Spatiotemporal changes in six precipitation and five temperature extreme indices of Bangladesh and their linkage with nine ocean-atmospheric oscillation indices have been evaluated in this study to provide necessary information for adaptation planning and development of early warning systems. Daily maximum and minimum temperatures and precipitation for the period 1980–2017 recorded at 20 stations, homogeneously distributed over the country, were employed for this purpose. Modified Mann-Kendall (MMK) test was used to evaluate trends in weather extremes, and detrended fluctuation analysis (DFA) was employed to anticipate the possible continuation of existing trends in the future. The cross-wavelet transform (CWT) was used to evaluate the linkage of weather extremes with oscillation indices in the time-frequency domain. The results indicate an increase in hot extremes and a decrease in cool indices in Bangladesh. An increase in the continuous dry day (CDD) and one-day maximum precipitation (RX1day) was also observed, indicating gradual drying and more susceptibility to flash floods at the same time. DFA revealed the possible continuation of existing trends in temperature and precipitation indices. Almost all the climatic extreme indices of Bangladesh were found to follow periodic cycles with different frequencies. The hot extremes were significantly associated with five out of nine oscillation indices, including Atlantic Multidecadal Oscillation (AMO), Arctic Oscillation (AO), East Asian Summer Monsoon Index (EASMI), Sunspot, and South Asian Summer Monsoon Index (SASMI), while cool indices were linked with AMO only. Among the precipitation indices, only CDD was positively related to AO, El Niño Southern Oscillation (ENSO), and Southern Oscillation Index (SOI) and negatively associated with the Pacific Decadal Oscillation (PDO). Analysis of circulation patterns using reanalysis datasets explored that elevated summer geopotential height, no visible anticyclonic center, reduced high cloud cover, and enhanced low cloud covers contributed to increasing hot extremes in Bangladesh.

本研究评估了孟加拉国六个降水和五个极端温度指数的时空变化及其与九个海洋-大气振荡指数的联系，为适应规划和预警系统的发展提供必要的信息。为此，采用了 1980-2017 年期间在全国均匀分布的 20 个站点记录的每日最高和最低温度和降水量。使用修正的曼肯德尔 (MMK) 测试来评估极端天气的趋势，并使用去趋势波动分析 (DFA) 来预测未来现有趋势的可能延续。交叉小波变换 (CWT) 用于评估极端天气与时频域中振荡指数的联系。结果表明孟加拉国的极端炎热天气增加，凉爽指数下降。还观察到连续干旱日 (CDD) 和一天最大降水量 (RX1day) 的增加，表明同时逐渐干燥和更容易发生山洪暴发。DFA 揭示了温度和降水指数的现有趋势可能延续。发现孟加拉国几乎所有的气候极端指数都遵循不同频率的周期性循环。极端高温与九个振荡指数中的五个显着相关，包括大西洋多年代际振荡（AMO）、北极涛动（AO）、东亚夏季风指数（EASMI）、太阳黑子和南亚夏季风指数（SASMI），而酷指数仅与 AMO 相关联。在降水指数中，只有 CDD 与 AO、厄尔尼诺南方涛动 (ENSO) 和南方涛动指数 (SOI) 呈正相关，而与太平洋年代际涛动 (PDO) 呈负相关。使用再分析数据集对环流模式进行的分析探讨了夏季位势高度升高、没有可见的反气旋中心、高云量减少和低云量增加导致孟加拉国极端炎热天气增加。