Spatial and Temporal Variations of Precipitation in and around Bangladesh

Abstract

Radar data from the Bangladesh Meteorological Department (BMD) are employed as a preliminary analysis. This is a first research work to investigate the spatial and temporal distribution of rainfall over the country for 135 consecutive days, from 16 April to 30 August 2000. Radar data are sampled in 10 km grid boxes to obtain daily rainfall over the country. Rain gauge data at 33 locations are utilized to check the radar results. The distributions of rainfall obtained by both the radar and the rain gauges are similarin pattern, but the time of the maximum rainfall determined by the radar is a few hours earlier than that determined by the rain gauges. The distribution of rainfall over the whole radar domain suggests that 21 to 09 local standard time (LST) is the most likely time for rainfall to occur in Bangladesh, while 06 LST is the most likely time for maximum rainfall to occur over the entire country. It is mentioned that no data are available between 03-06 LST. The occurrence of 21 to 09 LST rainfall is possibly linked to the local effects such as complex terrain and sea and land breeze circulations. The morning maximum rainfall at 06 LST in Bangladesh is different from that of the Indian subcontinent or of the mountain area where, generally, maximum rainfall occurs in the afternoon. The northern border of Bangladesh, close to the Shillong hill of India, is the region with the highest rainfall, while the second highest volume of rainfall occurs on the eastern border. In order to observe the characteristics of large-scale cloud activity, analyses of the Japanese GMS-5 hourly infrared data, within a larger domain of 80°-100°E and 10-30°N were conducted. The cloud activities in and around Bangladesh were obtained in 10 by 10 grid boxes. The northwestern part of Bangladesh was largely affected by pre-monsoon clouds, while the whole country was affected by the peak monsoon activities.