TIME BIAS CORRECTED DIVISIONAL TEMPERATURE-PRECIPITATION-DROUGHT INDEX (TD-9640) MARCH 1992 The major parameters in this data set are sequential "Time Biased Corrected" state climatic division monthly Average Temperatures (Deg. F. to 10ths), Precipitation (Inches to 100ths), and Palmer Drought Indices (PDSI, PHDI, PMDI, and ZNDX). Period of record is 1895 through 1993. Monthly averages within a climatic division have been calculated by giving equal weight to stations reporting both temperature and precipitation within a division. In the U.S., observers at cooperative stations often take one observation per day, and the ending time of the climatological day at any station can vary from station-to-station as well as year-to-year. Differences of the 24- hour period over which each observer reports his or her maximum and minimum temperature as well as the average temperature [(max + min)/2] affects the calculated monthly mean temperature. Karl, et al. (1986), describe the biases that this introduces. These potential biases were rectified by adjusting for these varying observation times. The model described by Karl, et al. (1986), was used to adjust the climate division averages such that all stations end their climatological day at midnight; i.e., climatological day coincides with calendar day. The time of observation was determined at each station within a climate division during January of the years 1931, 1941, 1951, 1965, 1975, and 1984 for the states of California, Colorado, Illinois, Indiana, New York, North Carolina, and Washington. The fraction of observers recording at various hours of the day was calculated and interpolated for intervening years (extrapolated for subsequent years). For these seven states, the ending time of observation was grouped into three categories: AM, PM, and MD. The AM category included observers who ended their climatological day between 3 AM and 11AM; the PM category between noon and 9 PM; and the MD category between 10 PM and 2 AM; all local standard time. The fraction of observers in these categories was calculated, and it was assumed the 7 AM observation time best represented the AM category; the 5 PM observation time, the PM category; and midnight for the MD category. The reason for the simplification was to test if a faster method, requiring significantly less bookkeeping and keypunching, could not provide nearly as good results as calculating the fraction of observers at each of the 24 hours of the day. The time of observation bias model was run by using the latitude and longitude of each of the centroids of the climate divisions. The output from the model was the time of observation bias, with respect to a midnight-to-midnight climatological day, for each of the possible ending hours of the climatological day. Each climate division's monthly average was then adjusted by weighting the bias at any given hour by the fraction of stations within the climate division observing at that hour, and subtracting the result for the reported monthly mean temperature. Differences of the biases were small (< 0.3 Deg. F.) for those calculated by categorizing the ending time of observation into three categories compared to those obtained from calculating the fraction of stations with observation times at each of the 24 hours of the day. This is attributed to the preponderance of AM observation times falling between 6 AM and 9 AM, and PM observation times falling between 4 PM and 7 PM. As a result, by assuming 7 AM observation for all AM stations and 5 PM for all PM stations, a good estimate of the median bias is obtained for all AM or PM observations. Furthermore, nearly all the MD stations observed at midnight. It should also be noted that the borders of the climate divisions in 1951 were not consistent with those defined in 1965. Due to the substantial additional effort it would have required locating each station within three or four climate divisions, as defined today, the change in the statewide percentage of AM, PM, and MD observation times was applied in equal proportions to all climate divisions prior to and including 1951. Based on small differences between the two methods of estimating the time of observation bias, the simpler categorical procedure was used for all climate divisions. This should effectively eliminate most of the biases (over 2 Deg. F.) in some climate divisions that have become part of the