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How to Manage Pests

Degree-Days: Using the Calculator

This degree-day calculator has two branches. You can run preset models that have been recommended by UC Cooperative Extension, or you can specify the thresholds and method of calculation for any model. Weather data for the calculations may come from the UC IPM database for California, a file you supply, or data you enter online.

Specify source of temperature data

Weather data for the calculations may come from the UC IPM database for California, a file you supply, or data you enter online.

Data from UC IPM weather database

The database originated in 1980 as part of the original IMPACT online computer system and stores both current and historical daily weather data for approximately 350 weather stations throughout California. In 1996 it was converted to run on a new computer, with access through the World Wide Web.

Overview of variables, time periods, and averages available for Automatic, TouchTone, Climate, and PestCast stations
Station Type Automatic
(approx. 100 stations)
TouchTone
(approx. 40 stations)
Climate
(approx. 135 stations)
PestCast
(approx. 40 stations)
Source of data DWR (CIMIS) Volunteers NOAA UC and Cooperators
Period of record stored 6/82 to present or when available 8/81 to present or when available 1951 to present (6-month delay) 1995 to present or when available
Variables available avgs. available avgs. available avgs. available avgs.
Air temperature, maximum X X* X* X* X X (30-yr.) X
Air temperature, minimum X X* X* X* X X (30-yr.) X
Soil temperature, maximum X X* X* X* X*
Soil temperature, minimum X X* X* X* X*
* = where available
  1. Select the county in which you're interested. Choose from California's 58 counties.
  2. Select a weather station from the list of stations available in the selected county. A table lists the temperature variables and time period for which data are stored, and whether long-term averages have been calculated and are available. In case your selected county doesn't have the station you're looking for, tables of stations located in surrounding counties are also shown.
  3. Select a time period, a range of dates. From the lists, indicate the first date (month, day, and year) for which you want to calculate degree-days, and the last date (month, day, and year).
    • The default dates supplied by the computer are usually March 15 of the current year and the last date for which the selected station can be expected to have data.
    • To add long-term averages (as a climatological "forecast") to the end of your data request, indicate an ending date that is in the future, beyond yesterday's date.
  4. Select the temperature variable and backup stations. The Step 5 table includes the variables stored for the selected station, and below it is some additional information about the measurements that may be helpful. In the table, click on the radio button next to a variable name to mark it for retrieval. The request for data will be filled first from the selected station, then from the backup and long-term average stations, left to right.
    • Backup stations. Backup stations listed in the table are nearby stations that can be used to fill in data gaps. Shown will be either a station name or "none recommended."
      • When a station is listed, do nothing if you want it to supply data when data from the selected station is missing. If you do not want to include substitutes for missing data, click on the backup station name and select "do not fill gaps."
      • If "none recommended" is shown, no station is considered to be similar enough to the selected station to be used as a backup.
      • Backup station 1 is used first to supply missing data; if the data value for the date is also missing in Backup station 1, Backup station 2 will be used. Any data gaps will be filled in from the backup stations, if possible.
    • Long-term average station. If a data value for a date is not available from the selected station or either of the backup stations, the long-term average for the date will be used if a station is recommended in the table.
      • All stations have a recommended long-term average for air temperature, and some have a recommended average for soil temperature.
      • If you do not wish for long-term averages to be used to fill in data gaps, click on the station name and select "do not fill gaps."
      • "Forecasts" based on long-term averages can be included if you specify a time period that includes dates in the future.
    Note: If there are data gaps in the file when data are retrieved, the accumulation will start over after each gap.
  5. Select the output format. The calculation can be presented in two formats:
    • Formatted report (for viewing or printing) includes max/min temperatures, daily degree-days, and accumulated degree-days for each value in a table with column headings, and indicates the source of any data that were supplied by a backup or long-term average station.
    • Comma-delimited data file (for use with spreadsheets) displays a text file of data, with values separated by commas. The file can be saved to your disk and then imported into a spreadsheet program.
  6. Press the CALCULATE DEGREE-DAYS button to complete the calculation.

Special note. Saving these specifications to use them again without having to repeat every step is easy. Use the save as (or equivalent) command in your browser and save the document as "source." To submit the file again, start your browser, use the "Open file" (or equivalent) command, make any necessary changes such as the time period, then press the CALCULATE DEGREE-DAYS button.

Data from your file

You may enter your own temperatures into a file and then use that file to calculate degree-days. Temperatures may be entered in Fahrenheit or Celsius; you will be asked to specify the units when you calculate degree-days.

To be correctly interpreted, note the following requirements for the data file.

  • The file must be a text file.
  • Data values must be separated by either a comma or a tab character.
  • Be prepared to supply the position of date, minimum temperature and maximum temperature in a row. (The position must be the same for every row of data.)
  • Each day's temperatures must be on a separate line in the file.
  • Any row in the file that begins with a double-quote mark (") or a single-quote mark (') will be treated as a comment and ignored in the calculations.

For more information about preparing the file, see Format for Data File for Degree-day Calculations.

To specify the file, press the Browse button and locate the file on your computer.

Data you enter online

With this option you may enter maximum and minimum temperature pairs directly into a form on the Web.

Run models or calculate degree-days

To calculate degree-days you must select a model or thresholds and method of calculation, in addition to supplying temperature data.

NOTE: Are you retrieving data regularly, perhaps as often as daily or weekly? See the Special note below on reusing these specifications.

Click on one of the models, then press the Run model button. If the model you're interested in isn't listed, enter the lower (and upper) threshold(s), specify whether the threshold is in Fahrenheit or Celsius, select the calculation and upper cutoff methods if you wish, then click on the Calculate button.

Special note. Saving these specifications to use them again without having to repeat every step is easy. Use the save as (or equivalent) command in your browser and save the document as "source." To submit the file again, start your browser, use the "Open file" (or equivalent) command, make any necessary changes such as the time period, and then press the CALCULATE DEGREE-DAYS button.

Reports

Reports include the data for the selected station over the requested time period, in the units and format specified. In any format, the output includes

  • information about the selected station and its variables
  • a "retrieval report" that indicates the number of data values supplied by the selected station and any backup or long-term average stations
  • a description of the file format
  • the data that were retrieved and the degree-days that were calculated

Formatted report

Column headings make this report easy to read. The source of each temperature is indicated immediately following the value (in the column headed by a "*"). When a temperature is from the selected station, the column is blank; if the value is not supplied by the selected station, a code (1, 2, or A) indicates the source of the value: backup station 1, backup station 2, or the long-term average station.

Comma-delimited data file

This format uses the quote character ("), recognized by most spreadsheets, to designate information documenting the calculation results and file format. Otherwise, values for each date are separated by commas, and can be imported into spreadsheet or database software for further processing or analysis.

To save the data page as a file that can be used with a spreadsheet or database program, use your browser's "save as" command (usually on the File menu), specify a descriptive name if you wish, and save the file as text. You can also select all of the data displayed, copy and paste it to a new document in a text editor or word processor, and then save it as text.

The file is a text file, in the following format.

VARIABLE DESCRIPTION UNITS
1 Station code  
2 Date: year,month,day yyyymmdd
3 Air temperature, maximum Fahrenheit
4 Air temperature, minimum Fahrenheit
5 Soil temperature, maximum Fahrenheit
6 Soil temperature, minimum Fahrenheit
7 Degree-days Fahrenheit
8 Accumulated degree-days Fahrenheit

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Statewide IPM Program, Agriculture and Natural Resources, University of California
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