How does SWAT assign weather data to each sub-basin?

[S K]

Hi,

I am using SWAT and have prepared WGEN_USER file. I want to know how SWAT uses climate data from given weather stations.
(1) As I understand (maybe wrong), SWAT uses WGEN_USER data (nearest station statistics) to fill missing values of given stations. How does SWAT assign weather data for each sub-basin? Does it take the same weather data from the given station nearest to the centroid of each Sub-basin? OR does it estimate weather data for each sub-basin (considering a new weather station at the centroid of sub-basin) using any other approaches?
(2) Although I have many (around 80) rainfall and temperature stations in my study catchment (50000 Km2), I have only 5 stations for solar radiation, wind speed, and relative humidity. How does SWAT assign these values for each sub-basin based on 5 station data? Does it take same weather values from one of these 5 stations based on proximity to its centroid?
Thank you in advance.

Regards,
Santosh

[Janardan Joshi]

Dear Santosh,

Yes swat adopts the nearest station to its centroid for all weather data and uses the WGEN_USER file to replace the missing data (and nothing otherwise as far as i know).

The solution for including data of multiple stations is that first of all you use thiessen polygon and average the weather data over a subbasin. While preparing the 

pcp,tmp and other input files you specify the coordinates of the stations (obtained after averaging) as the centroid of each basin as you will have the same number 

of pcp files as the number of subbasins.

Hope it helped you.

Best

Janardan

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[Natalja C.]

Hello,
To add to the previous comment, if you do the setup with arc/qswat, the "stations" are split into rainfall, solar, tmp, hmd, wnd. So a single subbasin may be assigned to pcp station 1, solar station 5, tmp station 3, etc., if they are situated in different points.
So in your case, the pcp (and other observations) will be from these 80 stations, but slr only from 5.
Hope I explained it understandably :)
Best,
Natalja

[majid...@gmail.com]

Hi Natalja,

When entering weather data, when choosing WGEN_user it shows station count: 4. Does this mean SWAT is only using 4 stations for writing weather data? because I have more than 4 pcp and wind stations and 2 tmp and hmd stations. Or are these 4 stations the ones used to fill in missing data?

Regards,

Majid

[Natalja C.]

Hello,

I'm not sure what it means, as I have worked with ArcSWAT a long time ago.

To help you identify the answer yourself, here is some information:

- the number of used solar, wind, tmp, pcp and hmd stations is located in the file.cio file  (NRTOT, NTOT, NSTOT, NHTOT, NWTOT). 

- ArcSWAT will assign the closest station to subbasin centroid, meaning that if there are multiple station in one subbasin, only one gets assigned. This means that despite having multiple stations, you will end-up with one per subbasin, which may be re-used.

               i.e. Station 1 - subbasins 1, 2, 6; station 2 - subbasins 3, 4, 5. Station 3 - not assigned, because it was too far.

Best,

Natalja