Changes in Historical Precipitation Extremes over Bangladesh

Sania Binte Mahtab, Sabbir Mostafa Khan

Abstract: Bangladesh has a tropical monsoon climate characterized by wide seasonal variations in rainfall, high temperatures, and high humidity. The fourth report by the Intergovernmental Panel on Climate Change (IPCC) stated that Bangladesh would experience heavier monsoons and that the melting of Himalayan glaciers will cause higher river flows and severe floods. Heavy rainfall is characteristic of Bangladesh. With the exception of the relatively dry western region of Rajshahi, where the annual rainfall is about 1600 mm, most parts of the country receive at least 2300 mm of rainfall per year. Because of its location just south of the foothills of the Himalayas, the region of Sylhet in northeastern Bangladesh receives the greatest average precipitation. About 80 % of Bangladesh's rain falls during the monsoon season. Climate change is one of the biggest issues confronting humanity in the 21st century. This will give rise to changes in weather patterns, and an increase in the frequency and severity of extreme events. Climate change might shift extremes towards conditions that will stress vulnerable countries such as Bangladesh. Changes in mean temperature and precipitation values could lead to amplified responses to their extreme values. The objective of the present research includes the trend analysis of precipitation extreme indices for selected meteorological stations in Bangladesh. Precipitation data from 1961-1990 collected by Bangladesh Meteorological Department (BMD) are used in this analysis. BMD data from a total of 22 stations are considered in this research. 11 extreme indices related to precipitation are considered in the present study. The precipitation extreme indices are calculated using RClimDex, which is written in statistical software package R. The maximum 1-day precipitation (RX1day) and maximum 5-day precipitation (RX5day); simple daily intensity index (SDII); numbers of heavy (R10mm), very heavy (R20mm) and extremely heavy (R50mm) precipitation days; consecutive wet days (CWD); very wet days (R95p), extremely wet days (R99p) and annual total wet-day precipitation (PRCPTOT) have been increasing in most of the BMD stations. Only consecutive dry days (CDD) are found to be decreasing. The trends of the precipitation extreme indices indicate a higher precipitation in the future.

Keywords: precipitation extremes, precipitation, climate change