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WWRC 90-34
Evaluation of Precipitation Network in Snowy Range Observatory

Abstract

This research studies the monthly precipitation information content in the Snowy Range Observatory. The Observatory currently consists of 20 precipitation gages with varying length of record. The study was proceeded through three phases.

Phase I - Estimation of Missing Values Due to various reasons, records of all gages involves missing values. The study was first performed to compare various methods of different complexity to estimate the missing values. Although there was no single method that is universally superior in all circumstances, a simple method of linear inverse distance method was found to be rather accurate. It was then used to fill the missing values in all precipitation gages.

Phase II - Analysis of Monthly Precipitation The time series of monthly total precipitation was first analyzed station by station. The accuracy of different methods of estimating the spatial distribution of the average precipitation were investigated. Then, the spatial structures of the monthly total precipitation were identified using variogram analysis of geostatistics. Information derived from this phase serves as the basis for precipitation network analysis in the next phase.

Phase III - Precipitation Network Analysis The objective of this phase is to examine the effect of having a reduced network, in terms of gage number, on the loss of information content. The present network containing 21 gages was used as the basis for comparison. Two reduced networks each containing 15 and 12 gages, respectively, were subjectively selected on the basis of geographical location, accessibility, and aesthetic considerations. Nonstationary Kriging technique was employed to estimate the spatial distribution of error based on different network configurations. It was found that the two reduced networks have a small increase in error, as compared with 21 stations, during the months of May - September. However, increase in error could be as high as 25%-30% during the months of October April. High error occurs on the upper third of the watershed resulting from the removal of gages from the area due to accessibility consideration.


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