Please change the Initial Time Step and Minimum Time Step. Also, increase the number of Iteration Criteria like 100, 10000 etc. Then, it will be solved.

Thank you, Md. Abdul Kader . I will try and see.

Refer to https://www.pc-progress.com/Documents/Notes_on_Spatial_and_Temporal_Discretization.pdf. It could be due to the wrong model setting, time discretization, or spatial discretization. Changing iteration criteria will not help.

Agree with the above answer. Changing the time step and iteration criteria cannot solve the problem at the source. The calculation principles of HYDRUS should be known.

Thank you Sahila Beegum and Wei Mao . After changing time steps and iteration time, simulation is taking huge time to run (more than one hour for simulating 16 days only, my simulation for 1 year and that's why I skipped that).

So, still struggling with the same problem. I can see if I reduce irrigation amount or rainfall from its higher value then it works. But I can't understand why it can't taking a larger value if my irrigation amount is larger? Any further suggestions on that?

Sahila Beegum Your link does work. Could you please send it again?

I am getting this type of problems all the time. Referring to the Hydrus1D manual (https://www.pc-progress.com/Downloads/Pgm_hydrus1D/HYDRUS1D-4.17.pdf). In some of the cases the problem did not occurred, when I increased the grid resolution at the top of the soil profile while leaving it relatively coarse at the base of it.

Convergency problem not easy to solve, just following the suggestion above, try to adjust the time and space discretization, and finally initial condition if nothing left to adjust.

Refer to the attached file

Thanks to all. I am trying to fix it by changing soil type, initial and minimum time steps, number of nodes and grid resolution. Let's see what happen there.

Hi @Rahena Parvin Rannu, Did you manage to solve the convergence issue? My understanding is that changing soil type may not be a wise decision as it is unrealistic to change the real system for the simulation. Instead, please check and play with the model parameters, initial and boundary conditions, and most importantly the target accuracy level that was set for your simulation. As you mentioned earlier, higher values of some variables were causing problems. Sometimes inconsistency among the variables prevents the simulation from reaching to the convergence with the specified accuracy level. As far as I understand, number of nodes and grid resolution have nothing to do with the convergence; both are related to computational time requirements and accuracy of your simulation results.

Dilip Kumar Roy dada thank you. I tried to improve the accuracy of my input variables but still stuck with the same problem if I use hydraulic conductivity 0.48 cm/day for silty clay soil. But if I change this HC value then I don't get my expected output. Do you have any further and specific suggestions?

I agree with the opinion of Dilip Kumar Roy

Thanks to all. I got it.