Md. Mizanur Rahman Simulation of Seasonal Monsoon Rainfall over the SAARC Region by Dynamical Downscaling using WRF Model SAARC Meteorological Research Centre (SMRC) Dhaka, Bangladesh

Outlines  To study the performance of WRF model for the prediction of Seasonal Monsoon Rainfall over SAARC region.  Comparison of spatial and temporal distribution of observed and simulated monsoon rainfall (JJA)  Concluding Remarks

Fig. 1 : The domain of study over the SAARC region.

Domain parameters & Model physics; Horizontal Resolution : 50 km No. of grid point along X : 100 No. of grid point along Y : 104 No. of Vertical sigma levels : 27 Iterative Time step : 240 seconds Microphysics option :WSM 3-class simple ice scheme Longwave Rad. (ra_lw_physics) : rrtm scheme Shortwave Rad. (ra_sw_physics) : Dudhia scheme Integration scheme : 3 rd order Runga-Kutta Cumulus parameterization : Grell-Devenyi ensemble scheme Surface layer parameterization : Monin-Obukhov with Carslon-Bolan viscous sub- layer option Boundary layer parameterization : Yonsei University scheme Model Run

Data and Methodology Observation data are: TRMM o x 0.25 o CMAP- 2.5 o x 2.5 o latitude/longitude grid GPCP- 2.5 o x 2.5 o latitude/longitude grid  The daily rainfall data simulated by the WRF and the observed rainfall are extracted for 92 days from 01 June through 31 August for the year  The simulated rainfall is then compared with the observed rainfall.  Standard deviation of monsoon rainfall is computed

Fig. 2: Simulated and observed rainfall during JJA, 2006 obtained from the WRF model and observations recorded by TRMM, GPCP and CMAP.

Fig. 3: Simulated and observed rainfall during JJA, 2007 obtained from the WRF model and observations recorded by TRMM, GPCP and CMAP.

Fig. 4: Simulated and observed rainfall during JJA, 2008 obtained from the WRF model and observations recorded by TRMM, GPCP and CMAP.

Fig. 5: Simulated and observed rainfall during JJA, 2009 obtained from the WRF model and observations recorded by TRMM, GPCP and CMAP.

Fig. 6: Simulated and observed rainfall during JJA, 2010 obtained from the WRF model and observations recorded by TRMM.

Fig. 7: Average rainfall of JJA for simulated by WRF model and the TRMM observations.

Over Afghanistan Over Pakistan Fig. 8: Temporal plots of daily average rainfall (mm/d) from 01 June-31 August in box- 01 for the year over Afghanistan and Pakistan.

Over India Fig. 9: Temporal plots of daily average rainfall (mm/d) from 01 June-31 August at box-04, box- 05, box-06 and box-07 for the year over India.

Fig. 10: Temporal plots of daily average rainfall (mm/d) from 01 June-31 August at box-08 and box-09 for the year over Sri Lanka and Maldives. Over Sri Lanka Over Maldives

Fig. 11: Temporal plots of daily average rainfall (mm/d) from 01 June-31 August at box-10 and box-11 for the year over Bangladesh and Bhutan. Over Bangladesh Over Bhutan

Fig. 12: Temporal plots of daily average rainfall (mm/d) from 01 June-31 August at box-12 for the year over Nepal. Over Nepal

AreaParameterWRF (mm/d)TRMM (mm/d) JuneJulyAugustJJAJuneJulyAugustJJA Box-01Rainfall SD Box-02Rainfall SD Box-03Rainfall SD Box-04Rainfall SD Box-05Rainfall SD Box-06Rainfall SD Box-07Rainfall SD Box-08Rainfall SD Box-09Rainfall SD Box-10Rainfall SD Box-11Rainfall SD Box-12Rainfall SD Table : Box- wise monthly and season al rainfall (JJA) for WRF model, TRMM and their Standar d Deviati on (SD) for the year

Concluding Remarks  Results show that in general the large scale seasonal distributions of rainfall simulated by the model are depicted fairly well as compared to the observations.  The time series of the simulated rainfall over small regions represented by different boxes over the SAARC region.  The model values are generally underestimated over Afghanistan, Pakistan and northwestern parts of India, the rainfalls are overestimated in the central parts of India, Western Ghat mountains, Nepal, Bhutan, Bangladesh, Sri Lanka and Maldives.

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