Accuracy Evaluation of Rainfall Disaggregation Methods

Hourly rainfall depths are probably the most important data input for the simulation of watershed, instream, and water quality processes such as when using the Hydrological Simulation Program FORTRAN model. However, the density of stations measuring precipitation data on an hourly basis is low, so the disaggregation of daily rainfall values or the transfer of information from nearby stations is commonly applied. This investigation evaluated the accuracy of four methods for estimating hourly precipitation depths and assessed whether or not the accuracy of the estimates was a function of the distance between stations. Hourly rainfall records from 74 gauges located within or near the Chesapeake Bay watershed were used to evaluate the biases and accuracies of procedures for disaggregating measured daily depths into hourly amounts or transferring rainfall information for nearby gauges. None of the four methods provided accurate predictions of hourly rainfall, which suggests that it is difficult to get reliable estimates of hourly rainfall intensities by disaggregating daily totals or transferring hourly values from nearby gauges. However, the transfer of daily totals is more accurate than the estimation of hourly depths.