Weather data can come from these kinds of sources:
The models require site-specific weather data in a format they understand. Century5 has its own text file format for monthly weather data, and also accepts a netCDF format. DayCent5 has its own text file format for daily weather data, and accepts spatial data in a netCDF file. Both models expect annual mean values by month in the site parameters for precipitation and minimum and maximum temperature, and can use these mean values rather than a data file.
Simulations use a weather data file when the "F" option is specified for "Weather choice" in a management schedule. Each schedule block, or block instance, can specify its own weather source. Weather data files have a year associated with each data record. At the start of a management block, the weather data server attempts to match the current simulation year with the weather data year. If a match is unavailable, the first year of the weather data is used for the first year of the management block.
The models need to know where weather data files are located.
If a weather data file is to be used (.sch file: "F Weather choice"), specify the file name in the schedule file on the next line after the weather choice. A path in the file name is optional; if supplied, then the path will be used. If the path is not supplied, then the path will be assumed to be the current directory, or the path specified in the WeatherDataPaths.txt, if that is present in the current directory (see below).
Another way to specify paths to directories containing weather data files, is to use a text file containing the paths. The paths are associated with a particular computer, allowing simulations to be run on different computers with the same, unmodified schedule file. Currently, the paths file must be named WeatherDataPaths.txt and be located in the directory where the simulation is run. Each line in the file can be either a comment (the first character is #) or a name=path pair. The name part is the name of the computer on which the simulation is running, such as returned in a Linux console with "uname -n" command, or in a Microsoft Windows command window with the VER command. If you have several computers that start with the same string, such as on a Linux cluster, then only the first common part of the node name is needed. A special system name is "any", which provides the default path if no matching system is found.
The site parameter weather values are describe in . The models' package contains utilities to help create these values:
| Utility | Source Data |
|---|---|
| CRUToSiteParameters | monthly CRU NetCDF file. |
| DailyWthr2SiteParams | daily weather text-format file. |
| MonthlyToSiteWeather | monthly weather text-format file. |
These statistics can also be calculated in your spreadsheet program. Enter the values into your site parameters file using a text editor.
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:
Use the mean values from the site parameters for each month in every simulation year of the block instance. (.sch file: "Weather choice" = "M")
Use 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. (.sch file: "Weather choice" = "S")
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. (.sch file: "Weather choice" = "F"; next line = weather data file name, and path if in a different location)
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. (.sch file: "Weather choice" = "C")
CENTURY uses mean monthly precipitation (PRECIP) and mean monthly minimum and maximum temperatures (TMN2M, TMX2M ) from the site parameters, and monthly data from a weather data file. However, if any PRECIP, TMN2M, or TMX2M parameter values are a missing value (less than -99) the weather site parameters will not be used.
Century5 can read monthly data from a text file whose format is described in the section Century Monthly Weather Data File . Monthly weather data in a netCDF file in COARDS format is also acceptable. This format is described in the section Monthly Weather Data in a netCDF File.
The daily weather data and file formats are described in the section Daily 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.