358 lines
16 KiB
Text
358 lines
16 KiB
Text
This documentation describes the record format for the divisional,
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statewide, regional and national drought files on
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/pub/data/cirs/climdiv that have the filenames:
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climdiv-pdsist-vx.y.z-YYYYMMDD
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climdiv-phdist-vx.y.z-YYYYMMDD
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climdiv-pmdist-vx.y.z-YYYYMMDD
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climdiv-sp01st-vx.y.z-YYYYMMDD
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climdiv-sp02st-vx.y.z-YYYYMMDD
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climdiv-sp03st-vx.y.z-YYYYMMDD
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climdiv-sp06st-vx.y.z-YYYYMMDD
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climdiv-sp09st-vx.y.z-YYYYMMDD
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climdiv-sp12st-vx.y.z-YYYYMMDD
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climdiv-sp24st-vx.y.z-YYYYMMDD
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climdiv-zndxst-vx.y.z-YYYYMMDD
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climdiv-pdsidv-vx.y.z-YYYYMMDD
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climdiv-phdidv-vx.y.z-YYYYMMDD
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climdiv-pmdidv-vx.y.z-YYYYMMDD
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climdiv-sp01dv-vx.y.z-YYYYMMDD
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climdiv-sp02dv-vx.y.z-YYYYMMDD
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climdiv-sp03dv-vx.y.z-YYYYMMDD
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climdiv-sp06dv-vx.y.z-YYYYMMDD
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climdiv-sp09dv-vx.y.z-YYYYMMDD
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climdiv-sp12dv-vx.y.z-YYYYMMDD
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climdiv-sp24dv-vx.y.z-YYYYMMDD
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climdiv-zndxdv-vx.y.z-YYYYMMDD
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nClimDiv
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STATEWIDE-REGIONAL-NATIONAL
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DROUGHT
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MARCH 2014
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The major parameters in this file are sequential climatic divisional,
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statewide, regional and national monthly Standardized Precipitation
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Index (SPI), and Palmer Drought Indices (PDSI, PHDI, PMDI, and ZNDX).
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Period of record is 1895 through latest month available, updated monthly.
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Values from the most recent two calendar years will be updated on a monthly
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basis. Period of record updates will occur when the underlying data set
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undergoes a version change.
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METHODOLOGY:
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Divisional, statewide, regional and national values in nClimDiv were derived
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from area-weighted averages of grid-point estimates interpolated from station
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data. A nominal grid resolution of 5 km was used to ensure that all divisions
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had sufficient spatial sampling (only four small divisions had less than 100
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points) and because the impact of elevation on precipitation is minimal below
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5 km. Station data were gridded via climatologically aided interpolation to
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minimize biases from topographic and network variability.
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The Global Historical Climatology Network (GHCN) Daily dataset is the source
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of station data for nClimDiv. GHCN-Daily contains several major observing
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networks in North America, five of which are used here. The primary network
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is the National Weather Service (NWS) Cooperative Observing (COOP) program,
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which consists of stations operated by volunteers as well as by agencies such
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as the Federal Aviation Administration. To improve coverage in western states
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and along international borders, nClimDiv also includes the National
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Interagency Fire Center (NIFC) Remote Automatic Weather Station (RAWS) network,
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the USDA Snow Telemetry (SNOTEL) network, the Environment Canada (EC)
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network (south of 52<35>N), and part of Mexicos Servicio Meteorologico Nacional
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(SMN) network (north of 24<32>N). Note that nClimDiv does not incorporate
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precipitation data from RAWS because that networks tipping-bucket gauges are
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unheated, leading to suspect cold-weather data.
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All GHCN-Daily stations are routinely processed through a suite of logical,
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serial, and spatial quality assurance reviews to identify erroneous
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observations. For nClimDiv, all such data were set to missing before
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computing monthly values, which in turn were subjected to additional serial
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and spatial checks to eliminate residual outliers. Overall, the quality
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assurance reviews deemed less than 0.25% of the monthly data as being
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erroneous. Stations having at least 10 years of valid monthly data since
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1950 were used in nClimDiv.
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For temperature, bias adjustments were computed to account for historical
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changes in observation time, station location, temperature instrumentation,
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and siting conditions. Changes in observation time are only problematic for
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the COOP network whereas changes in station location and instrumentation occur
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in almost all surface networks. As in the U.S. Historical Climatology Network
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version 2.5, the method of Karl et al. (1986) was applied to remove the
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observation time bias from the COOP network, and the pairwise method of Menne
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and Williams (2009) was used to address changes in station location and
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instrumentation in all networks. Because the pairwise method also largely
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accounts for local, unrepresentative trends that arise from changes in siting
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conditions, nClimDiv contains no separate adjustment in that regard.
