MIXED FLOOD DISTRIBUTIONS AND FLOOD HYDROCLIMATOLOGY: TROPICAL AND NON-TROPICAL WEATHER PATTERNS OF 2001-2002

One common assumption in statistical analysis of flood frequency is the homogeneity of flood causing mechanisms, particularly atmospheric mechanisms. However, it is has been noted by many authors that mixed statistical distributions exist in annual peak and partial duration flood series and are commonly created by different atmospheric circulations. Further, these authors illustrate that by taking into consideration the mixed flood distributions caused by atmospheric mechanisms, a more accurate, physically based flood frequency analysis can be obtained. The purpose of this study is to illustrate the complexity introduced by multiple flood causing weather patterns in Upper Pascagoula and Lower Tombigbee drainage basins of Mississippi. A flood hydroclimatology is constructed for 2001-2002, across three different size drainage basins, the Sowashee (51.2mi2), the Sucarnoochee (135 mi2), and the Okatibbee (342.1 mi2). The analysis indicates that the peak annual floods in the three basins were created by winter frontal storms, not the much-publicized Hurricanes Isadore and Lili. In addition, flood response to all types of storms appears to be scale independent, showing little variation based upon drainage basin area. Such information can be incorporated into existing flood frequency analysis to better characterize the flood hazard in south-central Mississippi.