Final Selection of the Discharge Station Records to be Included in the Hydro-Climatic Data Network (HCDN) In Reply Refer To: August 9, 1989 WGS-Mail Stop 415 SENT EDOC REPLY REQUESTED BY SEPTEMBER 1, 1989 OFFICE OF SURFACE WATER TECHNICAL MEMORANDUM NO. 89.15 Subject: PROGRAMS AND PLANS--Final Selection of the Discharge Station Records to be Included in the Hydro-Climatic Data Network (HCDN) The Office of Surface Water (OSW) expresses its thanks to the Districts for their response to Technical Memorandum No. 88.05, requesting assistance in defining a list of discharge records suitable for climatological analysis as part of the U.S. Geological Survey (USGS) Hydro-Climatic Data Network. All of the responses have been consolidated and either Jim Slack or Jurate Landwehr has talked to each District about their choices. A list of the stations suggested for each State is being transmitted separately to each District and State Office Chief and to previously designated District contacts. They should review this list and make ANY corrections, additions, and deletions which are necessary to make the list consistent with the criteria restated below. The purpose of establishing this list is to provide a single, division-wide compilation of discharge stations having periods of record for which the monthly and annual streamflow values are suitable for climatological analysis. From the comments of the 60 or so District and Regional staff members who have helped assemble this list, it was discovered that there was a much wider interpre- tation than was expected of the suggested criteria for selecting stations given in OSW Technical Memorandum 88.05. Also, several of you have raised important questions and issues which were not fully addressed or even foreseen. As a result, the present list should have a final review for conformance and national unifor- mity. There are likely some stations or periods of record on the list which should not be there. Likewise, there may be suitable stations and periods of record which are missing, and some selections need better annotation. The accuracy of this list is critical--there is great interest in using the USGS data in climate change studies throughout the hydrologic community. This list will form the basis of a report which we expect will receive worldwide circulation, for example, through our current participation in an experiment for the World Meteorological Organization. We have already received numerous requests for the list, or parts of the list, from outside the agency, both from other Federal agencies and from the academic community. However, in the interest of accuracy and to avoid favoritism in distributing USGS data, we are not honoring any of these requests until the list is finalized in a Survey report. We request that you refrain from distributing the list in whole or in part until then as well. By separate memo, we are providing our contacts in each district with further specific instructions for preparing the revised list, plus other supporting material to assist in the review. Please ensure that great care is taken to review this list bearing in mind the potential embarrassment of having included unsuitable periods of record or having missed key stations. THE RESPONSIBIL- ITY FOR A COMPLETE AND ACCURATE LIST IS AT THE DISTRICT LEVEL. There will be no higher level technical screening of the individual records which the District chooses. Below is a clarification and expansion of the selection criteria of OSW Technical Memorandum 88.05. Please remember there may be exceptions to any of these criteria. We need to document such exemptions on a station-by-station basis by means of an explanatory comment in the list. Criterion of record length: At least 20 years of suitable record. If a station has been operated for 50 years and only the first 20 years are free of defects discussed below, then only that 20 years should be selected. If, however, a shorter record is all that is available to fill a gap in geographic or climatic repre- sentation, it is acceptable. A specific example is the inclusion of short records from islands in the Pacific because that is all that is available for that geographic region. Criterion of data quality: A rating of "good" or "excellent" on nearly all of the annual daily discharge records. A few days in some years rated "poor" or "fair" because of estimated record or similar considerations would not necessarily disqualify a sta- tion, nor would a few years rated "poor" or "fair" out of many rated "good" or "excellent." Criterion of coverage: Broad geographic and diverse climatic representation across the country. We prefer to have too many stations rather than too few. It is always more desirable for the individual users to have the option of paring down the list according to whatever density or accounting criteria they choose than to be supplied with an insufficient number of stations. Thus we now consider the suggestion of one or two stations in each accounting unit or areal rectangle as, at best, a desirable mini- mum. ALL stations and periods of record which fit the other criteria should be included in the list. (We are currently expecting a network of about 1000 stations.) Criterion of natural conditions: Minimal anthropogenic effects such as diversion, augmentation, land-use changes, or regulation of the stream discharge or reduction of base flow due to extreme ground-water pumping. This is the most difficult criterion. The objective is to include a discharge station if the anthropogenic effects are not felt to mask the effects of climate variation in the monthly and annual values. a. Stations