divisional averages. These biases affect both trends and actual estimates of divisional averages. Reference Karl, et al. (1986): "A model to estimate the time of observation bias associated with monthly mean maximum, minimum, and mean temperatures for the United States" (Thomas R. Karl, Claude N. Williams, Jr., and Pamela J. Young, National Climatic Data Center, and Wayne M. Wendland, Illinois State Water Survey, Journal of Climate and Applied Meteorology, January 1986, American Meteorological Society, Boston, MA). The time of observation bias model which can be used for the maximum, minimum, and mean monthly temperature at any location in the contiguous U.S. [program NCC*F11SRC (OBTBIAS Code) and NCC*F11REL (OBTBIAS)], is available for purchase from the NCDC. Historical drought data have been added to this file for the period 1895 to present. The file is updated monthly. All drought data are calibrated using the period 1895-1987 (cf. Karl, 1986; Journal of Climate and Applied Meteorology, Vol. 25, No. 1, January 1986). Drought data include: 1. Palmer Drought Severity Index (PDSI) This is the monthly value (index) that is generated indicating the severity of a wet or dry spell. This index is based on the principles of a balance between moisture supply and demand. Man-made changes were not considered in this calculation. The index generally ranges from -6 to +6, with negative values denoting dry spells and positive values indicating wet spells. There are a few values in the magnitude of +7 or -7. PDSI values 0 to -.5 = normal; -0.5 to -1.0 = incipient drought; -1.0 to -2.0 = mild drought; - 2.0 to -3.0 = moderate drought; -3.0 to -4.0 = severe drought; and greater than -4.0 = extreme drought. Similar adjectives are attached to positive values of wet spells. This is a meteorological drought index used to assess the severity of dry or wet spells of weather. 2. Palmer Hydrological Drought Index (PHDI) This is the monthly value (index) generated monthly that indicates the severity of a wet or dry spell. This index is based on the principles of a balance between moisture supply and demand. Man-made changes such as increased irrigation, new reservoirs, and added industrial water use were not included in the computation of this index. The index generally ranges from -6 to +6, with negative values denoting dry spells, and positive values indicating wet spells. There are a few values in the magnitude of +7 or -7. PHDI values 0 to -0.5 = normal; -0.5 to -1.0 = incipient drought; -1.0 to -2.0 = mild drought; -2.0 to -3.0 = moderate drought; -3.0 to -4.0 = severe drought; and greater than -4.0 = extreme drought. Similar adjectives are attached to positive values of wet spells. This is a hydrological drought index used to assess long-term moisture supply. 3. Palmer "Z" Index (ZNDX) This is the generated monthly Z values, and they can be expressed as the "Moisture Anomaly Index." Each monthly Z value is a measure of the departure from normal of the moisture climate for that month. This index can respond to a month of above-normal precipitation, even during periods of drought. Table 1 contains expected values of the Z index and other drought parameters. See Historical Climatology Series 3-6 through 3-9 for a detailed description of the drought indices. 4. Modified Palmer Drought Severity Index (PMDI) This is a modification of the Palmer Drought Severity Index. The modification was made by the National Weather Service Climate Analysis Center for operational meteorological purposes. The Palmer drought program calculates three intermediate parallel index values each month. Only one value is selected as the PDSI drought index for the month. This selection is made internally by the program on the basis of probabilities. If the probability that a drought is over is 100%, then one index is used. If the probability that a wet spell is over is 100%, then another index is used. If the probability is between 0% and 100%, the third index is assigned to the PDSI. The modification (PMDI) incorporates a weighted average of the wet and dry index terms, using the probability as the weighting factor. (Thomas R. Heddinghause and Paul Sabol, 1991; "A Review of the Palmer Drought Severity Index and Where Do We Go From Here?," Proceedings of the Seventh Conference on Applied Climatology, pp. 242-246, American Meteorological Society, Boston, MA). The PMDI and PDSI will have