Study on climate anomalies of Bangladesh using statistically downscaled climate projections for representative concentration pathways (RCPs) of IPCC fifth assessment report

Abstract

Bangladesh being the most vulnerable country to climate change necessitates generation of climate anomalies for the whole country due to inadequate researches on CMIP5 RCP scenarios, which are new GHGs emission trajectories over IPCC SRES scenarios. Statistical Downscaling Model for the country has been developed thus using SDSM for maximum temperature, minimum temperature, rainfall and solar radiation data of BMD and CanESM2 GCM predictors. Climate projections have been performed followed by analysis of climate anomalies, shifting of season and long term drought severity for future periods 2030s (2016-2045), 2050s (2046-2065) and 2080s (2066-2095). Both average maximum and minimum temperature has been found to be increased in future making southern part of Bangladesh hotter gradually. Indications of higher climate variability has been found from higher increase of average minimum temperature than average maximum temperature and fluctuations of seasonal rainfall variations. Changes in Indian monsoon circulation triggered by increased sea surface temperature and surface temperature is the prime cause of such inter-seasonal and inter-annual climate variability. Highest annual average maximum and minimum temperature increase are found to be 2.7⁰C in Khulna and 3.3⁰C in Satkhira respectively for 2080s under RCP8.5. Seasonal average maximum temperature increase is found higher in monsoon (4.5⁰C) and post-monsoon season (4.0⁰C) considering all scenarios. On the other hand, Bangladesh will face highest increment of average minimum temperature (5.2⁰C) in post-monsoon season. Mean annual average rainfall increase has been found 8%, 9% and 19% for 2030s, 2050s and 2080s respectively under RCP8.5, whereas maximum increase is found 11% for 2080s under RCP4.5. Pre-monsoon and monsoon average rainfall increase are found to be 10%-22% and 10%-16% respectively, whereas rainfall is found to be decreased 7%-8% in winter and 15%-17% in post-monsoon, making dry season drier. Highest average rainfall increase would be occurred on northern part of Bangladesh up to 33% in Dinajpur and on an average 24% in north-west region in 2080s considering three RCPs. Mean annual average solar radiation is found to be decreased for all RCPs except 2030s in RCP4.5 and RCP8.5. Although, change of mean annual average radiation is very less in between -0.1% to -0.4%, it can hamper future agriculture production. Season of rainfall has been found shifting towards pre-monsoon in the eastern portion of Bangladesh with relative to 1971-2000 decreasing monsoon rainfall occurrence except north-west and south-west regions of Bangladesh. Highest increase in occurrence of pre-monsoon rainfall is found to be 5%-6% in in north-eastern region, which clearly depicts that haor area of Bangladesh will be more prone to early rainfall as well as early flash floods in future period. Occurrence of severe and extreme meteorological long term drought will be increased almost all over Bangladesh in 2080s through decreasing occurrence of mild and moderate drought. Chance of increasing occurrence of severe drought is higher than extreme drought in both RCP4.5 and RCP8.5 scenarios. In most of the regions, occurrence of mild drought will be increased in 2050s and later decreased in 2080s for both RCPs. North-west region will remain drought prone in future. Occurrence of moderate, severe and extreme drought will be increased in far future up to 14%, up to 7% and up to 4% respectively considering RCP4.5 and RCP8.5. Duration of total drought occurrence will be decreased in 2050s, but will increase up to 8% throughout the country in 2080s considering both RCPs. Total duration of long term drought occurrence will be increased all over the western Bangladesh than other parts of the country with relative to 1981-2010. North-west region will face intensive severe drought spell than historical period. South west portion of Bangladesh will become prone to longer term drought with relative to 1981-2010. Total duration of drought occurrence will be decreased in eastern hill and north east regions. However, it is also clear that there is very insignificant correlation exist between overall rainfall pattern and long term drought over Bangladesh.