Five Decades of Temperature Change in Bangladesh: Trends in Mean Temperature, Day-to-Day Variability, and Abrupt Temperature Shifts, 1975-2024

Abstract Long-term warming and short-term thermal variability are distinct climate properties, yet their joint evolution in Bangladesh has received limited attention. We analyzed daily average dry-bulb temperature observations obtained from the Bangladesh Meteorological Department for 43 stations during 1975–2024; 24 long-record stations were retained after reproducible quality control and completeness screening. Day-to-day temperature variability (DTV) was defined as the absolute difference between genuinely consecutive calendar days, and station-standardized 1991–2020 anomalies were aggregated to an equal-station observational network index. Sen slopes and Mann-Kendall tests were supplemented by trend-free prewhitening, Hamed-Rao variance-corrected Mann-Kendall inference, breakpoint screening, multiplicity adjustment, geographic weighting and fixed-station-network sensitivities. Annual mean temperature increased by 0.086°C decade⁻¹ (95% CI 0.029 to 0.144; TFPW p < 0.001; Hamed-Rao p = 0.004), whereas annual mean DTV changed by -0.004°C decade⁻¹ (95% CI -0.013 to 0.007; p = 0.605 and 0.442, respectively). The primary DTV ≥ 3°C event frequency also showed no statistically detectable trend (-0.411 equivalent days yr⁻¹ decade⁻¹; TFPW p = 0.196; Hamed-Rao p = 0.101). The absence of a statistically detectable mean-DTV trend persisted after excluding three breakpoint-flagged stations, geographic reweighting and a strict fixed 3-station panel. The retained Bangladesh station network therefore warmed without a parallel long-term trend in mean consecutive-day temperature variability.