The study of extreme temperature conditions in Bangladesh during 1990 to 2019

Abstract

An extreme temperature is a weather phenomenon that is distinguished by marked cooling or heating of the air, or with the invasion of very cold or hot air, over a large area within a certain period. When temperature plunges 10°C or less and continue for three or more days considered as cold wave (CW). In winter season, the sun shifted southwards and Indian sub-continent get incline solar insolation. Wind enters into the country through the Himalayan foot hills and drops the day-night temperature and makes the cold feelings. On the other hand, when temperature exceed 36 degrees Celsius and last for minimum three or more days can be considered as heat wave (HW). In the pre-monsoon, south/ south westerly wind carries a high amount of moisture over Bangladesh. The heat capacity of moisture is higher than that of dry air. Solar insolation, temperature advection and moisture incursion these three phenomena are responsible for extreme temperature (HW) conditions. Backing and Veering is also responsible for especially severe and very severe CW and HW conditions. In the present study, all categories of cold wave and heat wave days (Duration) and frequencies (spell) have been studied for the winter (December to February) and Pre-monsoon (March to May) over most of the stations (34) of Bangladesh for the period 1990-2019. The highest numbers of cold wave and heat wave days are found in Srimangal (803 nights) and Jashore (927 days) of all types of events and frequencies are found Srimangal (114) for CW and Rajshahi (127) for HW during winter and pre-monsoon season respectively. January is the highest cold month and April is the highest warm month in Bangladesh. Cold nights in Bangladesh are decreased of all divisions except Barisal. The highest 5 coldest places are Srimangal, Ishurdi, Rajshahi, Chuadanga and Dinajpur and the highest hottest places are Jashore, Chuadanga, Rajshahi, Ishurdi and Satkhira on the basis of duration. Kutubdia and Teknaf had no CW or HW; Cox’s Bazrar had no CW at all. Among 30 years, 1995 is the highest coldest year and 2009 is the lowest cold day recorded year and 2014 is the highest hottest year and 2018 is the lowest hot day recorded year. By Mann-Kendall test, the HW trend of Mymensingh station has given only significant and decreasing value. From spatial distribution, it shows coldest areas which are Srimangal and northwestern parts of Bangladesh and hottest area which are western and middle-western parts of Bangladesh.