preprocess the precipitation (Netcdf data) for further analysis

Hi all,

I am really new at MatLab so please forgive my ignorance.

Here is my issue- I have downloaded cmip6 data for precipitation from ACCESS-CM2 model. There are 18 nc file altogether. I need to perform following actions. The variables are lat, lon, pr and time.

1. Open all the nc files together
2. The time is stored as numerical serial number, so it has to change in the date format, the reference date is 1850-01-01.
3. Extract the values of precipitation for 1990 to 2100
4. And Regrid the data

I can do these steps individually, but if I want to do the steps all in one it is not working.

I am really stuck. If someone can help me that would be really great.

Thanks in Advance.

Answer 1

[Udit06]

Hi Fatimatuj,

I understand that you are looking for a way to process multiple NetCDF files to handle CMIP6 precipitation data from the ACCESS-CM2 model in MATLAB and are able to preprocess each NetCDF file individually. You can use a for loop as shown in the code snippet given below to preprocess each .nc file one by one.

% Reference date for converting serial time numbers
referenceDate = datetime(1850, 1, 1);

% Time range for extracting precipitation data
startDate = datetime(1990, 1, 1);
endDate = datetime(2100, 12, 31);

% Loop over each NetCDF file
for i = 1:length(ncFiles)
    % ncFiles contains full path of each .nc file
    ncFile = ncFiles(i);
    
    % Read latitude, longitude, precipitation (pr), and time variables
    lat = ncread(ncFile, 'lat');
    lon = ncread(ncFile, 'lon');
    pr = ncread(ncFile, 'pr');
    time = ncread(ncFile, 'time');
    
    % Convert time to datetime format
    time = referenceDate + days(time); % Adjust this if your time units are not in days
    
    % Find indices of time within the desired range (1990 to 2100)
    timeIndices = find(time >= startDate & time <= endDate);
    
    % Extract precipitation data for the desired time range
    pr = pr(:, :, timeIndices);
    
    %regrid the data as per your requirement
end

You can refer to the following MathWorks documentations to understand more about "datetime" and "ncread" functions in detail respectively.

• https://www.mathworks.com/help/matlab/ref/datetime.html
• https://www.mathworks.com/help/matlab/ref/ncread.html

I hope this helps.

[Fatimatuj Zohara Sonny]

Thank you so much for yor reply. I really appreciate his.