The present study measures management of flash flood to avoid the devastating impacts on boro rice production at Sunamganj district. This study interacts for meteorological parameter assessment with global climate data. Three major climatic parameters (precipitation, temperature and cloud fraction) have been considered for this study. These three climatic data were analyzed using numerical software EdGCM for the period 1920 to 2020 and then downscaled by Transform software. Flash floods have been classified as general flash floods and devastating flash flood. Flash floods have been reported to be severe in March and April. A trend was evaluated for the detection of flash flooding occurrences. The study concludes that when temperature is high, a small amount of rainfall can cause a slight cloud fraction to cause flooding. Flash flooding occurs when temperature is above 76oF(24.44oC), rainfall is at least 3 mm and cloud fraction is at most 46%. Furthermore, for validation Mann-Kendall trend analysis have been done. The test result discovered increasing trend for rainfall and decreasing trend for temperature and cloud fraction. Finally, an algorithm was developed in C++ program as a flash flood precaution tool which helped to prepare strategy as well as to adapt with the flash flood.