Updating the Hydro-Climatic Data Network (HCDN)
To: "A - Division Chief and Staff",
"B - Branch Chiefs and Offices",
"FO - State, District, Subdistrict and other Field Offices",
"PO - Project Offices"
cc: "CD - All Data Chiefs",
" , Computer Policy Advisory Committee, Reston, VA ",
" , WRD Archive File, Reston, VA ",
"Annette L Ledford, Clerk Typist, Reston, VA "
From: "Thomas H Yorke Jr., Chief, OSW, Reston, VA "
Subject: OSW Technical Memorandum No. 97.05
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Date: Tue, 08 Jul 1997 09:58:35 -0400
Sender: "Annette L Ledford, Clerk Typist, Reston, VA "
In Reply Refer To: July 3, 1997
Mail Stop 415
Office of Surface Water Technical Memorandum No. 97.05
Subject: Updating the Hydro-Climatic Data Network (HCDN)
The Hydro-Climatic Data Network (Water-Resources Investigations Report
93-4076) has been one of our most popular data products; it is
consistently in the 20 favorites on the wwwrvares server and has been
cited in papers in refereed journals as diverse as Freshwater Biology and
Journal of Water Resources Planning and Management. This collection of
73,231 water years of streamflow data measured at 1659 sites throughout
the United States and its territories has been of great value to those
interested in the long-term and regional variations of streamflow. The
purpose of the HCDN "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."
(Office of Surface Water (OSW) Technical Memorandum No. 89.15) The
current HCDN dataset, sometimes known as HCDN92, contains periods of
record from water year 1874 through water year 1988.
While all of our data are valuable, the HCDN has special scientific
interest as an organized, documented, and quality-assured collection of
streamflow records representing national conditions. Furthermore the
publication of this dataset on CD-ROM allows others, such as university
professors, to mount the data on their own local servers for access by
students in their hydrology classes. We feel the special effort - above
and beyond putting all of our streamflow data on the H2O server - is
warranted to keep this excellent product in the hydrologic community's
This memorandum is a request for each District to assist in updating the
records that qualify for inclusion in the HCDN. Briefly, the criteria
(first defined in OSW Memorandum No. 88.05) are that each water year of
discharge which meets the following four criteria should be included in
1. Long records: n>=20; preferably, n>=50, but the 20-year threshold
was chosen to allow the inclusion of the benchmark stations.
2. Good quality data; this pertains to the quality of the stage record,
the discharge measurements, and the stage-discharge relation.
3. Broad geographic and diverse climatologic representation across the
4. Minimal anthropogenic effects in basin, including minimal regulation
of the stream discharge or reduction of base flow due to extreme
(The fifth criteria stated in OSW 88.05 of the basin size being within a
certain range was dropped in OSW 89.15 as irrelevant, given all the
exceptions to it.) A detailed discussion of the criteria was given in OSW
89.15, the relevant portion of which is attached as an Appendix.
We are requesting that each District:
1. Review the list of acceptable record at HCDN stations they operate
(this will be sent electronically to the District Data Chief unless
the District Chief designates someone else) and report the results
of the review to Robin Sevin (email@example.com) by August 15, 1997.
Your review will determine
a. what part of the discharge record from water year 1989 through
water year 1996 at stations already in the HCDN and in operation
at the end of water year 1988 qualify for adding to the HCDN and
b. what record at stations not already in the HCDN should be added;
i.e., are there stations that didn't have 20 years of record in
1988 but otherwise qualified and that now have 20 or more years
of record which qualifies for inclusion?
2. Assure that all of the discharge data to be added to the new HCDN
(to be known as HCDN97) are available from the national web server
by September 2, 1997. The update software is available from the
Illinois District as announced in a recent email from Verne Schneider
to the field.
We plan to retrieve the new data from the H2O server in early September
and have new copies of the CD-ROM available by December 1997. Your
cooperation is supporting the HCDN and helping to make the data available
by CD-ROM are appreciated. Your efforts will further the use of our
streamflow data as an invaluable scientific tool.
(from OSW 89.15)
The accuracy of this list [the HCDN] is critical--there is great interest
in using the USGS data in climate change studies throughout the
hydrologic community. 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
RESPONSIBILITY 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 No. 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 representation, 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 station, 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 minimum. ALL stations and periods of record which fit
the other criteria should be included in the list.
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
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 practice 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
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.
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 discontinued or become regulated is not cause to
exclude it. We are making no statement about the suitability of records
for water year 1997 or later. The heart of this effort is to identify
existing periods of record suitable for climate analysis.
Exclusion of constructed records: Records that are constructed (e.g., the
Four Rivers Index of the Sacramento Basin) or reconstructed (e.g., the
"natural flow" for the Colorado River at Lee's Ferry) from other sites or
information on diversions, augmentation, 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
Thomas H. Yorke
Chief, Office of Surface Water
WRD Distribution: A, B, FO, PO