Weather Data

Monthly Weather Data

CENTURY uses mean monthly precipitation (PRECIP) and mean monthly minimum and maximum temperatures (TMN2M, TMX2M ) from the site parameters, and per-year monthly data from a weather data file.

For each block instance within a simulation's management schedule, the management editor allows you to choose from four options for the weather data source:

1. The first option uses the mean values from the site parameters for each month in every simulation year of the block instance.
2. The second option uses the mean monthly temperature values in every year, and stochastically generates precipitation from a skewed distribution (Nicks, 1974) using the PRCSKW and PRCSTD values from the site parameters. If skewness parameters are unavailable, a truncated normal distribution is used, but this will increase the overall mean precipitation when the coefficient of variation for precipitation is high.
3. The third option reads the monthly values for precipitation, minimum and maximum air temperature from the start of a weather data file. If the end of the file is reached, the data is reused from the start of the file.
4. The fourth option will continue reading from the current weather data file without first rewinding. You must have previously specified a file in an earlier block instance. As with option 3, if the end of the file is reached, the data is reused from the start of the file.

If a monthly value is missing from an actual weather file, it should be set equal to the value -99.99 within the file. When reading in this missing value flag, CENTURY will replace the flag as follows:

1. For minimum or maximum monthly temperature, the mean monthly value (TMN2M or TMX2M) from the site parameters will be used.
2. For a precipitation value, the skewed distribution value will be calculated if possible (if PRCSKW is not zero). Otherwise, the monthly mean precipitation (PRECIP) will be used.

FILE100, distributed with Century 4, can automatically analyze a CENTURY model weather file with monthly precipitation and temperatures and place the parameters for climate statistics in a Century 4 <site>.100 file. These statistics can also be calculated in your spreadsheet program; you will then manually enter the values into the site parameters using the site parameters editor in CMI.

In calculation of PET, Century sets the minimum allowable monthly temperature to be -10.0 C, and the minimum allowable monthly PET to be 0.5 cm month^-1. If a microcosm is being simulated, PET is fixed at 15.0 cm month^-1.

Daily Weather Data

The daily weather data and file formats are described in the section Daily Weather Data

Utilities to Manipulate Weather Data

Utility programs are provided with the Century distribution which allow you to manipulate weather files. You can view a list of these in the section Utilities.

See Also

Weather Data File
Site Parameters
Editing Site Management