A false zero is an incorrect report of zero precipitation during the rainy season. The false zeros mainly come from the conversion of file with a given format to another file format, in most cases, the missing values from the original file format are not flagged and left blank, when converting the file to the other format the missing values are replaced by zeros. To check the false zeros, the percentage of zero values for each month at the target station is computed and compared to the average of the percentage of zero values for the corresponding month of the neighbor stations. If this percentage is greater than a given threshold, this month is flagged as a month containing false zeros.

To perform false-zeros check for daily rainfall data, use the menu Quality Control ‣ False-Zeros Check for daily rainfall  . It will display a tabbed widget on the left panel, allows to enter the inputs data and parameters.

The tab   Data and Parameters     allows to enter the inputs data and set the parameters for the QC.




  1. Select from the drop-down list the file containing the daily rainfall station data to be checked if it is already loaded, or open it from the browse button on the right.

  2. Click on this button to set the parameters to be used for the false-zeros check. It displays a dialog box




  1. Specify the folder to save the results by browsing it from the button or typing the full path to the folder.
  2. Click the button       Check False-Zeros       to execute.

This creates a folder named FALSE.ZEROS.CHECK_data under the folder you provided (4) to save the results of the false zeros check. Inside this folder 2 directories and 1 file are created:

The tab   False-Zeros Output     allows to view the results of the false zeros check.




  1. If you already performed a false zeros check, you do not need to run it again, you can check this box, the input field below will be activated and you can provide the full path to FalseZeros.rds under the folder FALSE.ZEROS.CHECK_data by browsing it through the button on the right.
  2. The stations with a month containing false zeros are listed here. You can select a station and click on the button       View & Edit Result       to view the results. You can use the buttons   <<   or   >>   to switch to the previous or next station. It will open a table on the right panel showing the output of the false zeros for the selected station.



After verifying each month flagged as containing false zeros, if you find that the month does not have false zeros, you can remove it from the table by right-clicking on the column of row number corresponding to this month then from the pop menu click on Delete selected row  .




After editing this table, you have to save the changes you made. You can go to the menu File ‣ Save table   or click on the button in the toolbar to save the table. If the table is saved correctly, you should see an output message “Table saved successfully”.

  1. Select here the date corresponding to a month with false zeros to display the values of the rainfall data at the target station and the neighbor stations for this month. If you select the date from the drop-down list, click on the button   DISPLAY   to display the table. You can use the buttons   <<   and   >>   to switch to the previous or next date.



  1. After saving the changes you made on the table (2), click on the button       Replace False Zeros       to replace all the false zeros by missing values.

To replace all the values flagged as suspicious for all stations by missing values, use the following command to the R console:

indexFZ <- "/<path_to>/FALSE.ZEROS.CHECK_data/FalseZeros.rds"
CDT:::FalseZerosCheck_replaceAll(indexFZ, action = "all")

Change <path_to> with the exact path. The corrected data are located under the folder FALSE.ZEROS.CHECK_data/CDTSTATIONS.