Well ... any method is in fact suitable ! What is the scale of your river basin ? and from which scale/variable do you want to downscale ? What is the time step ? (daily ?). I think you need to be more precise to get valuable answers.

Hi, two downscalling methods are recognized such as dynamical and statistical,  dynamic approach have a major computational cost and exist in some area but has a fine resolution in downscaling. In the statistical approach, you can use the three famous methods such as Lars-WG, SDSM and change factor (CF), After downscaling each method  base on your purpose time step,finally you can  develop the rainfall runoff models, for more information, please read the following article

Conference Paper Comparison of Statistical Downscaling Methods in Projecting ...

Hi Amir,

The suitability of a downscaling method depends on several factors. Besides the factors mentioned by Vincent also the purpose of the river basin study (e.g. modelling high flows, monhtly discharges or low flows) and the statistical properties of the related climatic variables play a role. How is the performance of the different methods in downscaling these relevant statistics of climatic variables from the GCM grid scale to the catchment scale or even small grid scale of a distributed hydrological model? Different methods will fit different purposes of downscaling.

This paper on "Representative general circulation models selection and downscaling of climate data" might be helpful:

https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/joc.6447