Temperature Gradient Dynamics Across Deltaic Region, Bangladesh

Monthly characteristics of temperature lapse rate (TLR) or gradient with latitude (TLR_Lat), longitude (TLR_Lon), and elevations (TLR_E) in Bangladesh were analyzed using 31 years (1980–2010) of monthly climate data from 28 stations, employing linear and multicollinearity models. TLR_Lat is shallower in the summer and steeper in winter, whereas TLR_Lon shows the opposite trend. Diurnal TLR_R monthly variations peak during the pre-monsoon season and are at their lowest during the monsoon months, aligning with synoptic weather patterns and variations in moisture, rainfall, cloud cover, pressure, and wind speed. Moisture-related variables (e_s LR, e LR, and Δe LR) positively correlate with TLRs, while R LR, P LR, W_s LR (excluding TLR_Lon), and C_c LR correlate inversely. Summer’s TLR_Lat and TLR_Lon changes are driven by the southwest monsoon, causing increased rainfall and cloud cover in the southern and eastern regions. The effects of orographic rainfall further steepen the TLR_Lon value in summer. In winter, steep TLR_Lat and shallow TLR_Lon are associated with cold, dry, westerly winds, reduced rainfall, and clear skies in the northern parts. Pre-monsoon months’ TLRs exhibit steep gradients, especially in longitude, attributed to disturbances, high humidity, and frequent thunderstorms in the northeast. Post-monsoon TLR_Lon and TLR_Lat are less pronounced than pre-monsoon due to decreased rainfall and reduced thermal forcing. Diurnal patterns exhibit shallower TLRs with latitude and elevation during the day, attributed to high humidity, cloud cover, and weak adiabatic mixing. The largest diurnal range occurs during the pre-monsoon months, influenced by high sensible heat flux, radiative cooling, and frequent thunderstorms, with the smallest range occurring in summer due to elevated moisture levels, monsoon rains, high latent heat flux, and dense cloud cover. These results offer valuable insights into thermal dynamics, in addition to hydroclimatic processes and their relationship to local and regional climate and topography for variation, contributing to future hydroclimatic modeling in this region.