Hello Ahmadi Mehamoui ,

Did you use the same CN for for all land use change scenarios. for example.

LU Scenario 1: for forest you used CN=75

LU Scenario 2: for forest you used CN=75 etc.?

How are you implementing your scenarios?

I am not familiar with SWAT. But, I think, the parameters for ET and other modules should fixed after calibration and validation. Then, LC （land use change) scenarios actually represent area change of land use types. ET and runoff should be change when using another LU scenario.

I had a similar experience. In my case, Q does not change much but I observed that there is a change in the contribution of different runoff components (surface runoff, lateral flow, baseflow) to total streamflow. For ET, might be the spatial pattern should be different after changing land use

hello, Ahmedi

You should only concentrate only on this area where changes in land use are more and increase more.

If you take the whole catchment then the impact of runoff due to land-use change is very less. so My suggestion is this you should only concentrate on the region which changes rapidly.

I encountered the same issue. To solve the issue, you should double check your parameters and make sure that you used correct parameters. make sure you change parameters when you move from baseline to scenario. after you should compare ET and runoff data from output file. ET and Runoff should change.

You are probably using SWAT with SCS-CN runoff generation mechanism. You need to remember that the land use change by itself will not necessarily change the runoff if the parameters assigned to that land use within SWAT database are somewhat similar or close to each other. Now, if you are changing the land use from agriculture or forest to urban, your runoff component values should definitely change. But there is a good chance that the results will not change much when the land use changes from some agriculture crop to another with similar characteristics. If the land use change is significant (e.g. ag to urban) and you still do not see any change in runoff components, there might be some issues in the approach for assigning the land use categories between the scenarios. Check the output.hru for each scenario to see if the land use categories are changed appropriately and if not, redo the HRU definition with correct land use assignment. Hope this helps.

Define appropriate new land use parameters to see the change. Also double-check the HRU definition step to see whether the new land use were properly classified or not.

Dear Ahmadi Mehamoui,

land use change impacts often balance out if aggregated over space and time. I would therefore recommend to look at changes at the sub-basin or HRU-level as well as to look at dynamic changes. In this respect, the following three papers might help you:

Article An assessment of land use change impacts on the water resour...

Article Dynamic integration of land use changes in a hydrologic asse...

Article Comparing the effects of dynamic versus static representatio...

However, if your output at smaller spatial scales is still exactly the same, it is very likely that the change was not correctly implemented. In this case, check your inputs and the model and try again.

Good luck and kind regards,

Paul

Ahmadi Mehamoui could you please specify which years land use you are using for SWAT Model simulations? Because, LU change is a slow processess, if you are looking for one or two years then it might be no change in the hydrology of the area. However, larger time duration shows its impacts.... Furthermore, could you explain how you are validating the Calibrated SWAT Model for one land use.

Naveed