ABSTRACT
This chapter presents the basic rainfall analytical methods that were developed to derive the rainfall statistics for flood flow predictions, including the time distribution and mass curve methods for point rainfall analyses, the intensity–duration–frequency (IDF) curves for design storm events, and rainfall temporal distributions for stormwater numerical simulations. Hydrologic cycle is the circulation of water through atmosphere, lands, lakes, and oceans. Precipitation and evaporation are the important phenomena in the hydrologic cycle. Evaporation from ocean surfaces is the main source of moisture for precipitation. A rainfall event is often recorded by the incremental amounts in time and then analyzed to obtain mass curve and intensity–duration curve. A rainfall time distribution represents the sequential incremental rainfall amounts recorded according to clock time. For a given rainfall duration and frequency, a value read from an isohyetal map is the amount of rainfall depth at design point. For hydrologic designs, it is necessary to translate the point value into an area-averaged rainfall depth.
