Development of 24‐Hour Rainfall Frequency Maps for Louisiana

Abstract

Maximum annual 24‐hour rainfall maps for return periods of 2, 5, 10, 25, 50, and 100 years were developed by using hourly precipitation data. Data from 92 rain gauges for the period of 1948 to 1987 were compiled and combined into 26 synthesized stations. Log‐Pearson Type 3 distribution (LPEAR3) with parameter estimation by the method of moments (MOM) was used to compute the 24‐hour rainfall quantiles. This combination was found to be the best for the Louisiana rainfall data. The new isohyetal maps were compared to the U.S. Weather Bureau Technical Paper 40 (TP‐40) maps using the performance indices of the standardized mean square error (MSE) and the standardized bias. On the average, for all of the 26 synthesized stations corresponding to six return periods, the new maps reduced the MSE by 58% and the bias by 80%, as compared to the TP‐40 maps. Application of the predicted quantiles to the Soil Conservation Service (SCS) runoff model showed that the computed runoff was equally sensitive to both parameters, rainfall input, and the curve number, of the SCS rainfall‐runoff model.