Regional Rainfall Frequency Analysis and drought reduction in the Tombigbee River Basin

Author(s): Ramirez-Avila, J.; McAnally, W.; Tagert, M.; Ortega-Achury, S.

A regional frequency analysis was conducted for precipitation to bring more detailed information about the amount and distribution of rainfall over the Tombigbee River Basin to promote efficient water resources management in the study area. In addition, the results of the regional frequency analysis were combined with climatological drought reduction information to determine the probability that a cumulative precipitation depth needed to end a drought will be equaled or exceeded at least once in a specific season in the Tombigbee River Basin. A total of 28 precipitation gages in eastern and northeastern Mississippi and western Alabama were included in the study representing 1,352 station years of record. A regional analysis methodology was utilized, and the Tombigbee River Basin was considered a homogeneous region to increase the dataset and improve the reliability of precipitation-frequency estimates. The International Center for Integrated Water Resources (ICIWaRM) Regional Analysis of Frequency Tool (ICI-RAFT) was used to develop the regional frequency analysis. The software involves the application of the L-moments to characterize the variability, skewness and kurtosis of the data, determine heterogeneity in the region, and assist in the identification of appropriate regional probability distribution(s). Verification of results indicated that the selected frequency distributions provide reliable exceedance values for precipitation. Results also showed that spring would be the season with a more probable chance of recovery from a moderate or severe drought in the Tombigbee River Basin.

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