Dear Ahmad,

If you search the Web for "weather generator", you'll find over 500,000 links. For general information and an introduction to the topic, see

http://www.ipcc-data.org/guidelines/pages/weather_generators.html

http://unfccc.int/adaptation/nairobi_work_programme/knowledge_resources_and_publications/items/5510.php

Both of these sites include references to published works on this topic. The following papers may also provide guidance or further suggestions:

http://www.sciencedirect.com/science/article/pii/S136481520700031X

http://www.mssanz.org.au/modsim09/I13/hashmi.pdf

I hope this helps. Cheers, Michel.

Dear Ahmad,

you may want to check the weather generator chapter and the references in our review paper (on my researchgate page), Maraun et al., Precipitation Downscaling under Climate Change: Recent developments to bridge the gap between dynamical models and the end user, Rev. Geophys., 2010.

I can definitely recommend the glimclim package by Richard Chandler (University College London), but it requires probably more statistical knowledge than the methods listed in the answer above.

Best wishes,Add your answer

Douglas

I suggest you use the global reanalysis data such as NCEP/DOE Reanalysis II data, for large spatial scale and temperal scale it can obtain relative stable results. The link is http://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis2.html

And for east Asia and Middel East Asia, another data for rainfall which name is APHRODITE, is also a good choice, the link is http://www.chikyu.ac.jp/precip/, however for this data the end data is 2007/12/31

I hope my tips can help you 

Thanks dear Yang Yan;

Your suggestions are acceptable, but in the second step of my project. At the first step I want to test the applicability of such datasets you mentioned above, so I need some observed data to test the goodness of them, but as I said in the question, the coverage of observed data for Afghanistan is weak and the scale of precipitation in monthly in most stations. so I have to downscale the monthly ones to daily.

Hi

You can run KNN weather generator for any time rather than similarity of historical data KNN-WG there is in http://www.AgriMetSoft.com