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Cligen Overview
Cligen is a stochastic weather generator which produces daily estimates of precipitation, temperature, dewpoint, wind, and solar radiation for a single geographic point, using monthly parameters (means, SD's, skewness, etc.) derived from the historic measurements. Unlike other climate generators, it produces individual storm parameter estimates, including time to peak, peak intensity, and storm duration, which are required to run the WEPP and the WEPS soil erosion models. Station parameter files to run Cligen for several thousand U. S. sites are available for download from this website: also data and software to build station files for international sites. With the exception of Tmin, Tmax, and Tdew temperatures (changed in January 2004), daily estimates for each parameter are generated independently of the others. With the current random number generator, subsequent runs on the same machine made with identical inputs will produce identical results.
Users of daily simulation models should consider the impacts of Cligen's characteristics on their application. Individual parameter distributions may be expected to reproduce monthly historic distributions quite well. However, if the model in question is sensitive to the daily interactions of two or more of the parameters Cligen produces, Cligen may not be the most appropriate weather generator to use. This is because for a given day, it generates solar radiation, and maximum and minimum temperatures completely independently from precipitation. Experience and common sense tell us that these parameters are NOT independent. In practice this may not be a huge issue, since it is not uncommon for models to be sensitive to one weather parameter on a daily basis, and relatively insensitive to the others, as long as their monthly trends are preserved.
Programs and Source Code
Cligen Windows prebuilt executables:
- Cligen 4.2 - From 1997.
- Cligen 4.3 - From 1998, allowed runs to be made using a single station file.
- Cligen 5.3 - From 2008, Addition of QA/QC control. Corrected dew point calculation for a type 6 run. Dew point was not being calculated from tmin and tmax values read from the observed input.
- Cligen 5.32 - From 2013, Changed order of reading in wet/wet & wet/dry Equivalence statement had interleaved the values making them incorrect Affected only Yoder-Foster & Fourier interpolation From WEPS 5.30001
- Cligen 5.322 - From 2018-2022, Fix for leap years to include years divisible by 400 but not divisible by 100. Corrected calculation of Coefficient of Variation so a zero monthly average temperature does not cause a divide by zero.
Source is available for the following Cligen versions:
Cligen 5 all versions: https://github.com/jfrankenberger/cligen5
Cligen 4 all versions: https://github.com/jfrankenberger/cligen4
Data Files
parfiles-1995.zip - All US CLIGEN Stations .PAR files from the 1995 release. Varying periods of records between stations. These files can be used with Cligen versions 4.3 and 5.3.
An inventory of the station PAR files contained in the 1995 archive can be found in stations1995.txt For each station the file contains the state abbreviation; staition name; station number; latitude; longitude; years of record; elevation(ft).
parfiles-2015.zip - All US CLIGEN Stations .PAR files from the 2015 CLIGEN database update. These files all have the same 40 year period of record 1974-2013. These files can be used with Cligen versions 4.3 and 5.3.
An inventory of the station PAR files contained in the 2015 archive can be found in stations2015.txt For each station the file contains the state abbreviation; station name; station number; latitude; longitude; years of record; elevation(ft).
Worldwide CLIGEN PAR files - This dataset, available from data.gov, represents CLIGEN input parameters for locations in 68 countries. To use these PAR files in the WEPP Windows interface the station(s) of interest can be copied to the WEPP directory. The cligen-import-par-files.pdf file outlines the steps to do this.
V42data.zip - All CLIGEN Stations .PAR older files compatible with Cligen version 4.2. Each state is a file containing the PAR data for every station in the state. Not compatible with CLIGEN 4.3 or 5.3
Note than when downloading the WEPP Model the Cligen program and data files for 1995 and 2015 are already included.
The format of the .PAR input files used in Cligen are described in the document cligenparms.pdf.
Running Cligen
These steps are for running CLIGEN directly from a command line without the WEPP Windows interface.
- Find the station of interest in either the stations1995.txt file or the stations2015.txt file depending on which CLIGEN database is being used. Using the state abbreviation and staion number combine to makeup the PAR file name. For example: the line in stations file is:
"in";"LAFAYETTE 5 S IN";124715;40.35;-86.87;40;600.00
Would refer to the PAR file in124715.par. - Copy the par file to your directory which contains the Cligen executable.
- Run Cligen using the '-i' option.
For example:
cligen -b1 -y30 -iin124715.par -oLAFptest
Runs a 30-year simulation for Lafayette, Indiana, using "in124715.par" as the station parameter file, and puts the output into "LAFptest".
Cligen Publications
2019. Updated climate database and impacts on WEPP model predictions
2007. Implementing quality control on a random number stream to improve a stochastic weather generator.
1995. WEPP Model Documentation - Chapter 2 - Weather Generator.
How Cligen Works
The following document: CligenDesription.pdf describes the basics of Cligen and the development history.
The revisions to Cligen between versions 4 and 5 are outlined in the slideshow in the document: cligenslds.pdf
Cligen History
Cligen was produced by Arlin Nicks and Gene Gander at the USDA Agricultural Research Service (ARS) lab in Durant, Oklahoma. They made their last significant changes to the model in the mid 1990's before Dr. Nicks' retirement and death in July 1997. David Hall and Dayna Scheele at the USDA Forest Service lab in Moscow, Idaho, acquired code from Dr. Nicks' computer to generate from historical weather data, the monthly station parameter files required to drive Cligen. They mechanically cleaned the existing station data files, and added a large number of new stations for the United States. In the Summer of 1999 Bofu Yu of Griffith University in Australia, expressed concerns that Cligen's rainfall intensity calculations were not operating correctly due to a unit conversion error, and offered revised code to correct the problem. In the Fall of 1999, Charles R. Meyer at the USDA-ARS lab in West Lafayette, Indiana, re-coded the CLIGEN source code to make it understandable, maintainable, and extensible by people who had not written it. He incorporated Dr. Yu's corrections. When performing checks on CLIGEN's uniform random number generator and standard normal generator, Meyer discovered that they were not operating correctly. A paper by Johnson, et. al. (Stochastic Weather Simulation: Overview and Analysis of Two Commonly Used Models; Journal of Applied Meteorology, Vol. 35, October 1996), reports effects which appear to be the result of this problem. This has major implications for any stochastic model like CLIGEN because all its output originates from its random number generator. To correct this problem Meyer introduced a form of "quality control" borrowed from industrial engineering leading to Version 5 of Cligen.
