Analysis of the trend of dry spells and how ocean factors affect their patterns during the summer monsoon in Bangladesh using the Mann-Kendall and frontier atmospheric general circulation model

• Short-, medium-, and long-length dry spells increased at 82.35%, 73.53%, and 50% of stations. • DMI and the summer monsoon rainfall correlation coefficient is 0.34. • In El Niño years, the dry period lasted about 17% longer than in La Niña phases. • Positive westerly wind anomalies occur across Southeast Asia and the Bay of Bengal. To assess drought risk, susceptibility to food security, and water resource utilization, it is crucial to comprehend dry spell patterns from a hydrological perspective. Some regional studies have noted an extension of dry spells on a global and regional scale, but it is still unclear how often dry spells occur during the summer monsoon season, which is dominated by rainfall. This study uses the Mann-Kendall trend test to examine the trend of dry spells during Bangladesh's summer monsoon from 1985 to 2022 to close this gap. Using the frontier atmospheric general circulation model and remote sensing methods to examine the effects of ocean elements such as Indian Ocean Dipole (IOD), sea surface temperature (SST), El Niño-southern oscillation (ENSO) conditions, and the zonal wind. Daily rainfall data for 34 weather stations were obtained from the Bangladesh Meteorological Department, while surface water occurrence and change intensity data were retrieved from the JRC Global Surface Water Mapping Layers, v1.3 (FAO, UN). The NOAA Physical Sciences Laboratory (PSL) and the Tokyo Climate Center/WMO Regional Climate Centre in RA II (Asia) provided the IOD, SST, ENSO, and zonal wind data. A notable dry spell anomaly over Bangladesh was also observed in this research, with short, medium-length, and long dry spells increasing at 82.35 %, 73.53 %, and 50 % of the weather stations, respectively. Dry spells become less frequent during El Niño but more during La Niña. The climatic variability of IOD events and SST anomalies in the eastern and western tropical Indian Ocean was also noted by this study to be connected to these anomalous events. The correlation coefficient between summer monsoon rainfall and DMI is 0.34. Throughout the study period, there were changes in the upper atmosphere's and lower troposphere's wind circulation. The study allows the prioritization of regions for drought, effective water resource management, and food scarcity preparedness.