the same value during an established drought or wet spell (i.e., when the probability is 100%), but they will have different values during transition periods. Table 1 Classes for Wet and Dry Periods Approximate Cumulative Frequency Range Range % PHDI Category Z > 96 > 4.00 Extreme wetness > 3.50 90-95 3.00, 3.99 Severe wetness 3.50, 3.49 73-89 1.50, 2.99 Mild to moderate wetness 1.00, 2.49 28-72 -1.49, 1.49 Near normal -1.24, 0.99 11-27 -1.50, -2.99 Mild to moderate drought -1.25, -1.99 5-10 -3.00, -3.99 Severe drought -2.00, -2.74 < 4 <-4.00 Extreme drought <-2.75 The data set contains 6 files: File 1. Divisional Monthly Palmer Drought Severity Index (PDSI) File 2. Divisional Monthly Palmer Hydrological Drought Index (PHDI) File 3. Divisional Monthly Palmer "Z" Index (ZNDX) File 4. Divisional Monthly Modified Palmer Drought Severity Index (PMDI) File 5. Divisional Monthly Temperatures File 6. Divisional Monthly Precipitation FILE 1. DIVISIONAL MONTHLY PALMER DROUGHT SEVERITY INDEX (PDSI) Element Record Name Position Element Description FILLER 1 Blank STATE-CODE 2-3 STATE CODE as indicated in the State- Code Table. Range of values of 01- 91. 01 Alabama 28 New Jersey 02 Arizona 29 New Mexico 03 Arkansas 30 New York 04 California 31 North Carolina 05 Colorado 32 North Dakota 06 Connecticut 33 Ohio 07 Delaware 34 Oklahoma 08 Florida 35 Oregon 09 Georgia 36 Pennsylvania 10 Idaho 37 Rhode Island 11 Illinois 38 South Carolina 12 Indiana 39 South Dakota 13 Iowa 40 Tennessee 14 Kansas 41 Texas 15 Kentucky 42 Utah 16 Louisiana 43 Vermont 17 Maine 44 Virginia 18 Maryland 45 Washington 19 Massachusetts 46 West Virginia 20 Michigan 47 Wisconsin 21 Minnesota 48 Wyoming 22 Mississippi 49 Not Used 23 Missouri 50 Alaska 24 Montana 51 Hawaii 25 Nebraska 66 Puerto Rico 26 Nevada 67 Virgin Islands 27 New Hampshire 91 Pacific Islands DIVISION NUMBER 4-5 DIVISION NUMBER - Assigned by NCDC. Range of values 01-10. FILLER 6 Blank YEAR 7-10 This is the year of record. Range is 1895 to current year processed. JAN-VALUE 11-17 JANUARY Divisional Monthly "PDSI". Range of values b-20.00 to bb20.00. Decimal point retains a position in 7-character field. Missing values in the latest year are indicated by - 999.99. FEB-VALUE 18-24 FEBRUARY Divisional Monthly "PDSI". MAR-VALUE 25-31 MARCH Divisional Monthly "PDSI". APR-VALUE 32-38 APRIL Divisional Monthly "PDSI". MAY-VALUE 39-45 MAY Divisional Monthly "PDSI". JUNE-VALUE 46-52 JUNE Divisional Monthly "PDSI". JULY-VALUE 53-59 JULY Divisional Monthly "PDSI". AUG-VALUE 60-66 AUGUST Divisional Monthly "PDSI". SEPT-VALUE 67-73 SEPTEMBER Divisional Monthly "PDSI". OCT-VALUE 74-80 OCTOBER Divisional Monthly "PDSI". NOV-VALUE 81-87 NOVEMBER Divisional Monthly "PDSI". DEC-VALUE 88-94 DECEMBER Divisional Monthly "PDSI". FILE 2. DIVISIONAL MONTHLY PALMER HYDROLOGICAL DROUGHT INDEX (PHDI) Element Record Name Position Element Description FILLER 1 Blank STATE-CODE 2-3 STATE-CODE as indicated in State Code Table as described in FILE 1. Range of values is 01-91. DIVISION-NUMBER 4-5 DIVISION NUMBER - Assigned by NCDC. Range of values 01-10. FILLER 6 Blank YEAR 7-10 This is the year of record. Range is 1895 to current year processed. JAN-VALUE 11-17 JANUARY Monthly Divisional "PHDI". Range of values b-20.00 to bb20.00. Decimal point retains a position in 7-character field. Missing values in the latest year are indicated by - 999.99. FEB-VALUE 18-24 FEBRUARY Monthly Divisional "PHDI". MAR-VALUE 25-31 MARCH Monthly Divisional "PHDI". APR-VALUE 32-38 APRIL Monthly Divisional "PHDI". MAY-VALUE 39-45 MAY Monthly Divisional "PHDI". JUNE-VALUE 46-52 JUNE Monthly Divisional "PHDI". JULY-VALUE 53-59 JULY Monthly Divisional "PHDI". AUG-VALUE 60-66 AUGUST Monthly Divisional "PHDI". SEPT-VALUE 67-73 SEPTEMBER Monthly Divisional "PHDI". OCT-VALUE 74-80 OCTOBER Monthly Divisional "PHDI". NOV-VALUE 81-87 NOVEMBER Monthly Divisional "PHDI". DEC-VALUE 88-94 DECEMBER Monthly Divisional "PHDI". FILE 3. DIVISIONAL MONTHLY PALMER "Z" INDEX (ZNDX) Element Record Name Position Element Description FILLER 1 Blank STATE-CODE 2-3 STATE-CODE as indicated in State Code Table as described in FILE 1. Range of values is 01-91. DIVISION-NUMBER 4-5 DIVISION NUMBER - Assigned by NCDC. Range of values 01-10. FILLER 6 Blank YEAR 7-10 This is the year of record. Range is 1895 to current year processed. JAN-VALUE 11-17 JANUARY Monthly Divisional "ZNDX". Range of values b-20.00 