topic Build a model to calculate monthly average from daily rainfall rasters in ArcGIS Spatial Analyst Questions

Build a model to calculate monthly average from daily rainfall rasters

JessicaMoran1 — Wed, 23 May 2018 05:40:34 GMT

Hi All,

I have rainfall rasters for each day of the decade 2000 - 2009. Each file is named with the format rYYYYMMDD (eg r20001224 is the rainfall raster for Dec 24th 2000).

I would like to create 'monthly average rainfall' rasters for each month in this decade (10 years x 12 months = 120 rasters).

Rather than manually selecting each daily raster in a month, is there a way to get ArcGIS to select rasters with a common prefix as the input to Raster Calculator? i.e. generate a new raster by averaging all rasters named 'r200001__' (from January 2000).

Ideally, I would like to iterate this process in Model Builder using the Raster Calculator. I'm inexperienced with python coding, but I'm happy to learn if it's the only/best way.

Any advice is appreciated!

Re: Build a model to calculate monthly average from daily rainfall rasters

SteveLynch — Wed, 23 May 2018 11:36:10 GMT

Look at using ListRasters and feeding the result into CellStatistics

Re: Build a model to calculate monthly average from daily rainfall rasters

DanPatterson_Retired — Wed, 23 May 2018 12:09:57 GMT

This has been covered if you want to use scripting which may be easier

https://community.esri.com/message/766189-cell-statistics-with-list-rasters

Re: Build a model to calculate monthly average from daily rainfall rasters

XanderBakker — Sat, 11 Dec 2021 15:56:21 GMT

Scripting will probably be the easiest way to implement this using ListRasters—Help | ArcGIS Desktop and Cell Statistics—Help | ArcGIS Desktop as Steve Lynch already mentioned before.

To give you a head start with some of the code that will be needed, have a look at the snippet below:

lst_ras = ['r20000125', 'r20000126', 'r20000127', 'r20000128', 
           'r20000129', 'r20000130', 'r20000131', 'r20000201',
           'r20000202', 'r20000203', 'r20000204', 'r20000205']

lst_months = list(set([ras[:7] for ras in lst_ras]))
print(lst_months)

for month in lst_months:
    ras_names_month = [ras for ras in lst_ras if ras.startswith(month)]
    print("month: {}  rasters: {}".format(month, ras_names_month)) ‍‍‍‍‍‍‍‍‍‍

You will use ListRasters to get a list of raster names. In my example I created a small list manually (see lines 1 to 3). On line 5 I create a list of the month prefixes and print it on line 6. This will yield:

['r200002', 'r200001']‍

For each month prefix (line 😎 you can get a list of all the day rasters, which is done on line 9. This list is what you will use with the Cell Statistics as first parameter. The result of line 9 is printed on line 10 as yields:

month: r200002  rasters: ['r20000201', 'r20000202', 'r20000203', 'r20000204', 'r20000205']
month: r200001  rasters: ['r20000125', 'r20000126', 'r20000127', 'r20000128', 'r20000129', 'r20000130', 'r20000131']‍‍