Evaluation of Climate Change Variables based on Historical Data of Bangladesh

Abstract

Bangladesh is considered as one of the most vulnerable countries to be impacted by climate change. In recent times, Bangladesh is experiencing less rainfall in rainy season, warmer dry season, dominance of warm years, abnormal seasonal variation, drought conditions during pre-monsoon and post-monsoon season which is leaving the country to be more prone to climate change effects. Analysis of extreme climatic events, indices and trends is crucial to understand the climatic change pattern of a country. Though several studies have been undertaken but to the best of my information, none of them covered trend, sub trend, extreme events and indices analysis altogether to get a complete picture of the climate change pattern of entire Bangladesh.

Therefore, extensive statistical analysis was performed using meteorological data, to explore the coherent trend and sub trend to explain their changes in the time series and identify the pattern of occurrence of extreme events as well as the extreme indices and represent them using GIS mapping. For Climate change analysis, daily average rainfall and daily average, maximum and minimum temperature data of 26 stations has been collected from Bangladesh Meteorological Department (BMD) from the year 1975 to 2019 for this study.

For this study, ITA method has been used to identify trends along with sub-trend analysis of rainfall and temperature data and the reliability of ITA method has been checked with the traditional approach like MK, mMK. Sen’s slope estimator. Standard Anomaly Index (SAI) have been used to identify frequency, severity and occurrence of extreme natural events i.e., drought and flood in Bangladesh. At last, ClimPACT2 software has been used to check homogeneity and calculate extremes of temperature and rainfall using daily observed data. Arc GIS 10.3 and R 4.0.2 software has been used for mapping and data analyzing.

The analysis shows that during the last four decades climate variables changed its pattern and trend heterogeneously. Both increasing and decreasing trend of annual rainfall was observed but majority stations showed decreasing trend. The central part of the country showed significant decreasing trend for rainfall. Northern and central part of the country showed significant increasing trend for annual average temperature. Increase in maximum temperature is more prominent than in minimum temperature. The rainfall and maximum temperature are inversely related during monsoon and dry season as rainfall follows decreasing trend (0.65mm/year) and temperature shows increasing trend (0.017oC/year).

The sub-trend analysis shows that the stations which show overall positive trend, shows decreasing sub trend for medium to high intensity rainfall. For temperature the sub trend analysis shows that lower maximum and minimum temperature is increasing which is minimizing the seasonal variation of temperature and causing a warming weather throughout the whole year.

The Standard Anomaly Index analysis shows that, the occurrence of drought and wet year is alternating in nature in almost all the stations. In the past 20 years, the country’s western region experienced more drought years while the coastal region experienced more wet years.

The overall result of extreme indices analysis suggests that, Sylhet is vulnerable to temperature rise. Where all the stations experience negative trends in rainfall indices, Barisal and Rajshahi is susceptible to significant drought condition.

This study is anticipated to aid in understanding regional climate change in the South Asian region as well as in defining appropriate policies and plans to mitigate the adverse effects of climate change in Bangladesh.