How to download weather data from CIMIS web site?

Te California Irrigation Management Information System (CIMIS) is a program in the Office of Water Use Efficiency (OWUE), California Department of Water Resources (DWR) that manages a network of over 120 automated weather stations in the state of California. CIMIS was developed in 1982 by the California Department of Water Resource and the University of California at Davis to assist California’s irrigators manage their water resources efficiently.

1. Point your web browser to:

http://www.cimis.water.ca.gov/cimis/frontDailyReport.do

A Logon screen appears:

For user name enter: PCRANCH. For password enter: Pa$$w0rd The “o” in password is actually “zero”, and click the “Submit” key. The site of CIMIS appears.

2. For the “Station List”, select an entry, for example : “2-FivePoint, Since June/1982"

3. Click the “Select Sensors” check box and a list of sensors appears:

For the “sensor List”, select the following seven sensors:

a. 1-Solar Radiation Average
b. 6-Maxium Air Temperature
c. 7-Minimum Air Temperature
d. 8-Average Air Temperature
e. 14-Average Wind Speed
f. 23-Percipitation
g. 33-Average Relative Humidity

To select more than on entry, hold down the control key and click on a selection.

4. For the “Unit”, select Metric:

5. For the “End Date”, enter January 1, 2008. For the “Start Date” enter 1/6/1982, which is the starting date of the data collection for that weather station. Enter different Start Date for different stations, but always use the same ending date, which in this case is January 1, 2008:

6. For “Report Method”, select the “CSV with Headers” option:

7. Finally click the “Submit” button. The computer asks you for a file name for saving data. The file name must start with the word CIMIS and then an underscore and then a number such as 2. The extension for the file must be CSV (Comma Separated Values). For example: CIMIS_2.CSV

This naming method is very important, because our Convert program looks for files like CIMIS_*.CSV . Save your file in a folder called C:\CIMIS\

8. Repeat steps 3 through 8 for other weather stations. Sometimes, you can select multiple weather stations from the Station List by holding down the Control Key and clicking on more than one entry. Try to not select more than three stations, otherwise, the web site refuses to process your request and displays an error message.

9. The download file has 19 columns, separated from each the by comma:

Stn Id
Station
Region
Date
Jul
qc
Sol Rad (W.sq.m)
qc
Max Air Temp (°C)
qc
Min Air Temp (°C)
qc
Avg Air Temp (°C)
qc
Avg wSpd (m/s)
qc
Precip (mm)
qc
Avg Rel Hum (%)

The "qc" stands for Quality Control and contains special codes related to the value of the next column. For example the code M means missing. For a complete list of codes visit the CIMIS web site. As you see, the computer adds several columns besides the seven columns you specified in the Sensor List, such as Stn Id, Station, Region, Date, Jul (Julian Date) and seven extra qc columns for quality control.

Conversion to PCRANCH format

After you have downloaded all weather data, copy the downloaded file onto the ‘Source’ folder of the Weather Processing Program (WPP) and run the WPP program. The convert program extracts and renames each weather data properly and stores them in the ‘Destination’ folder of the convert program. Copy the weather files from WPP's destination folder onto PCRANCH's 'W' folder The converted file name is named by using the Station Number, Station Name, and Starting and Ending dates. For Example:

ACT_005_Davis_05_06_2003_TO_12_19_2007.txt

The file name starts with the word ACT or AVG. which stands for Actual or Average weather. Then there is the station Id number, such as 005. Then there is the station name, such as Davis. Then there is the start date, such as 05_06_2003 (MM/DD/YYYY). Then there is the end date, such as 12_19_2007 (MM/DD/YYYY). The start and end dates are determined from the content of the weather data and not from the start and end dates you specified in the web page. There are two copies of the converted file: The first one is a tab delimited file with .TXT extension which is used by PCRANCH. The second one is a comma separated file with .CSV extension which is NOT used by PCRANCH. This file is created for your inspection and can be opened by the Excel program.

Missing Value Calculation

• Daily Average Solar Radiation - Replace the R and S flag with M flag (M = Missing)
• Daily Air Temperature - Replace the R, S, and Y flag with M flag (M = Missing)
• Daily Average Wind Speed - Replace S, R and Y codes with M code (M=Missing)
• Daily Precipitation - Replace R and S codes with M code (M=Missing)
• Daily Average Relative Humidity - I do not know how to quality control this field

If the missing value is for one day, then it is replaced by interpolating between yesterday and tomorrow values. If more than one day is missing, it is replaced by the average value for that day over the entire period of weather data.

Conversion factor

Convert solar radiation from w/sq m to cal/cm2/d by multiplying it with 2.0592. Convert wind speed from m/s to km/h by multiplying it with 3.6. The temperature is already in metric system. The relative humidity is in percentage and hence do not need to be converted.

The PCRANCH Weather File Format

The weather file is a tab delimited txt file. The first line contains the column headings. Each line thereafter contains the weather data for one day. The weather file must be in date order and must cover the time period for the simulation at minimum (it may cover a longer time period). All weather fields must be supplied for every day of this period (no missing values). The weather data is always in Metric system, regardless of the system you have selected for the program.

mes	dia	year	Mean Temp	Min Temp	Max Temp	Rad	Wind	RelHumidity	Rain
1	1	1989	4.75	-1.1	10.6	156.8	35.24722105	38.05833333	0
1	2	1989	4.7	-0.6	10	194	25.53176842	37.85735294	0
1	3	1989	5.55	-0.6	11.7	187.8	9.278526316	36.70294118	0
1	4	1989	3.35	0	6.7	171.3	10.24181053	38.82916667	0
1	5	1989	7.5	2.2	12.8	202.2	9.182273684	37.11111111	8.376
1	6	1989	3.9	-2.2	10	175.4	10.67437895	37.11617647	1.269

The file has ten columns:

1. mes, Month of the year (1-12)
2. dia, Day of the month (1-31)
3. Year (yyyy)
4. Mean daily temperature (C)
5. Minimum daily temperature (C)
6. Maximum daily temperature (C)
7. Total solar radiation (cal/cm2/d)
8. Mean daily wind speed (km/h)
9. Mean daily relative humidity (1-100)
10. Total daily rainfall (mm)

PCRANCH automatically extracts the rows from this file that cover the simulation period.