Agricultural Research Management Information System

Home
Research Summary
Search
About Us
- ARMIS
- Brochure
Contact Us
Report
User Request
Data Input
Help
- Operation Manual
  - PDF
  - Video
- Program Area & Commodity
We have reached 37600 number of research entries at this moment.

- Logout

Research Detail

Home
Research
Detail

Seasonal Variations of Temperature and Rainfall Characteristics in the Northeastern Part of Bangladesh Around Sylhet

Sayeed Ahmed Choudhury
Bangladesh Meteorological Department, Sylhet-3100, Bangladesh

Toru Terao
Faculty of Education, Kagawa University,Takamatsu, Kagawa 760-8522, Japan

Fumie Murata
Faculty of Science, Kochi University, Kochi 780-8072, Japan

Taiichi Hayashi
Disaster Prevention Research Institute, Kyoto University,Uji, Kyoto 611-0011, Japan

Abstract/ Executive Summary:

Utilizing surface and satellite observations, we showed some characteristic climatic aspects in and around Sylhet area, northeastern part of Bangladesh. The 14-year climatological rainfall in pre-monsoon and monsoon seasons was calculated from TRMM-PR surface rain data. In pre-monsoon season, rainfall amount in the upper catchment of the Meghna river in India was high. The location of rainfall maximum on the Meghalaya Plateau in pre-monsoon season shifted westward relative to the monsoon season. Analysis of year-to-year variation of rainfall amount in BMD Sylhet observatory showed that the pre-monsoon rainfall contributed the year-to-year variation of the annual rainfall in Sylhet as much as the monsoon rainfall. Rainfall within 20-99 mm/h intensity range strongly affected the total rainfall for pre-monsoon season, while it was 50-499 mm/h for monsoon season. The analysis of the maximum temperature variation indicated that the temperature variation in Sylhet was largely different from that in other part of Bangladesh, especially in the rainy seasons. This was likely to be due to the cold air mass originated from the Meghalaya Plateau associated with strong rainfall activity in pre-monsoon and monsoon seasons. Recent warming trend in daily maximum temperature was prominent in Sylhet compared with other sites.

Keywords: Seasonal variations, Temperature, Rainfall northeastern part, Sylhet

Location: Sylhet rain gauge station

Start Date: 00-01-1971

End Date: 00-12-2000

Program Area: Risk Management in Agriculture

Non-commodity: Adoption and mitigation technology

Objectives:

1. To present recent warming trend especially prominent in Sylhet by comparing averaged maximum temperature for recent 14 years, the TRMM period, with that for the normal.

Methodology:

Daily and monthly rainfall data of Sylhet rain gauge station (91.88^oE, 24.90^oN, 33.53 m ASL) of Bangladesh, during the TRMM period have been collected from the Bangladesh Meteorological Department (BMD). For the comparison, we gathered the normal rainfall amount from the web site of BMD. The normal was defined as the average for the period from 1971 to 2000 in the present paper. We compared the rainfall averaged for monsoon season from 1998 to 2011 observed by the TRMM-PR and BMD Sylhet observatory. We calculated the average rainfall intensity for the pixel that covers Sylhet observatory at 24.90^oN, 91.88^oE. The TRMM-PR estimation was 0.72 mm/h, corresponding with 2116.6 mm. The ground truth was 2550.9 mm according to the BMD observation. The same comparison was made for pre-monsoon season also. The TRMM-PR and surface observations were 1011.8 and 1066.6 mm, respectively. The TRMM rainfall estimates tend to be somewhat underestimated. Islam and Uyeda (2007) pointed out the underestimation of rainfall in TRMM-3B42 V6 data for monsoon months. The bias of TRMM-PR and other recent product should be clarified more in future. Surface rainfall data from the TRMM satellite was also utilized for the estimation of detailed spatial distribution associated with the topographical features. The TRMM platform has precipitation radar (TRMM-PR) which measures rainfall rate (mm per hour) with horizontal and vertical resolution of 5km and 250m, respectively. For the present paper, we utilized the near surface rain data which is included in TRMM-2B25, which is an estimate of rainfall rate at the ground level for each radar beam. We collected the TRMM satellite data for all valid swaths, and averaged over the all observations to get rainfall rate to obtain averaged rainfall rate for averaged period. We estimated the rainfall rate for pre-monsoon (March to May) and monsoon (June to September) periods for each pixels with 0.05 times 0.05 degree size for the area 90-94oE and 23-26oN. For the monsoon periods, each pixel catches more than 1000 original pixels with 100 rainy pixels during 14-year observations on average. For the pre-monsoon periods, they were 800 and 40, respectively.

Source of Information: J. Agrofor. Environ. 6 (2): 81-88, 2012; ISSN 1995-6983

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Analysis of year-to-year variation of rainfall amount in BMD Sylhet observatory showed that the pre-monsoon rainfall contributed the year-to-year variation of the annual rainfall in Sylhet as much as the monsoon rainfall. Rainfall within 20-99 mm/h intensity range strongly affected the total rainfall for pre-monsoon season, while it was 50-499 mm/h for monsoon season. The analysis of the maximum temperature variation indicated that the temperature variation in Sylhet was largely different from that in other part of Bangladesh, especially in the rainy seasons. This was likely to be due to the cold air mass originated from the Meghalaya Plateau associated with strong rainfall activity in pre-monsoon and monsoon seasons. Recent warming trend in daily maximum temperature was prominent in Sylhet compared with other sites.

Knowledge Management: Journal