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For additional information on how nClimDiv is constructed, please see:
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http://journals.ametsoc.org/doi/abs/10.1175/JAMC-D-13-0248.1
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Historical drought data have been added to this file for the period 1895 to
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present. The file is updated monthly. All drought data are calibrated using
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the period 1931-1990 (cf. Karl, 1986; Journal of Climate and Applied
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Meteorology, Vol. 25, No. 1, January 1986). Drought data include:
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1. Palmer Drought Severity Index (PDSI)
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This is the monthly value (index) that is generated indicating the severity
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of a wet or dry spell. This index is based on the principles of a balance
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between moisture supply and demand. Man-made changes were not considered in
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this calculation. The index generally ranges from -6 to +6, with negative
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values denoting dry spells and positive values indicating wet spells. There
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are a few values in the magnitude of +7 or -7. PDSI values 0 to -.5 =
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normal; -0.5 to -1.0 = incipient drought; -1.0 to -2.0 = mild drought; -2.0
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to -3.0 = moderate drought; -3.0 to -4.0 = severe drought; and greater than -
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4.0 = extreme drought. Similar adjectives are attached to positive values of
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wet spells. This is a meteorological drought index used to assess the
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severity of dry or wet spells of weather.
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2. Palmer Hydrological Drought Index (PHDI)
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This is the monthly value (index) generated monthly that indicates the
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severity of a wet or dry spell. This index is based on the principles of a
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balance between moisture supply and demand. Man-made changes such as
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increased irrigation, new reservoirs, and added industrial water use were not
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included in the computation of this index. The index generally ranges from -
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6 to +6, with negative values denoting dry spells, and positive values
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indicating wet spells. There are a few values in the magnitude of +7 or -7.
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PHDI values 0 to -0.5 = normal; -0.5 to -1.0 = incipient drought; -1.0 to -
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2.0 = mild drought; -2.0 to -3.0 = moderate drought; -3.0 to -4.0 = severe
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drought; and greater than -4.0 = extreme drought. Similar adjectives are
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attached to positive values of wet spells. This is a hydrological drought
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index used to assess long-term moisture supply.
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3. Palmer "Z" Index (ZNDX)
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This is the generated monthly Z values, and they can be expressed as the
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"Moisture Anomaly Index." Each monthly Z value is a measure of the departure
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from normal of the moisture climate for that month. This index can respond
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to a month of above-normal precipitation, even during periods of drought.
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Table 1 contains expected values of the Z index and other drought parameters.
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See Historical Climatology Series 3-6 through 3-9 for a detailed description
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of the drought indices.
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4. Modified Palmer Drought Severity Index (PMDI)
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This is a modification of the Palmer Drought Severity Index. The
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modification was made by the National Weather Service Climate Analysis Center
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for operational meteorological purposes. The Palmer drought program
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calculates three intermediate parallel index values each month. Only one
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value is selected as the PDSI drought index for the month. This selection is
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made internally by the program on the basis of probabilities. If the
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probability that a drought is over is 100%, then one index is used. If the
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probability that a wet spell is over is 100%, then another index is used. If
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the probability is between 0% and 100%, the third index is assigned to the
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PDSI. The modification (PMDI) incorporates a weighted average of the wet and
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dry index terms, using the probability as the weighting factor. (Thomas R.
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Heddinghause and Paul Sabol, 1991; "A Review of the Palmer Drought Severity
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Index and Where Do We Go From Here?," Proceedings of the Seventh Conference
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on Applied Climatology, pp. 242-246, American Meteorological Society, Boston,
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MA). The PMDI and PDSI will have the same value during an established
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drought or wet spell (i.e., when the probability is 100%), but they will have
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different values during transition periods.
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5. Standardized Precipitation Index (SPxx)
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This is a transformation of the probability of observing a given amount of
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precipitation in xx months. A zero index value reflects the median of the
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distribution of precipitation, a -3 indicates a very extreme dry spell, and a
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+3 indicates a very extreme wet spell. The more the index value departs from
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zero, the drier or wetter an event lasting xx months is when compared to the
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long-term climatology of the location. The index allows for comparison of
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precipitation observations at different locations with markedly different
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climates; an index value at one location expresses the same relative departure
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from median conditions at one location as at another location. It is
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calculated for different time scales since it is possible to experience dry
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conditions over one time scale while simultaneously experiencing wet conditions
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over a different time scale.
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Table 1 Classes for Wet and Dry Periods
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Approximate
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Cumulative
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Frequency Range Range
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% PHDI Category Z
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> 96 > 4.00 Extreme wetness > 3.50
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90-95 3.00, 3.99 Severe wetness 2.50, 3.49
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73-89 1.50, 2.99 Mild to moderate 1.00, 2.49
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wetness
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28-72 -1.49, 1.49 Near normal -1.24, 0.99
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11-27 -1.50, -2.99 Mild to moderate -1.25, -1.99
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drought
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5-10 -3.00, -3.99 Severe drought -2.00, -2.74
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< 4 <-4.00 Extreme drought <-2.75
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STATE CODE TABLE:
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Range of values for the states, regions, and nation is 001-110.
