Regionalization of extreme precipitation estimates for the Alabama rainfall atlas

The Alabama Rainfall Atlas is an internet-based server for delivery of design information on the characteristics of extreme precipitation throughout the state. Products delivered include intensity-duration-frequency (IDF) curves and 24-h design storm hyetographs based on US Soil Conservation Service (now the Natural Resources Conservation Service) methods. Three databases (daily, hourly, subhourly) upon which the server relies consist of at-site estimates of generalized extreme value distribution parameters for gauging sites throughout the state. Regionalization of those at-site estimates to develop precipitation products for a user-specified location is accomplished using a hybrid estimation method that consists of a weighted average of estimators based on gauging station proximities and record lengths. The regionalization procedure provides products on demand for any user-selected location (gauged or ungauged) and does not cause discontinuities at boundaries that would result from delineation of distinct regions. The databases are compact and user-requested products are produced and delivered nearly instantaneously. These latter issues are felt to be major ones considering the internet-based delivery method.