A simple method for estimating convective rain volume over an area

Abstract

Previous authors have reported significant correlations between the horizontal extent of convective showers or storms and the volume of rain they produce. This paper employs that idea to develop a simplified method for estimating convective rainfall by considering only the horizontal extent and duration of the precipitation. The present analysis is based on rain gage and radar data from an area in western North Dakota. A synoptic adjustment is applied to the radar rain volume estimates. A quantity called the integrated rainfall coverage can be calculated from either gage or radar data and is found to be well correlated with the rain volumes. The maximum echo area during any one scan in one hour seems to be the hourly radar measurement best correlated with the rain volumes. This limited study suggests that the accuracy of the simplified method approaches that of methods using radar reflectivity data and may have operational value in some special situations. Many authors have shown that variations in latitude andin geographical, orographical, and synoptic conditions result in differences in radar estimated rainfall [e.g., Byers, 1948; Stout and Mueller, 1968; Estoque and Fernandez-Partagas, 1974]. In addition, there are complicating effects due to microwave attenuation, evaporation of the raindrops, vertical air motions, particle shape and fall speed variations, and advection of the rain while falling from the radar's sampling volume to the ground. The combined effects may limit the accuracy of radar estimates of areal rainfall to not better than 50% [Atlas and Chmeta, 1957; Hildebrand et at., 1979]. Nevertheless, radar can map precipitation much more completely in space and time than can any feasible network of rain gages on the surface. This capability is so valuable that experimenters in atmospheric physics, weather modification, and hydrology are • Now with the Research and Development Branch of the Office of Atmospheric Resources Research, U.S. Bureau of Reclamation, Denver, Colorado 80225.

Toward the Use of Integral Radar Volume Descriptors for Quantitative Areal Precipitation Estimation: Results from Pseudoradar Observations

“…They found that the total rainfall produced by individual storms can also be estimated simply by considering only the horizontal extent and the duration of radar-observed precipitation. Doneaud et al (1981), however, did not present a convincing explanation for the high correlations found. Later, Atlas et al (1990) recovered their approach and presented a unified theory for both the estimation of the total rainfall of an individual storm and for the average instantaneous rain rate from a multiplicity of such storms.…”

“…where P(R) denotes the value of the probability density function (pdf) at the rain rate R. The approaches of Doneaud et al (1981) and Atlas et al (1990) obviously assume that S(t) is constant for a given threshold t, that is, the theory relies on the existence of a well-behaved pdf of the rain rate either of a single storm during its…”

“…This idea is not new; Doneaud et al (1981) investigated a technique for estimating the total rain volume of precipitation events from radar data without invoking a Z-R relationship. They found that the total rainfall produced by individual storms can also be estimated simply by considering only the horizontal extent and the duration of radar-observed precipitation.…”

Stochastic modelling of rainfall from satellite data

“…Such a relationship, often seen in rainfall observations (Doneaud et al, 1981;Kedem and Pavlopoulos, 1991), is not explicitly defined within the TAM-SIM model. It can therefore be used as a further test of the ability of TAMSIM to reproduce the observed rainfall spatial structure (Onibon et al, 2004).…”

Precipitation production in three Alberta Thunderstorms

“…Since the time when digital radar data of high accuracy have become readily available -roughly 1975 -great attention has been devoted to new techniques such as Doppler and depolarization measurements but very little work has been carried out on integrated storm properties. Exceptions are certain studies motivated by the needs of hydrology, of which the research of Doneaud et al (1981) is a good example, and work by Rogers et al (1983) on the sizes and internal structure of individual rainshowers. Although these studies are related to the question of precipitation development, they do not face the question directly.…”