Abstract:
Tropical Rainfall Measuring Mission (TRMM) was designed to provide measurements
of the precipitation over the tropical regions since December 1997. Recently new
version TRMM 3B42 V7 product is released which is much updated than earlier
versions. To study the extreme rainfall events and possibility to use of TRMM data in
Bangladesh, TRMM 3B42 V6 and V7 three hourly data of spatial resolution of 0.25
degree by 0.25 degree and three hourly rain gauge data of 34 stations of Bangladesh
Meteorological Department (BMD) are used. Seasonal, daily, monthly and yearly
variation of rainfall, yearly variation of different threshold and extreme rainfall events
and their spatial distribution are studied during 1998-2010. It is found that rain gauge
data are highly correlated with TRMM V7 than that of V6 data. The seasonal correlation
coefficients between BMD and V7 (V6) are 0.97 (0.88), 0.94 (0.72), 0.96 (0.88) and
0.94 (0.90) for pre-monsoon, monsoon, post-monsoon and winter, respectively. The
daily, monthly and yearly correlation coefficients between BMD and V7 (V6) are 0.96
(0.90), 0.95 (0.80) and 0.94 (0.75), respectively. Spatial pattern of rainfall of TRMM V7
was similar with that of rain gauge. The annual rainfall showed increasing gradients
from western to eastern part of the country. The overall performance of TRMM was
better for the plain land region than hilly and coastal regions. Very heavy rainfall (VHR
> 88 mm in 24 hour), heavy rainfall (88 ≥ HR ≥ 43.5 mm in 24 hour) and moderately
heavy rainfall (43.5 > MHR ≥ 22.5 mm in 24 hour) events are dominated in coastal,
southeastern and northeastern part of the country. BMD, TRMM V7 and V6 were
observed 4.10, 4.80 and 3.67 VHR events per year, respectively. The average highest
(12 events) and lowest (01 event) VHR events are found in Teknaf and Rajshahi,
respectively. TRMM V7 detects rainfall events greater than 10 mm in 24 hours more
precisely than the rainfall events less than 10 mm in 24 hours. On the other hand,
TRMM V6 detects rainfall events less than 10 mm in 24 hours more precisely. The
spatial distribution of different threshold rainfall events measured by TRMM V7 is very
much similar to rain gauge. In the case of extreme high (≥ 90th percentile) rainfall
events, it found that the performance of TRMM V7 is better than TRMM V6. On the
other hand, in the case of extreme low (≤ 10th percentile) rainfall events the
performance of TRMM V6 is better than TRMM V7. The root mean square error
(RMSE) for EHR events is lower between rain gauge and TRMM V7 than that of rain gauge
and TRMM V6. On the other hand, RMSE for ELR events is lower between rain gauge and
TRMM V6. Diurnal variation of rainfall showed two peaks at 03-06 LST and 15 LST.
