How do I convert ERA Interim precipitation to get total precipitation in area?

i download time series data from

ERA5 monthly averaged data on single levels from 1959 to present

for every month I have a NC file

"units = 'm of water equivalent'

As wrote in this link:

https://confluence.ecmwf.int/pages/viewpage.action?pageId=197702790

I must multiply every month in number of its days to get total precipitation (m) in every month

my question is because the data is 41*41*64 do i average data or sum of data in every month of a year?

who I can calculate the total precipitation in a year?

filename1='ep1.nc';% data jan

p1=ncread(filename1,'tp');

[llats1,llons1] = meshgrid(lats1,lons1);

land1 = island(llats1,llons1);

p1(land1)=NaN;

Is it for every month:

pmm1(:,1)= nanmean(nanmean(p1))*31;

or

pmm1(:,1)= nansum(nansum(p1))*31;

Answer 1

[Sulaymon Eshkabilov]

Here is how to compute annual and weekly averages of the data given in nc file.

unzip('ep1.zip')
vardata=ncread('ep1.nc', 'tp');
% This computes annual average
for ii=1:64
Year_mean(ii) = mean(vardata(:,:,ii), 1:2);
end
plot(Year_mean, 'ro-.', 'MarkerFaceColor','c'), shg
title('Annual average')
xticks([1:5:64 64])
Year = {'1959', '1964', '1969', '1974', '1979', '1984', '1989', '1994','1999', '2004', '2009', '2014', '2019', '2023'};
xticklabels(Year)
grid on
xlabel('Years')
ylabel('Precipitation, [m]')
xlim([1, 64])

%%
vardata=ncread('ep1.nc', 'tp');
% This computes weekly average
for ii=1:64
    for jj=1:41
      Week_mean{ii, jj} = mean(vardata(:,:,ii), 1);
    end
end

[Mahboubeh Molavi-Arabshahi]

Dear Sulaymon Eshkabilov

thanks for your reply

please let me explain what i need, i want to calculate total precipitation in every year so i download every month separately (41*41*64) for 64 years.

so because i need just data Sea so i used island

(because of internet i could not attach all of 12 months's data)

My doubt at first is: do i need mean or sum of value to calculate total precipitation in whole of sea?

I comment it on matlab file that is attached because i tried it with both cases

and another question is do i need to multiply the values of precipitation every months at first in a scale factor because the value of so small and they are not same as observed data.

in netcdf file they told the units are "m of equivalent water" i need data total precipitation in every year based on Km

thanks for your help