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

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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 : 3rd 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 - 0.25o x 0.25o

CMAP- 2.5o x 2.5o latitude/longitude grid

GPCP- 2.5o x 2.5o 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 2006-2010.

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 2006-2010 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 2006-2010 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 2006-2010 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 2006-2010 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 2006-2010 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 2006-2010 over Nepal.

Over Nepal

Area Parameter WRF (mm/d) TRMM (mm/d)

June July August JJA June July August JJA

Box-01 Rainfall 0.17 0.35 0.66 0.39 0.32 0.09 0.19 0.20

SD 0.23 0.82 0.83 0.71 0.40 0.08 0.28 0.30

Box-02 Rainfall 0.15 2.09 2.63 1.64 2.41 4.94 4.49 3.96

SD 0.19 2.61 2.66 2.39 1.81 3.98 2.64 3.12

Box-03 Rainfall 0.22 1.48 3.12 1.62 1.22 1.33 1.93 1.50

SD 0.48 1.72 2.08 1.97 1.29 1.05 1.30 1.25

Box-04 Rainfall 2.29 5.18 5.48 4.34 3.28 7.03 6.21 5.53

SD 3.57 2.80 3.01 3.42 2.22 3.13 2.80 3.16

Box-05 Rainfall 1.11 4.08 5.58 3.62 2.55 6.00 6.27 4.97

SD 1.35 2.83 3.89 3.42 1.85 2.94 3.93 3.45

Box-06 Rainfall 5.43 13.8 17.17 12.21 5.60 10.70 9.13 8.51

SD 6.92 4.83 7.96 8.26 3.31 3.79 2.94 3.95

Box-07 Rainfall 26.99 36.71 32.14 32.00 12.75 13.36 9.59 11.89

SD 7.34 4.72 6.70 7.43 4.15 3.41 2.69 3.81

Box-08 Rainfall 14.77 13.83 13.62 14.06 2.05 1.87 2.68 2.20

SD 4.52 1.81 2.49 3.15 1.11 1.25 2.02 1.54

Box-09 Rainfall 19.13 25.73 23.66 22.88 5.44 5.75 5.58 5.59

SD 4.27 3.72 4.65 5.01 2.89 3.50 3.74 3.37

Box-10 Rainfall 8.70 19.07 14.19 14.04 11.68 12.18 10.21 11.35

SD 7.27 5.38 4.88 7.23 5.02 4.41 3.92 4.50

Box-11 Rainfall 7.68 9.68 6.60 7.99 6.28 7.58 6.69 6.86

SD 4.26 4.28 2.50 3.94 3.08 2.94 2.24 2.8

Box-12 Rainfall 4.25 11.99 8.89 8.42 4.66 9.26 7.56 7.19

SD 3.48 3.52 2.36 4.47 1.94 2.51 1.84 2.83

Table : Box-wise monthly and seasonal rainfall (JJA) for WRF model, TRMM and their Standard Deviation (SD) for the year 2006-2010.

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.

Thank You for Your Kind Attention!