Variability of rainy days in Bangladesh during 1950-1999

Abstract

The impact of climate change on annual rainy days has received a great deal of attention by scholars worldwide. Many studies have been conducted to illustrate that changes in annual rainy days is becoming evident on a global scale. In the present study fifty years (1950-1999) daily rainfall data of 13 meteorological stations of Bangladesh Meteorological Department (BMD) have been used. Seasonal, yearly and decadal trend of variation of rainy days are studied. The whole country is divided into four regions named: South-East (SE), South-West (SW), North- East (NE) and North-West (NW). Variation of three threshold rainy days named: Moderated Heavy, Heavy and Very Heavy are studied. During pre-monsoon period in Bangladesh all the stations show increasing trend of rainy days except Srimongal. In monsoon, all the stations show increasing trend of rainy days except Dhaka, Chittagong, Cox’s Bazar, Srimongal and Rangpur. Dhaka, Chittagong, Srimongal and Bogra stations show negative trend of rainy days during postmonsoon period and all other stations show positive trend. During winter season, all stations show positive trend. All the stations show positive trend of yearly variation of rainy days except Srimongal during 1950-1999 in Bangladesh. All the stations also show positive trend of decadal variation of rainy days except Srimongal. All the stations show increasing trend of moderate heavy rainy days except Srimongal and Comilla during 1950-1999. For heavy rainy days, all the stations show positive trend except Comilla and Satkhira during 1950-1999. For very heavy rainy days, all the stations show positive trend except Mymensing, Rangpur, Bogra and Dinajpur during 1950-1999. All the four regions of Bangladesh show positive trend of variation of rainy days during pre-monsoon and monsoon periods. Among four regions, SW and NW regions show positive trend of variation of rainy days whereas SE and NE shows negative trend during postmonsoon period. All regions show positive trend of variation of rainy days during winter period. The yearly averaged rainy days in the SE, SW, NE and NW region is 115, 101, 129 and 98 days, respectively. The 50 years averaged rainy days in the pre-monsoon, monsoon, post-monsoon and winter periods is 19, 74, 16, 04 days, respectively. All the four regions show the positive trend of yearly variation of averaged rainy days with maximum and minimum in the SW and SE regions, respectively. The yearly averaged rainy days in the wet region (120 days) is higher than that of dry region (103 days) of the country. The country averaged seasonal, yearly and decadal variation of rainy days as well as three threshold rainy days show positive trend. The yearly averaged increase of rainy days is found 0.36 days/year.