Abstract:
Southwestern Bangladesh is increasingly becoming vulnerable to droughts and heat waves, which pose significant risks to water security, agricultural productivity, and human health. This study develops drought and heat wave scenarios for the region from 2015 to 2100 using Coupled Model Intercomparison Project Phase 6 (CMIP6) climate projections under SSP126 (sustainability pathway) and SSP585 (fossil fueled development) scenarios. Taylor diagrams and statistical metrics, including root mean square error (RMSE), Pearson correlation coefficient, and standard deviation, were computed using Python programming language to evaluate CMIP6 models against observed data from 1995–2014 at 14 Bangladesh Meteorological Department (BMD) stations. The best-performing models selected were GFDL-CM4 for rainfall, CMCC-ESM2 for temperature, and EC-Earth3 for humidity. Then Quantile Delta Mapping (QDM) was applied to correct biases in the model outputs, aligning the model data with the observed data from the BMD stations. Droughts were assessed using the Standardized Precipitation Index (SPI3) and Standardized Precipitation Evapotranspiration Index (SPEI3), while heat waves were evaluated based on daily maximum temperatures (≥36°C for 3 consecutive days). Additionally, Heat Index (HI) was calculated for heat stress evaluation (HI > 40°C).
The results reveal notable differences between SSP126 and SSP585 scenario. Rainfall shows no significant trend under either scenario. However, temperature increases substantially with SSP126 projecting +1.37°C warming by 2100 and SSP585 showing +2.94°C. The SPI3 drought index indicates no significant trend with near normal condition under both scenarios. However, SPEI3, which incorporates temperature-driven evapotranspiration, shows pronounced divergence: SSP126 maintains relatively moderate drought conditions (2.61 drought months/year by 2100), while SSP585 progresses to severe drought (6.34 months/year by 2100).
Heat wave frequency exhibits substantial difference of around 30 days between two scenarios. Under SSP126, heat wave days show modest increases averaging 20-25 days annually throughout the century. However, under SSP585, heat waves escalate dramatically from similar levels to SSP126 until 2050, then increase to 50-58 days annually by 2100, with central and southern coastal areas bearing the highest burden reaching 35-40 days annually. March emerges as the dominant heatwave month under both SSP scenarios, representing a significant temporal shift where the peak heatwave period advances from the historical April-May months to an earlier March onset. Heat Index analysis reveals that SSP126 maintains annual average values below the 40°C heat stress threshold, while SSP585 exceeds the threshold. Moreover, heat stress threshold is exceeded 8.02 months/year under SSP585 scenario compared to 5.49 months/year under the baseline condition.
Under SSP585 scenario, southwestern Bangladesh could face catastrophic drought and heatwave conditions. Findings provide scientific evidence for climate change adaptation planning, emphasizing urgent needs for improved water management, heat protection infrastructure, agricultural resilience, and health system.