how to down scale climatic data?

[desalegn chala]

Hello guys,

I am working on maxent model. I am using SRTM DEM derived topographic varaiables along with climatic and other data. The DEM and the cliamtic variables have different resolutions. Any one who has the idea on how to down sclae the climatic variables that are obtained from the worldcliam to a resolution of 90 m in ARC_GIS enviroment. I have tried resampling but it gives unreliable ranges of vaues

 

regards

 

Desalegn
 

 

 

[David Galbraith]

probably with the 'resample' tool in ArcMap.  You'll need to insure that the snap raster and analysis extent are set correctly for each grid or Maxent will choke on the grids because they'll have different numbers of rows and columns.

Dave

--
You received this message because you are subscribed to the Google Groups "Maxent" group.
To post to this group, send email to max...@googlegroups.com.
To unsubscribe from this group, send email to maxent+un...@googlegroups.com.
For more options, visit this group at http://groups.google.com/group/maxent?hl=en.

[Jesús Muñoz]

downscaling is not a trivial process. It is not simply to resample, which is easily done in ArcMAP (values shouldn't be unrealistic, you did something wrong). Downscaling takes other variables (vegetation, elevation, etc.) to "adapt" the original dataset to smaller scales.

 

I would recommend you not to try anything as you are trying now, but derivate variables from the 90 m SRTM dataset that fit your needs (concavity can be a surrogate for water accumulation; if the area is "cloud-free", you can generate a radiation layer or energy input, which would be a surrogate for temperature... and so on)

 

Jesús

 

 

 

*************************************************************************

Jesús Muñoz                  e-mail: jmu...@rjb.csic.es

Real Jardín Botánico (CSIC)

Plaza de Murillo 2           tlf. +34 91 420 3017

E-28014 Madrid               fax. +34 91 420 0157

ESPAÑA (Spain)

 

http://www.masterenbiodiversidad.org

 

http://www.rjb.csic.es/jardinbotanico/jardin/contenido.php?Pag=413&tipo=cientifico&cod=66

 

KRAKEN research group (environmental modelling, data processing & analysis):

                            http://www.unex.es/investigacion/grupos/kraken

 

SYNTHESYS: EU funds short visits to our institution:

http://www.synthesys.info/index.htm

*************************************************************************

 

__________ Información de ESET Smart Security, versión de la base de firmas de virus 6202 (20110613) __________

 

ESET Smart Security ha comprobado este mensaje.

 

http://www.eset.com

__________ Información de ESET Smart Security, versión de la base de firmas de virus 6202 (20110613) __________

ESET Smart Security ha comprobado este mensaje.

http://www.eset.com

[David Galbraith]

Desalegn,

Jesus is right that downscaling is non-trivial.  The bioclim variables were developed at specific scales based on the source data available from remotely sensed sources.  Since the resolution of topographic data is one of these inputs, resampling to a finer resolution will not produce realistic values at a finer scale (at some large scale, the topographic complexity of entire mountain ranges can be oversimplified).  If ambient air temperature is what is biologically important, it may vary considerably from solar radiation based on aspect and slope, but only if it is possible to accurately depict local aspect and slope from DEMs.  If contributing watershed area is important, then local concavity won't reflect the network organization of the larger watershed, but may be the best thing available if a reliable network of streams, rivers, and catchments is unavailable.

I've run in to 'weird' numbers from resampling while using cubic convolution or bilinear interpolation on continuous raster data, both of those algorithms have the potential to produce surfaces with data ranges outside the bounds of input data based on data trends observed from the set of cells used to produce the output grid.  The nearest neighbor algorithm can also produce some weirdness when used on continuous grids, because it basically uses the cell center to define which underlying cell's value is used when resampling from a finer to a coarser scale.  Going from coarser to finer scales, it will produce blocks of cells that all have the same values rather than a nice smooth surface.

Dave

[metodos normalizadso de analisis de agua]

Hi,

i´m working with arcmap, and im using a 90m dem and the worldclim
temperatura data oh ~100 Ha. im using extract by mask and in the
environments and raster analysis Settings and i choose, in cell size,
minimum of inputs, and the result is the 1Ha pixels. i want to konw if
that is a validate metodology???

> > Plaza de Murillo 2           tlf.+34 91 420 3017begin_of_the_skype_highlighting            +34 91 420 3017      end_of_the_skype_highlighting

>
> > E-28014 Madrid               fax. +34 91 420 0157
>
> > ESPAÑA (Spain)
>
> >http://www.masterenbiodiversidad.org
>

> >http://www.rjb.csic.es/jardinbotanico/jardin/contenido.php?Pag=413&ti...

>
> > KRAKEN research group (environmental modelling, data processing &
> > analysis):
>
> >                            http://www.unex.es/investigacion/grupos/kraken
>
> > SYNTHESYS: EU funds short visits to our institution:
>
> >http://www.synthesys.info/index.htm
>
> > *************************************************************************
>

> > *De:* max...@googlegroups.com [mailto:max...@googlegroups.com] *En nombre
> > de *David Galbraith
> > *Enviado el:* Monday, June 13, 2011 9:02 AM
> > *Para:* max...@googlegroups.com
> > *Asunto:* Re: how to down scale climatic data?

>
> > probably with the 'resample' tool in ArcMap.  You'll need to insure that
> > the snap raster and analysis extent are set correctly for each grid or
> > Maxent will choke on the grids because they'll have different numbers of
> > rows and columns.
>
> > Dave
>

> > On Mon, Jun 13, 2011 at 9:31 AM, desalegn chala <dchala...@yahoo.com>