I have 12 years of stream flow data and 40 years data is downscaled. I have seen lot of papers but actual procedure is never mentioned? Please do answer if anybody knows.
Could you be more precise? What is this 40 year downscaled data? Do you mean that additionally to your 12 years flow you also have rainfall data derived by downscalling of weather models ?
Yeah!!!... 40 years data is used for model building (calibration and validation in SDSM) and next to hydrological modelling in SwAT how to use this output?? @Rafael Anleu
If you are looking for a general manual for SWAT, see this link:
http://swat.tamu.edu/documentation/
Unfortunately the information you are providig is still confusing. Could you give the periods (dates) for which you have runoff data, true measured rainfall data and modelled rainfall data. Otherwise the answer is going to be more confusing.
rainfall data for the period 1973 to 2013 and runoff data for 2000 to 2013.
OK.I will try to give you a practical answer to your question, but before that a word of caution.
The first step is to calibrate your modell (you call this model building, but this step is usually called model calibration). To do this, you need rainfall and runoff data for the same period. The issue here is that IF YOU only have "modelled" rainfall and depending on what type of modelling technik was used to produce this rainfall, you can at best hope for:
- the model to reproduce the statistical characteristics of rainfall (number of rainfall days, totals, event extremes, std. dev. and so on if you are deriving rainfall from a so called "weather generator" which is not the same as a large scale or regional scale weather model.
- or for the model to mirror rainfall ocurrence without actually managing to reproduce many of the statistical characteristics (extreme events most notably) if you are deriving rainfall from downscaling a large scale or regional scale weather model. No weather model is really able to reproduce rainfall events accurately on a daily basis in a way that they will match the actual ocurred rainfall in terms of spatial and time distribution and magnitude and from then on that it will match the runoff response.
But the thing is, that in order to derive rainfall from any of this two model types in a "proper" way you need actual ground measurements. So maybe you should check into this. With that being said, here comes the practical part.
First: Divide your period 2000 - 2013, for which you have both rainfall and runoff data, in two parts. Lets say 2000 - 2008 and 2009 - 2013, wich I will cal Set A and Set B.
Second: calibrate your model with rainfall data from Set A. How to use this in SWAT? As far as I know SWAT can only use point data in a table format; that is data from weather stations. If your modelled rainfall is already like this, then great, you only have to place it in the correct format for SWAT to read it. If on the other hand, you have rasterized data, then some extra work is needed. You need to define "dummy weather stations" and extract your rainfall data for this locations from your rasterized data (yes, if you have one rasters for each day it could be tedious, so you may look into some way of automatizing the extraction process). Here you also have to decide on the ammount and location of "dummy stations" to minimize information loss (If it happens that you do have some ground observations I would define my dummy stations so that they match the location of the ground stations and maybe a few extra "dummy stations" to increase spatial resolution).
Third: use Set B to validate the model. That is without adjusting model parameters see how well you can reproduce observed runoff.
Fourth: use your validated model to make some prediction or in your case you may reconstruct runoff for the period 1973 - 2000. Hope it helps a little more. What are your objectives? What are you trying to do?
Thank you so much for your detailed answer, it helps me for sure.
Actually I am downscaling rainfall of the study area for climate change impact assessment and its effect on water availability (SWAT-GIS interface), also the effect of climate change on land use land cover of the study area.
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