Evaporation is not being deducted from the water column

Question

Hi Chris,

I’m working on a model using the May 2026 development version. I noticed that evaporation does not appear to be removing water mass from the lake, even though ievap_vol is set to 1. (I ran some tests setting it to zero and 2 and the results were almost identical)

When I output evaporation, it appears to be calculated correctly, and the values make sense in terms of the annual water balance. However, it does not seem to be applied to the water column or reflected in the lake volume.

Could this be a numerical issue, perhaps related to the grid resolution? My horizontal grid is 30 × 30 m, with 0.5 m vertical layers. Is there a way to confirm whether evaporation is being accounted for in the water balance?

Thanks,
Ali

Answer 1

Hi Ali,

ievap_vol should be 1 or 0.

If 0 the thermodynamics of evaporation are calculated but the volume is not removed.

This is generally used if there are inflows/outflows that have been calculated using a water balance based off measured water levels that has not taken into account evaporation.

One thing to check is your volume.csv txtfile to see if your  Expected inflow/outflow Volume in timestep and Inflow volume in timestep match up.

If they don't this is usually due to disconnected cells in the bathymetry near where inflows come in which can cause issues with the free surface solution. You can find these cells by looking at a sheet movie the cells will flash between being wet and dry and you'll need to smooth your bathymetry to ensure diagonal cells are connected.

Chris