subject to regulations by dams are generally not acceptable. However, as an example, a low-head hydropower dam which has only a transient effect on high or low flows, but not on the monthly values, is acceptable. This effect should be noted. b. Stations subject to diversion or transfer for any use are generally not acceptable. However, if the diversion has existed essentially unchanged for the entire period of record, the station may be acceptable. For example, a station in, say, the Nevada desert may be subject to diversions for irrigation but the prac- tice has remained unchanged over the entire period of record. So, while the diversions exist, and do affect the actual values, the process by which they alter the record is, in a sense, unchanging and does not significantly confound the influence of climate on the record. These considerations should be noted. c. A station in a basin which has undergone a substantial change in usage, say forest to agriculture or urban, is probably not suitable even if the change was gradual. If such a station is included, such change should be noted. PLEASE NOTE: Even though it will be stressed in the report that the selected periods have been qualified so that at least the monthly averages meet our criteria, users of this data set may wish to do analyses on a shorter time step, possibly daily. Please indicate any conditions which would make the discharge records unsuitable for analysis at less than a monthly resolution. Criterion of basin size: There was a typographical error in this criterion in OSW Technical Memorandum 88.05. The range listed should have been 100 to 10,000 square miles. In practice-- given the exception granted for the "Big Five" rivers, the excep- tion granted for the Benchmark stations, and the exceptions granted to achieve the desired coverage--this criterion has little meaning and should be ignored. Inclusion of formerly suitable stations: If a station is not presently suitable because of regulation, diversion, augmentation, or because it has been discontinued but had a period of record which on its own is suitable, the suitable period should be listed. Likewise, the fact that a station might soon be discon- tinued or become regulated is not cause to exclude it. We are making no statement about the suitability of records for water year 1989 or later. The heart of this effort is to identify existing periods of record suitable for climate analysis. Ques- tions of funding to continue or re-establish any station are not germane to this study. Exclusion of constructed records: Records that are con- structed (e.g., the Four Rivers Index of the Sacramento Basin) or re-constructed (e.g., the "natural flow" for the Colorado River at Lee's Ferry) from other sites or information on diversions, aug- mentation, pumping, regulation, etc. are generally not suitable. While such records may be indicative of current conditions, we wish to avoid the question of whether the computational algorithm might disguise the effects of climate. We do not mean to exclude stations for which the effect of diversions, etc., are easily and routinely corrected. A comment to this effect should be included for these records. Explanation of Benchmark and Current Conditions stations: One impetus for this study was the desire to reconcile the differences between several lists of "indicator" stations that have been used within the Water Resources Division. These lists were described at the end of OSW Technical Memorandum 88.05. We want to clarify in the report why a Benchmark or Current Conditions station not in the final list is not suitable for climate analysis. Most reasons are straightforward. For example, Crater Lake, Oregon, is a Benchmark station but is not a discharge station. Similarly, the Sacramento River at Verona, California, is a Current Conditions station but is highly regulated. We ask you to provide any such reasons why all or part of the record at these sites should not be included in the HCDN. Reconciliation of the National Water Summary (NWS) stations: Since we began this project, one other consideration has arisen. The original compilation was provided to the Office of Long Range Planning and Assessment as a help in getting the State reports for the 1988-89 National Water Summary started. The NWS had its own objectives and criterion. Some stations which were not in our original list nor were suggested to us for inclusion in the HCDN by the District in commenting on the original list have been used for the NWS study. Please reconsider the suitability of any station that was in the NWS study but does not appear on the HCDN list. In particular, we have noted each drought index station that was used in the NWS work but was not selected by the District for the Hydro-Climatic Data Network with the notation "NWS*" in the "Last usable Water Year column". Please comment on the suit- ability of these and any other NWS stations--in particular, the flood index stations if they differ from the drought index stations--for inclusion in the HCDN list. Please return your comments, preferably by EDOC, to JRSLACK (WR and CR) or JMLANDWEHR (SR and NR) no later than September 1, 1989. An official report on the results should be available by December 1989 at which time the list will be available for distribution. Again, OSW wishes to thank those in the Districts that have par- ticipated in this project. Their efforts will help make this network an important scientific tool. Charles W. Boning Chief, Office of Surface Water WRD Distribution: A, B, S, FO, PO Copy to: Jim Slack, WRD, Menlo Park, California Jurate Landwehr, WRD, Reston, Virginia