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<p>Monthly characteristics of temperature lapse rate (TLR) or gradient with latitude (TLR<sub>Lat</sub>), longitude (TLR<sub>Lon</sub>), and elevations (TLR<sub>E</sub>) in Bangladesh were analyzed using 31&#xa0;years (1980–2010) of monthly climate data from 28 stations, employing linear and multicollinearity models. TLR<sub>Lat</sub> is shallower in the summer and steeper in winter, whereas TLR<sub>Lon</sub> shows the opposite trend. Diurnal TLR<sub>R</sub> 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 (<i>e</i><sub><i>s</i></sub> LR, <i>e</i> LR, and <i>Δe</i> LR) positively correlate with TLRs, while <i>R</i> LR, <i>P</i> LR, <i>W</i><sub><i>s</i></sub> LR (excluding TLR<sub>Lon</sub>), and <i>C</i><sub><i>c</i></sub> LR correlate inversely. Summer’s TLR<sub>Lat</sub> and TLR<sub>Lon</sub> 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<sub>Lon</sub> value in summer. In winter, steep TLR<sub>Lat</sub> and shallow TLR<sub>Lon</sub> 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<sub>Lon</sub> and TLR<sub>Lat</sub> 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.</p>

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Temperature Gradient Dynamics Across Deltaic Region, Bangladesh

  • 期刊论文

  • 发表日期：

    2025年6月27日

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  • Dambaru Ballab Kattel,
  • Tandong Yao,
  • G. M. Tarekul Islam

摘要

Monthly characteristics of temperature lapse rate (TLR) or gradient with latitude (TLRLat), longitude (TLRLon), and elevations (TLRE) in Bangladesh were analyzed using 31 years (1980–2010) of monthly climate data from 28 stations, employing linear and multicollinearity models. TLRLat is shallower in the summer and steeper in winter, whereas TLRLon shows the opposite trend. Diurnal TLRR 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 (es LR, e LR, and Δe LR) positively correlate with TLRs, while R LR, P LR, Ws LR (excluding TLRLon), and Cc LR correlate inversely. Summer’s TLRLat and TLRLon 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 TLRLon value in summer. In winter, steep TLRLat and shallow TLRLon 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 TLRLon and TLRLat 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.