to bb20.00. Decimal point retains a position in 7-character field. Missing values in the latest year are indicated by - 999.99 FEB-VALUE 18-24 FEBRUARY Monthly Divisional "ZNDX". MAR-VALUE 25-31 MARCH Monthly Divisional "ZNDX". APR-VALUE 32-38 APRIL Monthly Divisional "ZNDX". MAY-VALUE 39-45 MAY Monthly Divisional "ZNDX". JUNE-VALUE 46-52 JUNE Monthly Divisional "ZNDX". JULY-VALUE 53-59 JULY Monthly Divisional "ZNDX". AUG-VALUE 60-66 AUGUST Monthly Divisional "ZNDX". SEPT-VALUE 67-73 SEPTEMBER Monthly Divisional "ZNDX". OCT-VALUE 74-80 OCTOBER Monthly Divisional "ZNDX". NOV-VALUE 81-87 NOVEMBER Monthly Divisional "ZNDX". DEC-VALUE 88-94 DECEMBER Monthly Divisional "ZNDX". FILE 4. DIVISIONAL MONTHLY MODIFIED PALMER DROUGHT SEVERITY INDEX (PMDI) Element Record Name Position Element Description FILLER 1 Blank STATE-CODE 2-3 STATE-CODE as indicated in State Code Table as described in FILE 1. Range of values is 01-91. DIVISION-NUMBER 4-5 DIVISION NUMBER - Assigned by NCDC. Range of values 01-10. FILLER 6 Blank YEAR 7-10 This is the year of record. Range is 1895 to current year processed. JAN-VALUE 11-17 JANUARY Monthly Divisional "PMDI". Range of values b-20.00 to bb20.00. Decimal point retains a position in 7-character field. Missing values in the latest year are indicated by - 999.99. FEB-VALUE 18-24 FEBRUARY Monthly Divisional "PMDI". MAR-VALUE 25-31 MARCH Monthly Divisional "PMDI". APR-VALUE 32-38 APRIL Monthly Divisional "PMDI". MAY-VALUE 39-45 MAY Monthly Divisional "PMDI". JUNE-VALUE 46-52 JUNE Monthly Divisional "PMDI". JULY-VALUE 53-59 JULY Monthly Divisional "PMDI". AUG-VALUE 60-66 AUGUST Monthly Divisional "PMDI". SEPT-VALUE 67-73 SEPTEMBER Monthly Divisional "PMDI". OCT-VALUE 74-80 OCTOBER Monthly Divisional "PMDI". NOV-VALUE 81-87 NOVEMBER Monthly Divisional "PMDI". DEC-VALUE 88-94 DECEMBER Monthly Divisional "PMDI". FILE 5. DIVISIONAL MONTHLY TEMPERATURES Element Record Name Position Element Description STATE-CODE 1-2 STATE-CODE as indicated in State Code Table as described in FILE 1. Range of values is 01-91. DIVISION-NUMBER 3-4 DIVISION NUMBER - Assigned by NCDC. Range of values 01-10. YEAR 5-8 This is the year of record. Range is 1895 to current year processed. JAN-VALUE 9-13 JANUARY Monthly Divisional Temperature Value. Range of values - 50.0 to 140.0 degrees Fahrenheit. Decimals retain a position in the 5- character field. Missing values in the latest year are indicated by - 99.9. FEB-VALUE 14-18 FEBRUARY Monthly Divisional Temperature Value. MAR-VALUE 19-23 MARCH Monthly Divisional Temperature Value. APR-VALUE 24-28 APRIL Monthly Divisional Temperature Value. MAY-VALUE 29-33 MAY Monthly Divisional Temperature Value. JUNE-VALUE 34-38 JUNE Monthly Divisional Temperature Value. JULY-VALUE 39-43 JULY Monthly Divisional Temperature Value. AUG-VALUE 44-48 AUGUST Monthly Divisional Temperature Value. SEPT-VALUE 49-53 SEPTEMBER Monthly Divisional Temperature Value. OCT-VALUE 54-58 OCTOBER Monthly Divisional Temperature Value. NOV-VALUE 59-63 NOVEMBER Monthly Divisional Temperature Value. DEC-VALUE 64-68 DECEMBER Monthly Divisional Temperature Value. FILLER 69-94 Blanks FILE 6. DIVISIONAL MONTHLY PRECIPITATION Element Record Name Position Element Description STATE-CODE 1-2 STATE-CODE as indicated in State Code Table as described in FILE 1. Range of value is 01-91. DIVISION-NUMBER 3-4 DIVISION NUMBER - Assigned by NCDC. Range of values 01-10. YEAR 5-8 This is the year of record. Range is 1895 to current year processed. JAN-VALUE 9-13 JANUARY Monthly Divisional Precipitation Value. Range of values 00.00 to 99.99. Decimal point retains a position in the 5-character field. Missing values in the latest year are indicated by -9.99. FEB-VALUE 14-18 FEBRUARY Monthly Divisional Precipitation Value. MAR-VALUE 19-23 MARCH Monthly Divisional Precipitation Value. APR-VALUE 24-28 APRIL Monthly Divisional Precipitation Value. MAY-VALUE 29-33 MAY Monthly Divisional Precipitation Value. JUNE-VALUE 34-38 JUNE Monthly Divisional Precipitation Value. JULY-VALUE 39-43 JULY Monthly Divisional Precipitation Value. AUG-VALUE 44-48 AUGUST Monthly Divisional Precipitation Value. SEPT-VALUE 49-53 SEPTEMBER Monthly Divisional Precipitation Value. OCT-VALUE 54-58 OCTOBER Monthly Divisional Precipitation Value. NOV-VALUE 59-63 NOVEMBER Monthly Divisional Precipitation Value. DEC-VALUE 64-68 DECEMBER Monthly Divisional Precipitation Value. FILLER 69-94 Blanks