WorldClim bioclim variables in Maxent: project and interpolate or use original coordinate system and resolution?

[Arne Loth]

I want to produce a Maxent model for an area in south Wales, UK. Almost all my environmental variables are in the OSGB coordinate system and have a 25m resolution. I also want to include bioclimatic conditions and have identified the WorldClim dataset as the best source of open data for this.

The 19 bioclimatic variables available through WorldClim all come as TIFF files in WGS1984 at a resolution of 30 seconds, or about 1km. Will I need to convert these files to OSGB or can they stay in WGS1984? In other words, does Maxent work when not all of the variables are in the same projection?

In terms of resolution, does it make sense to try to interpolate the data from 1km to 25m? I have attempted this by:

- Clipping the raw data to my study area

- Using 'Project raster' to convert from WGS1984 to OSGB

- Converting the resulting raster to points

- Running the 'Spline' tool on the new point shapefile, specifying 25m as the new cell size. 

The tool succeeded but gave me multiple warnings saying that 'collinear points have been dropped'. Should I ignore this warning or does it mean something has gone wrong? Is it generally a good idea to try and 'improve' the resolution of bioclim data in this way? 

This is my first ever attempt at Maxent, and at dealing with datasets in different projections, so any advice, no matter how basic, would be greatly appreciated. 

[Francisco Rodriguez Sanchez]

Hi Arne,

Yes, all variables (and occurrence data) must have the same projection.

If you are dealing with a small area in UK (i.e. not global, or continental), I would recommend looking for a high-resolution climate dataset (i.e. probably focused on UK only) other than Worldclim. The 1-km resolution layers in Worldclim are already highly interpolated. I wouldn't trust further interpolations going down to 25 m.

Sorry I'm not familiar with UK climate datasets, but I'm sure there must be something of higher resolution.

Hope this helps, and good luck with your first Maxent job!

Paco

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