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Last modified
1/26/2010 2:58:40 PM
Creation date
10/12/2006 4:18:02 AM
Metadata
Fields
Template:
Water Supply Protection
File Number
8210.470
Description
Pacific Southwest Interagency Committee
State
CO
Basin
Colorado Mainstem
Water Division
5
Date
2/1/1966
Author
Unknown
Title
Report of the Hydrology Subcommittee - Limitations in Hydrologic Data - As Applied to Studies of Water Control and Water Management - February 1966
Water Supply Pro - Doc Type
Report/Study
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<br /> <br />-16- <br /> <br />Consistency of records <br /> <br />The ideal temperature record is one that has been collected at a <br />representative site where there has been little or no change in exposure, <br />instrumentation, or procedure in observing. Very few are the ststions <br />whose records satisfy these criteria, so that in most uses the records <br />first should be tested for consistency or homogeneity. Linsley, Kohler <br />and Paulhus (1949) describe a method for so testing homogeneity. Briefly, <br />observed values of temperature at the station in question are plotted <br />against the average of values at several nearby stations, with the plotted <br />points identified according to year of observation. On such a plot, a <br />break in continuity of the regression line may indicate a marked change <br />in exposure or in some other aspect ,of the station environment. Commonly <br />the full record plots in a series of regression lines that are en echelon <br />but substantially parallel. In such a situation, the early records can <br />be adjusted to match the current rec:ord by the algebraic addition of a <br />constant or constants. Any such adjustments of a temperature record <br />should be conservative. Under-adjustment is much to be preferred to over- <br />adjustment. In general, an adjustment should be made only when justified <br />by a known change in exposure of the station, or in some other competent <br />factor. ' <br /> <br />The Weather Bureau's "Key to Meteorological Records Documentation, <br />No. 1.1, Substation Histories," published by States, summarizes informa- <br />tion on location, altitude, exposure, kind of record, and observers for <br />ClimatOlogical substations. Although not all are complete, these histo- <br />ries are very useful when testing records for consistency. <br /> <br />Use of data <br /> <br />Determining averages or normals <br /> <br />In computing "normal" or average values of air temperature, care <br />Should be taken that the measurements represent the same interval of time <br />and unchanged environmental conditions. As the standard periods for <br />temperature normals the Weather Bureau has adopted consecutive 3D-year <br />periods as follows: 1 January 1921 to 31 December 1950, 1 Janaury 1931 <br />to 31 December 1960, etc. "Average" or "long-term mean" s)Jould be used <br />for reference to any other period. <br /> <br />Correlation with hydrologic parameters <br /> <br />Correlations of monthly average temperature with other hydrologic <br />parameters can be misleading. Thus, a near-normal month that includes a <br />short period of abnormally high temperature may be much more critical than <br />a month in which all the daily temperatures are slightly or moderately <br />above average. Also, the arbitrary period of a month is not necessarily <br />the best interval for hydrologic correlations. Temperature expressed as <br />accumulated degree-days may be much easier to correlate than temperature <br />expressed as an average over successive periods of fixed duration, however <br />~ong. <br />
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