Thermal bioclimatic transformations in the coastal regions of Ganges delta: insights from CMIP6 multi-model ensemble.

Thermal Bioclimatic Indicators (TBIs) are essential for understanding climate variability and its impacts on ecosystems and human societies, which are commonly utilized to assess the effects of climate change on biodiversity, pollution, agricultural production, and human thermal comfort. The Ganges Delta, one of the world's most biologically diverse coastal regions, is highly vulnerable to climate change. This study employs a multi-model ensemble of sixteen CMIP6 global climate models to assess future changes in eleven TBIs under SSP1-2.6, SSP2-4.5, and SSP5-8.5 scenarios. Projections indicate a significant increase in annual temperatures by 0.71-1.91 °C (SSP1-2.6), 0.77-2.80 °C (SSP2-4.5), and 1.03-4.65 °C (SSP5-8.5) by 2100. The diurnal temperature range is projected to decline by up to 0.87 °C, while isothermality may decrease by 3.30-12.09%, indicating shifts in thermal stability. Additionally, the driest months are expected to experience more pronounced warming than the wettest months. These thermal transformations pose significant threats to biodiversity, agriculture, and coastal communities, increasing risks of habitat loss, declining agricultural productivity, and altered hydrological patterns. Adaptive strategies such as tidal river management, mangrove afforestation, and conservation initiatives are essential to enhance resilience. The findings underscore the urgency of climate-responsive policies to mitigate risks and ensure the long-term sustainability of this ecologically and economically vital region.