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001 Alabama 030 New York
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002 Arizona 031 North Carolina
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003 Arkansas 032 North Dakota
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004 California 033 Ohio
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005 Colorado 034 Oklahoma
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006 Connecticut 035 Oregon
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007 Delaware 036 Pennsylvania
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008 Florida 037 Rhode Island
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009 Georgia 038 South Carolina
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010 Idaho 039 South Dakota
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011 Illinois 040 Tennessee
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012 Indiana 041 Texas
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013 Iowa 042 Utah
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014 Kansas 043 Vermont
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015 Kentucky 044 Virginia
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016 Louisiana 045 Washington
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017 Maine 046 West Virginia
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018 Maryland 047 Wisconsin
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019 Massachusetts 048 Wyoming
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020 Michigan 101 Northeast Region
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021 Minnesota 102 East North Central Region
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022 Mississippi 103 Central Region
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023 Missouri 104 Southeast Region
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024 Montana 105 West North Central Region
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025 Nebraska 106 South Region
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026 Nevada 107 Southwest Region
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027 New Hampshire 108 Northwest Region
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028 New Jersey 109 West Region
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029 New Mexico 110 National (contiguous 48 States)
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The following are the range of code values for the National Weather
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Service Regions, river basins, and agricultural regions:
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111 Great Plains
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115 Southern Plains and Gulf Coast
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120 US Rockies and Westward
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121 NWS Eastern Region
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122 NWS Southern Region
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123 NWS Central Region
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124 NWS Western Region
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201 Pacific Northwest Basin
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202 California River Basin
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203 Great Basin
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204 Lower Colorado River Basin
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205 Upper Colorado River Basin
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206 Rio Grande River Basin
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207 Texas Gulf Coast River Basin
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208 Arkansas-White-Red Basin
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209 Lower Mississippi River Basin
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210 Missouri River Basin
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211 Souris-Red-Rainy Basin
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212 Upper Mississippi River Basin
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213 Great Lakes Basin
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214 Tennessee River Basin
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215 Ohio River Basin
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216 South Atlantic-Gulf Basin
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217 Mid-Atlantic Basin
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218 New England Basin
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220 Mississippi River Basin & Tributaties (N. of Memphis, TN)
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250 Spring Wheat Belt (area weighted)
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255 Primary Hard Red Winter Wheat Belt (area weighted)
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256 Winter Wheat Belt (area weighted)
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260 Primary Corn and Soybean Belt (area weighted)
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261 Corn Belt (area weighted)
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262 Soybean Belt (area weighted)
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265 Cotton Belt (area weighted)
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350 Spring Wheat Belt (productivity weighted)
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356 Winter Wheat Belt(productivity weighted)
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361 Corn Belt (productivity weighted)
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362 Soybean Belt (productivity weighted)
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365 Cotton Belt (productivity weighted)
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450 Spring Wheat Belt (% productivity in the Palmer Z Index)
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456 Winter Wheat Belt (% productivity in the Palmer Z Index)
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461 Corn Belt (% productivity in the Palmer Z Index)
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462 Soybean Belt (% productivity in the Palmer Z Index)
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465 Cotton Belt (% productivity in the Palmer Z Index)
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DIVISIONAL FILE FORMAT:
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Element Record
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Name Position Element Description
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STATE-CODE 1-2 STATE-CODE as indicated in State Code Table as
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described in FILE 1. Range of values is 01-91.
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DIVISION-NUMBER 3-4 DIVISION NUMBER - Assigned by NCDC. Range of
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values 01-10.
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STATE/REGIONAL/NATIONAL FILE FORMAT:
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STATE-CODE 1-3 STATE-CODE as indicated in State Code Table above.
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Range of values is 001-110 for standard states,
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regions and national, 111-465 for special regions.
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DIVISION-NUMBER 4 DIVISION NUMBER. Value is 0 which indicates an area
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-averaged element.
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REMAINING FILE FORMAT FOR DIVISIONAL/STATE/REGIONAL/NATIONAL:
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ELEMENT CODE 5-6 05 = PDSI
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06 = PHDI
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07 = ZNDX
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08 = PMDI
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71 = 1-month Standardized Precipitation Index
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72 = 2-month Standardized Precipitation Index
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73 = 3-month Standardized Precipitation Index
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74 = 6-month Standardized Precipitation Index
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75 = 9-month Standardized Precipitation Index
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76 = 12-month Standardized Precipitation Index
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77 = 24-month Standardized Precipitation Index
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YEAR 7-10 This is the year of record. Range is 1895 to
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current year processed.
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(all data values are right justified):
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JAN-VALUE 11-17 Palmer Drought Index format (f7.2)
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Range of values -20.00 to 20.00. Decimal point
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retains a position in 7-character field.
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Missing values in the latest year are indicated
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by -99.99.
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Standardized Precipitation Index format (f7.2).
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Range of values -4.00 to 4.00. Decimal
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point retains a position in 7-character field.
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Missing values in the latest year are indicated
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by -99.99.
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FEB-VALUE 18-24
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MAR-VALUE 25-31
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APR-VALUE 32-38
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MAY-VALUE 39-45
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JUNE-VALUE 46-52
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JULY-VALUE 53-59
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AUG-VALUE 60-66
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SEPT-VALUE 67-73
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OCT-VALUE 74-80
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NOV-VALUE 81-87
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DEC-VALUE 88-94
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