Question
What does a large ‘Total error’ value represent in MIKE SHE water balance output and how do you fix it?
Answer
In MIKE SHE, the Total error represents the residual of the water balance equation:
Inputs − Outputs − Change in storage = Error
Time step is too large. This could result in processes with fast dynamics (overland flow, unsaturated flow, river coupling) becoming unstable and subsequently to not being able to resolve accurately, in which case the error could accumulate.
Fix: Reduce the computational time step or use adaptive time stepping where possible.Unstable unsaturated or saturated zone setup. This could be due to very thin layers or extreme hydraulic conductivities or sharp contrasts between soil layers.
Fix: Smooth parameter contrasts or review soil profiles and layer thicknesses.Misconfigured boundaries including river leakage boundaries, drainage levels above ground surface and groundwater head boundaries inconsistent with topography.
Fix: Recheck boundary elevations and sign conventions and verify river–groundwater exchange settings.Missing or incorrect storage terms.
If UZ/SZ/Snow storage components are disabled or inconsistent then water balance may numerically be inconsistent.
Fix: Ensure all relevant storage terms are enabled and compare change‑in‑storage against flux magnitudes.Coupling issues (MIKE SHE–MIKE+ Rivers). These could arise if river cross‑sections are too small or there are Courant issues in the river model or there is tight coupling with large groundwater gradients.
Fix: Refine river discretization or reduce river time step or check leakage coefficients.
A systematically increasing error indicates that there is probably something fundamentally wrongly defined in the model (in any of the model components or the boundaries), so that more water is gained/lost.
Sudden spikes are often linked to errors at the start‑up of the simulation or abrupt changes in the boundary conditions or activation of pumping, rivers, drains, or infrastructure.
In addition, the MIKE SHE Water Balance tool explicitly highlights the Error term as a key debugging output (as chart, time series, or spatial maps).
When looking at the water balance chart it may be worth double checking the ratios of evapotranspiration, surface runoff, groundwater recharge and irrigation as percentages of precipitation (do they fit with archived literature values). It may also be useful to assess the boundary conditions (are there any significant amounts leaving/entering the model from/to SZ and OL) and the UZ storage change (a relatively large value can be reduced by introducing a hotstart file in MIKE SHE ‘Simulation period’ dialog).
Please note, MIKE SHE prints a list of warnings (at the log files saved next to the model setup file but also at the results folder) that should point the user in the right direction for where to look in order to fix the water balance error.
How to debug efficiently
Consult the log files for any warnings related to mass errors.
Then use the Water Balance tool as intended, i.e.,
Check “Error of each component” time series and identify if error is dominated by overland, unsaturated, saturated or rivers flows.
Map the largest error term (accumulated / last time step). This should pinpoint where exactly in the domain the issue originates.
Shorten the analysis period and recalculate water balance for smaller time windows.
This should help isolate the triggering event.Compare against storage change. A large error relative to storage change usually corresponds to a numerical issue (i.e. not hydrological behavior).
Conclusion
It is recommended to look at the data inputs, the log files for warnings and the water balance outputs for the different water balance components. The Water Balance tool is designed also for debugging, not just reporting.
FURTHER INFORMATION & USEFUL LINKS
Manuals and User Guides
MIKE SHE Online Help: Total water balance
Training options
MIKE SHE – Getting started with integrated hydrological modelling