*When I refer to climatology here I am referring to a thirty year timeslice which is averaged monthly to produce a climatology (year of average data) for a specific variable.

I have a high resolution 'baseline' climatology grid which is of size 4320 x 8640 x 12 (lat x lon x time(months)) (baseline.Tmax below). This is stored in a list in a netcdf file.

I also have produced a lower resolution 'change surface' for a future climate scenario by subtracting the modelled baseline climatology (Tmax.h) from the future climatology (Tmax.f). This results in a climatology grid of size 180 x 288 x 12 (lat x lon x time) (Delta.Tmax below).

#baseline.Tmax = Climatology of observed Tmax from 1980-2009
#Tmax.h        = Climatology of modelled Tmax from 1980-2009
#Tmax.f        = Climatology of modelled Tmax from 2065-2095
#create the change surface
Delta.Tmax <- gridArithmetics(Tmax.f, Tmax.h, operator = "-")
#Then add it to the baseline
Tmax_modelled <- gridArithmetics(baseline.Tmax, Delta.Tmax, operator = "+")

What I want to do is add this change surface to the baseline climatology to get a future climate change scenario for this variable (Tmax_modelled above), but in a very specific way:

I have already tried 'coarsening' the baseline to match the resolution of the change surface, which results in a simple grid arithmetic to add the two together (which is what I did above. The coarsening was carried out using a cdo regrid command).

However, what I really want to do is to add the change surface to the baseline WITHOUT altering the baseline resolution. I think in order to do this, I would need a fishnet of identical size to the baseline, which would then be overlaid on the change surface and the values in the change surface would be taken on by the new fishnet. So, where there was only one grid cell of value 1.2 in the change surface, there may be (for example) 100 grid cells from the fishnet occupying that one grid cell, which would all assume the value 1.2. Hopefully my explanation makes sense. I see that this is possible in ArcGIS from some of the posts here (below) but I really want to automate the process in R. I think that this post is useful: Generate rectangular fishnet or vector (grid cells) shapefile in R? I think I need to create a fishnet (as in the post above) in R and somehow overlay it on my baseline.

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