Abstract. Numerical modeling provides an opportunity to quantify
the reaction of lakes to alterations in their environment, such as changes
in climate or hydrological conditions. The one-dimensional hydrodynamic
General Lake Model (GLM) is an open-source software and widely used within
the limnological research community. Nevertheless, no interface to
process the input data and run the model and no tools for an automatic
parameter calibration yet exist. Hence, we developed glmGUI, a graphical user
interface (GUI) including a toolbox for an autocalibration, parameter
sensitivity analysis, and several plot options. The tool is provided as a
package for the freely available scientific code language R. The model
parameters can be analyzed and calibrated for the simulation output
variables water temperature and lake level. The glmGUI package is tested for two sites (lake Ammersee, Germany, and lake
Baratz, Italy), distinguishing size, mixing regime, hydrology of the
catchment area (i.e., the number of inflows and their runoff seasonality),
and climatic conditions. A robust simulation of water temperature for both
lakes (Ammersee: RMSE =1.17 ∘C; Baratz: RMSE
=1.30 ∘C) is achieved by a quick automatic calibration. The
quality of a water temperature simulation can be assessed immediately by
means of a difference plot provided by glmGUI, which displays the distribution of
the spatial (vertical) and temporal deviations. The calibration of the lake-level simulations of lake Ammersee for multiple hydrological inputs
including also unknown inflows yielded a satisfactory model fit (RMSE =0.20 m). This shows that GLM can also be used to estimate the water balance
of lakes correctly. The tools provided by glmGUI enable a less time-consuming and
simplified parameter optimization within the calibration process. Due to
this, i.e., the free availability and the implementation in a GUI, the presented R
package expands the application of GLM to a broader field of lake modeling
research and even beyond limnological experts.