basnayake (Sri Lanka) A. U. Ahmed (Bangladesh) Group-16 Workshop on Theory and use of Regional Climate Model (RegCM3)

2. Introduction  The summer monsoon of southwest Asia is the largest anomaly of general circulation  Interannual variations of summer monsoon rainfall affects agriculture, water resources and the economy of the country.  The slowly varying boundary conditions at the surface of earth provides required memory in the climate system to predict averaged monsoon circulation and rainfall.  There exist an inverse relationship between Indian summer monsoon rainfall and the extent of Eurasian snow cover in the preceding season.

3. Objectives  To simulate Indian summer monsoon circulation features and Rainfall over the Indian region using NCEP/NCAR reanalysed data in RegCM3.  To conduct sensitivity experiments by using snow depth over Tibet to study its effect on Indian summer monsoon rainfall.

4. Domain Information Central Latitude- 20 o NCentral Longitude- 80 o E 57 X 51 Points 50 o E to 105 o E5 o S to 45 o N Grid distance- 110 Km

5. Data used 10’ USGS elevation data. GLCC Landuse data. OI SST NCEP Reanalysis data-II

8. June 1994 July 1994 KUO Rainfall (mm/day) June 1994July 1994 GRELL

10. No snow 0.5 m. snow June 1994

11. No snow 0.5 m. snow July 1994

12. Conclusions The Regional Climate Model (RegCM3) is able to simulate the monsoon circulation over India reasonably well. The rainfall simulated in mm/day in Grell convection scheme is closer to the observed rainfall of the India Meteorological Department compared to the Kuo. The inverse snow-ISMR relationship is confirmed by using snow depth as the boundary condition in RegCM3. The All India rainfall is reduced by almost 20-25% in the high Tibetan snow experiment than in the control experiment.