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Title: Simple analytical methods of estimating short-term rainfall
Authors: Wexler, Ruth L.
Keywords: Climatic index
Daily rainfall
Hourly rainfall
Instantaneous rainfall
Rainfall distributions
Rainfall models
Publisher: U.S. Army Engineer Topographic Laboratories.
Engineer Research and Development Center (U.S.)
Series/Report no.: ETL ; 0441.
Description: Report
Abstract: Information on short-term rainfall is of interest to agriculturists, hydrologists, geomorphologists, and construction or radar engineers. Short-term rainfall has implication for soil moisture, field operations, electro-optical sensors, and equipment design or malfunction. Military planners are especially concerned with such information because of the impact of rain on mobility and trafficability. Data for rain accumulations over short periods of time are usually not available. Routine climatic precipitation data for much of the world consist of the average monthly and/or annual total amounts of rain and the responding number of rain days. The principal objective of this study is to provide simple analytical methods for recovering the frequency distributions of any short-term rainfall. The required data are the total rainfall for a given period of time and the actual duration of the rain in days, hours, or minutes for estimating daily, hourly, or instantaneous rainfall, respectively. Average Annual hourly rainfall may be estimated at times as a function of mean annual temperature. Instantaneous rainfall is limited in this study to one-hour storms or rainy periods within storms. Two rainfall models are provided. The first, the general model, is based, mainly on a particular skew distribution that was found previously to represent rainfall under very diverse conditions. This model recovers a considerable range of information for almost any rainfall occurrence. The second, or explicit, model is specific for a given average rain rate. The latter model may be utilized for situations not covered by the general model or as an alternate method. In contrast to certain of the earlier techniques, the above models (a) depend on viable rainfall mass distribution for the situation at hand and (b) determine short-term rainfall, first with respect to the percent frequency of the total duration of the rain and with respect to real time. The results yield reasonably accurate short-term rain rates for nearly 98 percent of the rain period. Either model readily determines the percent of time the average rain rate or any selected rain rate is equalled or exceeded. Of significance is the fact that the mean daily, hourly, or instantaneous rain intensity for any duration -tends to be greatly exceeded for at least -5 percent of the time. The graphs and computer programs given not only facilitate the rapid estimation of short-term rainfall for almost any situation, but also serve to improve understanding of short-term rainfall spectra.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Technical Report

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