Study of extreme rainfall in Bangladesh using tropical rainfall measuring mission data

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.