The use of precipitation data as input for conceptual hydrologic models has enhanced the need for measurements more representative of 'true' precipitation. Precipitation input to continuous watershed models is generally some form of mean basin precipitation estimate based on point measurements. Each point measurement can have large catch deficiencies due to wind, especially for solid precipitation. A brief review is made of past results from studies concerned with these deficiencies. New curves based on current studies are presented for wind-caused gage catch deficiencies for both rain and snow. The results of using gage catch correction factors to adjust precipitation input to a conceptual hydrologic model are presented.The use of precipitation measurements as a major input for conceptual hydrologic models has enhanced the need for point and areal measurements that are more representative of 'true' precipitation. Hydrologic modeling studies indicate that one of the most important factors in successful hydrologic simulation is reliable and representative precipitation data. Raw precipitation data are often converted to some form of mean basin precipitation (MBP) estimate for use in a hydrologic model. Present hydrologic models to a large degree are limited by the accuracy of the MBP estimate. Many factors influence the estimate of MBP, including density and arrangement of the network, the particular site and gage characteristics at each location within the network, methods of areal analysis utilized, basin characteristics, storm characteristics, etc. For solid precipitation the most important of all these items, however, is the gage catch deficiency due to wind [Peck, 1972]. Many studies in the past have attempted to evaluate gage catch deficiencies in terms of the causes and magnitudes of the errors [Green and Helliweli, 1972; Warnick, 1956]. In this paper a brief review is presented of some of these past results. Recent relationships for wind-caused measurement errors for both liquid and solid precipitation are presented. Finally, the results of using precipitation correction factors based on these relationships as input for a conceptual hydrologic model and a calibrated watershed are presented. REviEw OF PREVIOUS STUDIES CONCERNED WITH GAGE CATCH DEFICIENCIES Literally hundreds of articles have been published on this subject from the mid-eighteenth century to the present. Kurtyka [1953], Israelsen [1967], and Larson [1971a] have each published comprehensive literature reviews containing a total of some 1600 references in the general field of precipitation measurements. More recently, the World Meteorological Organization [1973] has published an annotated bibliography in the same subject area.Although most studies vary with one another as far as the magnitudes of gage catch deficiencies due to wind are concerned, they all reach the same general conclusions. That is,

A technique was developed in which anomalies from precipitation‐elevation relationships were used in preparing isohyetal maps of Utah. October–April and May–September precipitation normals (averages for the 1921 to 1950 period) were computed for all available Utah precipitation records. The double‐mass analysis technique was used in the derivation of the October–April normals, and for this purpose the state was separated into eight climatic divisions. Relationships between precipitation and water equivalent of snow cover at a network of 29 stations were used in estimating normal October–April precipitation for snow courses located above 8000 feet. The May–September precipitation values for short‐term stations were adjusted to the 1921–1950 period by the ratio method. The state was divided into 20 geographic zones, and for these zones it was found that good correlations existed between precipitation and station elevation for both the October–April and May–September periods. The precipitation‐elevation relationships showed marked differences for some adjacent areas separated by high mountain ranges. From combined data for several zones, general precipitation‐elevation curves for larger areas were obtained and departures of individual station normals from these curves were plotted on a contour base map. Analysis of these anomalies showed that the departures were related to physiographic features. Normal May–September and October–April values were determined for a grid of points over the state by using the anomaly pattern and general precipitation‐elevation relationships. These values, together with the observed and adjusted normals, were used to locate the October–April and May–September isohyetals. The large variations in normal precipitation due to topography were taken into account, yet the general precipitation‐elevation relationships for small zones were retained. The accuracy of the isohyetal maps is considered comparable to that obtained by presently known methods, and the technique is less time consuming.

Recent research studies have investigated an airborne gamma radiation detection system to determine the water equivalent of snowpacks in nonmountainous areas. Snow attenuates natural gamma emissions from the soil, and the magnitude of attenuation is related to the mass of the water blanket between the soil and the detector. Gamma spectral and total counting rates are collected and recorded by an airborne system using 14 4‐ by 4‐inch sodium iodide (NaI (Tl)) crystals. These data are corrected for soil moisture, background radiation, and effects of air density. Extensive snow depth and density measurements were taken to determine ‘ground truth’ water equivalent under the flight path. Results of the first year of research indicate that gamma spectral data may be expected to give areal measurement of snow water equivalent within at least 0.2–0.5 inch over favorable terrain. The use of total count data is even more promising but requires methodology still under development for eliminating background interference.

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