Changes in monsoon precipitation patterns over Bangladesh and its teleconnections with global climate

Abstract

Understanding changes in monsoon precipitation patterns is crucial as it determines the occurrence, intensity, and duration of floods and droughts in Bangladesh. This study investigates changes in monsoon precipitation patterns in different intensities and durations over Bangladesh and their possible teleconnection with large-scale atmospheric oscillations. The changes in different thresholds at 29 stations in Bangladesh were analyzed using the Mann–Kendall (MK) test. Pearson correlation, wavelet coherence (WTC), and multiple wavelet coherence (MWC) methods were also employed to analyze and understand the potential linkage between the large-scale atmospheric circulations and monsoon precipitation indices. The results showed a significant decreasing trend in light and moderate precipitation indices, P10, D10, P20, and D20, while an increasing trend in heavy precipitation indices such as P60, D60, P60plus, and D60plus. The Pearson correlation analysis exhibited a significant correlation between the monsoon precipitation indices and the atmospheric circulation indices. WTC analysis revealed substantial coherence in the time–frequency bands of P10-Nino3.4, D10-Nino3.4, P20-SASMI (South Asian Summer Monsoon Index), P20-EASMI (East Asian Summer Monsoon Index), D20-SASMI, and P60plus-SOI (Southern Oscillation Index) indices. MWC analysis affirmed the correlation and showed the influence of the ERA5 reanalysis parameters, i.e., temperature (T850) and geopotential height at 850 hPa (G850), mean total precipitation rate (MTPR), mean vertically integrated moisture divergence (MVIMD), and summer evaporation (SEV) on the monsoon precipitation indices. The circulation pattern changes, like increasing sea surface temperature, T850, and G850, MTPR, SEV, and decreasing MVIMD, might work as the drivers of monsoon precipitation changes in Bangladesh. The findings can be helpful to address agro-economy losses due to monsoon variability through agricultural planning, flood, landslide and water resources management.